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THE

POETRY OF SCIENCE;

OR,

STUDIES

OF THE

PHYSICAL PHENOMENA OF NATURE.

BY

ROBERT HUNT,

AUTHOR OF

“RESEARCHES ON LIGHT;” “ELEMENTARY PHYSICS;”
“PANTHEA, OR THE SPIRIT OF NATURE,” ETC.

PROFESSOR OF PHYSICS, METROPOLITAN SCHOOL OF SCIENCE, ETC., ETC.

THIRD EDITION, REVISED AND ENLARGED.

LONDON:

HENRY G. BOHN, YORK STREET, COVENT GARDEN.

MDCCCLIV.


  From Shakespeare to Plato--from the philosophic poet to the poetic
      philosopher--the transition is easy, and the road is crowded with
      illustrations of our present subject.

       *       *       *       *       *

  Hast thou ever raised thy mind to the consideration of EXISTENCE, in
      and by itself, as the mere act of existing?

  Hast thou ever said to thyself, thoughtfully, IT IS!--heedless, in
      that moment, whether it were a man before thee, or a flower, or
      a grain of sand,--without reference, in short, to this or that
      particular mode or form of existence? If thou hast, indeed,
      attained to this, thou wilt have felt the presence of a mystery,
      which must have fixed thy spirit in awe and wonder.

                                        _Coleridge._

               LONDON:
          WILSON and OGILVY,
          57, Skinner Street.




PREFACE.


Since 1848, when the “Poetry of Science” was first submitted to the
public, two editions have been exhausted. This, were proofs required,
would of itself show that there is a large circle of readers to whom
the deductions of science have an unfailing interest. Beyond this,
it conveys an assurance that every truth, however abstract it may
appear, has a large popular value if studied in its relations to
those generalities which embrace great natural phenomena. With this
persuasion the third edition of the “Poetry of Science” has been
extended so as to include all the important discoveries which have
been made in Natural Philosophy to the end of the year 1853. It is now
presented to the world in a new and cheaper form, in the hope, that,
with the extension of its circulation, there may be awakened, in still
larger circles, a deep and healthful interest in the sciences of which
the volume treats.

                                        R. H.

Edinburgh, March 7, 1854.




CONTENTS.

                                                              Page


  PREFACE.                                                     iii

  CONTENTS.                                                      v

  INTRODUCTION.                                                 ix


  CHAPTER I.

  GENERAL CONDITIONS OF MATTER.

  Its varied Characters, and constant change of
  external Form--The Grain of Dust, its Properties and
  Powers--Combinations in inorganic Masses and in organized
  Creations--Our knowledge of Matter--Theory of Ultimate
  Atoms--The Physical Forces acting on the Composition
  of Masses--The certainty of the exercise of subtile
  principles, which are beyond the reach of experimental
  Science                                                        1


  CHAPTER II.

  MOTION.

  Are the Physical Forces modes of Motion?--Motion
  defined--Philosophical Views of Motion, and the Principles
  to which it has been referred--Motions of the Earth and
  of the Solar System--Visible Proofs of the Earth’s Motion
  on its Axis--Influence of the proper Motions of the Earth
  on the Conditions of Matter--Theory of the Conversion of
  Motion into Heat, &c.--The Physical Forces regarded as
  principles independent of Motion, although the Cause and
  often apparently the Effects of it                             7


  CHAPTER III.

  GRAVITATION.

  The Forms of Matter--Shape of the Earth--Probability
  of the Mass forming this Planet having existed in a
  Nebulous State--Zodiacal Lights--Comets--Volatilization
  of Solid Matter by Artificial means--The principle
  of Gravitation--Its Influence through Space and
  within the smallest Limits--Gravitating powers of the
  Planets--Density of the Earth--Certainty of Newton’s Law
  of the Inverse Square--Discovery of Neptune--State of a
  Body relieved from Gravitation--Experiment explaining
  Saturn’s Ring, &c.--General inference                         21


  CHAPTER IV.

  MOLECULAR FORCES.

  Conditions of Matter--Variety of organized
  Forms--Inorganic Forms--All matter reducible to the
  most simple conditions--Transmutation, a natural
  operation--Chemical Elementary Principles--Divisibility
  of Matter--Atom--Molecules--Particles--Molecular
  Force includes several Agencies--Instanced
  in the Action of Heat on Bodies--All Bodies
  porous--Solution--Mixture--Combination--Centres
  of Force--Different States of Matter (Allotropic
  Conditions)--Theories of Franklin, Æpinus, and
  Coulomb--Electrical and Magnetic Agencies--Ancient
  Notions--Cohesive Attraction, &c.                             35


  CHAPTER V.

  CRYSTALLOGENIC FORCES.

  Crystallisation and Molecular Force
  distinguished--Experimental Proof--Polarity of
  Particles forming a Crystal--Difference between
  Organic and Inorganic Forms--Decomposition of
  Crystals in Nature--Substitution of Particles in
  Crystals--Pseudomorphism--Crystalline Form not dependent
  on Chemical Nature--Isomorphism--Dimorphism--Theories of
  Crystallogenic Attraction--Influence of Electricity and
  Magnetism--Phenomena during Crystallisation--Can a change
  of Form take place in Primitive Atoms?--Illustrative
  Example of Crystallisation                                    50


  CHAPTER VI.

  HEAT--SOLAR AND TERRESTRIAL.

  Solar and Terrestrial Heat--Position of the Earth
  in the Solar System--Heat and Light associated in
  the Sunbeam--Transparency of Bodies to Heat--Heating
  Powers of the  Rays of the Spectrum--Undulatory
  Theory--Conducting Property of the Earth’s
  Crust--Convection--Radiation--Action of the Atmosphere on
  Heat Rays--Peculiar Heat Rays--Absorption and Radiation
  of Heat by dissimilar Bodies--Changes in the Constitution
  of Solar Beam--Differences between Transmitted and
  Reflected Solar Heat--Phenomena of Dew--Action of
  Solar Heat of the Ocean--Circulation of Heat by the
  Atmosphere and the Ocean--Heat of the Earth--Mean
  Temperature--Central Heat--Constant Radiation of Heat Rays
  from all Bodies--Thermography--Action of Heat on Molecular
  Arrangements--Sources of Terrestrial Heat--Latent Heat
  of Bodies--Animal Heat--Eremacausis--Spheroidal State
  Cold--Condensation--Freezing--Theories of Heat--Natural
  Phenomena--and Philosophical Conclusion                       62


  CHAPTER VII.

  LIGHT.

  Theories of the Nature of Light--Hypotheses
  of Newton and Huygens--Sources of Light--The
  Sun--Velocity of Light--Transparency--Dark
  Lines of the Spectrum--Absorption of
  Light--Colour--Prismatic Analysis--Rays of the
  Spectrum--Rainbow--Diffraction--Interference--Goethe’s
  Theory--Polarisation--Magnetisation of Light--Vision--The
  Eye--Analogy--Sound and Light--Influence of Light on
  Animals and Vegetables--Phosphorescence arising from
  several Causes--Artificial Light--Its Colour dependent on
  Matter                                                       118


  CHAPTER VIII.

  ACTINISM--CHEMICAL RADIATIONS.

  The Sun-ray and its Powers--Darkening of
  Horn Silver--Niepce’s Discovery--Prismatic
  Spectrum--Refrangibility of Light, Heat, and
  Actinism--Daguerre’s Discovery--Photography--Chemical
  Effects produced by Solar Radiations--Absorption of
  Actinism--Phenomena of the Daguerreotype--Chemical
  Change produced upon all Bodies--Power of Matter to
  restore its Condition--Light protects from Chemical
  Change--Photographs taken in Darkness--Chemical Effects
  of Light on organized Forms--Chemical Effects of Solar
  Heat--Influence of Actinism on Electricity--Radiations in
  Darkness--Moser’s Discoveries, &c.                           166


  CHAPTER IX.

  ELECTRICITY.

  Discovery of Electrical Force--Diffused through all
  Matter--What is Electricity?--Theories--Frictional
  Electricity--Conducting Power of Bodies--Hypothesis
  of two Fluids--Electrical Images--Galvanic
  Electricity--Effects on Animals--Chemistry of Galvanic
  Battery--Electricity of a Drop of Water--Electro-chemical
  Action--Electrical Currents--Thermo-Electricity--Animal
  Electricity--Gymnotus--Torpedo--Atmospheric
  Electricity--Lightning Conductors--Earth’s Magnetism due
  to Electrical Currents--Influence on Vitality--Animal and
  Vegetable Development--Terrestrial Currents--Electricity
  of Mineral Veins--Electrotype--Influence of Heat, Light,
  and Actinism on Electrical Phenomena                         193


  CHAPTER X.

  MAGNETISM.

  Magnetic Iron--Knowledge of, by the Ancients--Artificial
  Magnets--Electro-Magnets--Electro-Magnetism--Magneto-
  Electricity--Theories of Magnetism--The Magnetic
  Power of soft Iron and Steel--Influence of Heat
  on Magnetism--Terrestrial Magnetism--Declination
  of the Compass-needle--Variation of the
  Earth’s Magnetism--Magnetic Poles--Hansteen’s
  Speculations--Monthly and Diurnal Variation--Dip and
  Intensity--Thermo-Magnetism--Aurora Borealis--Magnetic
  Storms--Magnetic conditions of Matter--Diamagnetism, &c.     235


  CHAPTER XI.

  CHEMICAL FORCES.

  Nature’s Chemistry--Changes produced by Chemical
  Combination--Atomic Constitution of Bodies--Laws
  of Combination--Combining Equivalents--Elective
  Affinity--Chemical Decomposition--Compound Character
  of Chemical Phenomena--Catalysis or action of
  Presence--Transformation of Organic Bodies--Organic
  Chemistry--Constancy of Combining Proportions--The Law of
  Volumes, the Law of Substitutions, Isomeric States, &c.      270


  CHAPTER XII.

  CHEMICAL PHENOMENA.

  Water--Its Constituents--Oxygen--Hydrogen--Peroxide
  of Hydrogen--Physical Property of
  Water--Ice--Sea Water--Chlorine--Muriatic
  Acid--Iodine--Bromine--Compounds of Hydrogen
  with Carbon--Combustion--Flame--Safety
  Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic
  Acid--Influence of Plants on the Air--Chemical Phenomena
  of Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c.
  &c.                                                          295


  CHAPTER XIII.

  TIME.--GEOLOGICAL PHENOMENA.

  Time, an element in Nature’s Operations--Geological
  Science--Its Facts and Inferences--Nebular Hypothesis
  applied--Primary Formations--Plutonic and Metamorphic
  Rocks--Transition Series--Palæozoic Rocks--Commencement
  of Organic Arrangements--Existence of Phosphoric
  Acid in Plutonic Rocks--Fossil Remains--Coal
  Formation--Sandstones--Tertiary Formations--Eocene,
  Miocene, and Pliocene Formations--Progressive changes
  now apparent--General Conclusions--Physics applied in
  explanation                                                  332


  CHAPTER XIV.

  PHENOMENA OF VEGETABLE LIFE.

  Psychology of Flowers--Progress of Matter
  towards Organization--Vital Force--Spontaneous
  Generation--The Vegetable Cell--Simplest Development
  of Organization--The Crystal and the Cell--Primitive
  Germ--Progress of Vegetation--Influence of
  Light--Morphology--Germination--Production of Woody
  Fibre--Leaves--Chlorophylle--Decomposition of
  Carbonic Acid--Influence of Light, Heat, and Actinism
  on the Phenomena of Vegetable Life--Flowers and
  Fruits--Etiolation--Changes in the Sun’s Rays with the
  Seasons--Distribution of Plants--Electrical and Combined
  Physical Powers                                              357


  CHAPTER XV.

  PHENOMENA OF ANIMAL LIFE.

  Distinction between the Kingdoms
  of Nature--Progress of Animal
  Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent
  Animals--Annelidans--Myriapoda--Animal
  Metamorphoses--Fishes--Birds--Mammalia--Nervous
  System--Animal Electricity--Chemical Influences--Influence
  of Light on Animal Life--Animal Heat--Mechanical
  Action--Nervous Excitement--Man and the Animal Races, &c.    383


  CHAPTER XVI.

  GENERAL CONCLUSIONS.

  The Changes produced on Physical Phenomena by the Movement
  of the Solar System considered--Exertion of the Physical
  Forces through the Celestial Spaces--The Balance of
  Powers--Varieties of Matter--Extension of Matter--Theory
  of Nonentity--A Material Creation an indisputable
  fact--Advantages of the Study of Science--Conclusion         403


  INDEX.                                                       413

  BOHN’S BOOKS.

  TRANSCRIBER’S NOTE.




INTRODUCTION.


The True is the Beautiful. Whenever this becomes evident to our senses,
its influences are of a soul-elevating character. The beautiful,
whether it is perceived in the external forms of matter, associated in
the harmonies of light and colour, appreciated in the modulations of
sweet sounds, or mingled with those influences which are, as the inner
life of creation, ever appealing to the soul through the vesture which
covers all things, is the natural theme of the poet, and the chosen
study of the philosopher.

But, it will be asked, where is the relation between the stern labours
of science and the ethereal system which constitutes poetry? The fumes
of the laboratory, its alkalies and acids, the mechanical appliances of
the observatory, its specula and its lenses, do not appear fitted for
a place in the painted bowers of the Muses. But, from the labours of
the chemist in his cell,--from the multitudinous observations of the
astronomer on his tower,--spring truths which the philosopher employs
to interpret nature’s mysteries, and which give to the soul of the poet
those realities to which he aspires in his high imaginings.

Science solicits from the material world, by the persuasion of
inductive search, a development of its elementary principles, and of
the laws which these obey. Philosophy strives to apply the discovered
facts to the great phenomena of being,--to deduce large generalities
from the fragmentary discoveries of severe induction,--and thus to
ascend from matter and its properties up to those impulses which
stir the whole, floating, as it were, on the confines of sense, and
indicating, though dimly, those superior powers which, more nearly
related to infinity, mysteriously manifest themselves in the phenomena
of mind. Poetry seizes the facts of the one and the theories of the
other; unites them by a pleasing thought, which appeals for truth to
the most unthinking soul, and leads the reflective intellect to higher
and higher exercises; it connects common phenomena with exalted ideas;
and, applying its holiest powers, it invests the human mind with the
sovereign strength of the True.

Truth is the soul of the poet’s thought;--truth is the reward of the
philosopher’s toil; and their works, bearing this stamp, live among
men through all time. Science at present rejoices in her ministry to
the requirements of advancing civilization, and is content to receive
the reward given to applications which increase the comforts of life,
or add to its luxuries. Every improvement in the arts or manufactures,
beyond encreasing utilities for society, has a tendency to elevate the
race. Science is ever useful in the working days of our week, but it is
not to be neglected on our Sabbath,--when, resting from our labours,
it becomes agreeable to contemplate the few truths permitted to our
knowledge, and thus enter into communion as closely as is allowed to
finite beings, with those influences which involve and interpenetrate
the earth, giving to all things Life, Beauty, and Divinity.

The human mind naturally delights in the discovery of truth; and
even when perverted by the constant operations of prevailing errors,
a glimpse of the Real comes upon it like the smile of daylight to
the sorrowing captive of some dark prison. The Psychean labours to
try man’s soul, and exalt it, are the search for truth beneath the
mysteries which surround creation,--to gather amaranths, shining with
the hues of heaven, from plains upon which hang, dark and heavy, the
mists of earth. The poet may pay the debt of nature,--the philosopher
may return to the bosom of our common mother,--even their names fade
in the passage of time, like planets blotted out of heaven but the
truths they have revealed to man burn on for ever with unextinguishable
brightness. Truth cannot die; it passes from mind to mind, imparting
light in its progress, and constantly renewing its own brightness
during its diffusion. The True is the Beautiful; and the truths
revealed to the mind render us capable of perceiving new beauties on
the earth. The gladness of truth is like the ringing voice of a joyous
child, and the most remote recesses echo with the cheerful sound. To be
for ever true is the Science of Poetry,--the revelation of truth is the
Poetry of Science.

Man, a creation endued with mighty faculties, but a mystery to himself,
stands in the midst of a wonderful world, and an infinite variety of
phenomena arise around him in strange form and magical disposition,
like the phantasma of a restless night.

The solid rock obeys a power which brings its congeries of atoms into
a thousand shapes, each one geometrically perfect. Its vegetable
covering, in obedience to some external excitation, developes itself
in a curious diversity of forms, from the exquisitely graceful to the
singularly grotesque, and exhibits properties still more varied and
opposed. The animal organism quickened by higher impulses,--powers
working within, and modifying the influence of the external
forces,--presents, from the Monad to the Mammoth, and through every
phase of being up to Man, a yet more wonderful series of combinations,
and features still more strangely contrasted.

Lifting our searching gaze into the measureless space beyond our earth,
we find planet bound to planet, and system chained to system, all
impelled by a universal force to roll in regularity and order around a
common centre. The pendulations of the remotest star are communicated
through the unseen bond; and our rocking world obeys the mysterious
impulse throughout all those forces which regulate the inorganic
combinations of this earth, and unto which its organic creation is
irresistibly compelled to bow.

The glorious sun by day, and the moon and stars in the silence and the
mystery of night, are felt to influence all material nature, holding
the great Earth bound in a many-stranded cord which cannot be broken.
The tidal flow of the vast ocean, with its variety of animal and
vegetable life, the atmosphere, bright with light, obscured by the
storm-cloud, spanned by the rainbow, or rent with the explosions of
electric fire,--attest to the might of these elementary bonds.

These are but a few of the great phenomena which play their part around
this globe of ours, exciting men to wonder, or shaking them with terror.

The mind of man, in its progress towards its higher destiny, is tasked
with the physical earth as a problem, which, within the limits of a
life, it must struggle to solve. The intellectual spirit is capable of
embracing all finite things. Man is gifted with powers for studying
the entire circle of visible creation; and he is equal, under proper
training, to the task of examining much of the secret machinery which
stirs the whole.

In dim outshadowing, earth’s first poets, from the loveliness of
external nature, evoked beautiful spiritualizations. To them the shady
forests teemed with aërial beings,--the gushing springs rejoiced in
fantastic sprites,--the leaping cataracts gleamed with translucent
shades,--the cavernous hills were the abodes of genii,--and the
earth-girdling ocean was guarded by mysterious forms. Such were the
creations of the far-searching mind in its early consciousness of the
existence of unseen powers. The philosopher picked out his way through
the dark and labyrinthine path, between effects and causes, and slowly
approaching towards the light, he gathered semblances of the great
Reality, like a mirage, beautiful and truthful, although still but a
cloud-reflection of the vast Unseen.

It is thus that the human mind advances from the Ideal to the Real,
and that the poet becomes the philosopher, and the philosopher rises
into the poet; but at the same time as we progress from fable to
fact, much of the soul-sentiment which made the romantic holy, and
gave a noble tone to every aspiration, is too frequently merged in a
cheerless philosophy which clings to the earth, and reduces the mind
to a mechanical condition, delighting in the accumulation of facts,
regardless of the great laws by which these are regulated, and the
harmony of all Telluric combinations secured. In science we find the
elements of the most exalted poetry; and in the mysterious workings
of the physical forces we discover connections with the illimitable
world of thought,--in which mighty minds delight to try their
powers,--as strangely complicated, and as marvellously ordered, as in
the psychological phenomena which have, almost exclusively, been the
objects of their studies.

In the aspect of visible nature, with its wonderful diversity of form
and its charm of colour, we find the Beautiful; and in the operations
of these principles, which are ever active in producing and maintaining
the existing conditions of matter, we discover the Sublime.

The form and colour of a flower may excite our admiration; but when
we come to examine all the phenomena which combine to produce that
piece of symmetry and that lovely hue,--to learn the physiological
arrangement of its structural parts,--the chemical actions by which
its woody fibre and its juices are produced,--and to investigate those
laws by which is regulated the power to throw back the white sunbeam
from its surface in  rays,--our admiration passes to the higher
feeling of deep astonishment at the perfection of the processes, and
of reverence for their great Designer. There are, indeed, “tongues in
trees;” but science alone can interpret their mysterious whispers, and
in this consists its poetry.

To rest content with the bare enunciation of a truth, is to perform
but one half of a task. As each atom of matter is involved in an
atmosphere of properties and powers, which unites it to every mass of
the universe, so each truth, however common it may be, is surrounded
by impulses which, being awakened, pass from soul to soul like musical
undulations, and which will be repeated through the echoes of space,
and prolonged for all eternity.

The poetry which springs from the contemplation of the agencies which
are actively employed in producing the transformation of matter, and
which is founded upon the truths developed by the aids of science,
should be in no respect inferior to that which has been inspired by the
beauty of the individual forms of matter, and the pleasing character of
their combinations.

The imaginative view of man and his world--the creations of the
romantic mind--have been, and ever will be, dwelt on with a
soul-absorbing passion. The mystery of our being, and the mystery
of our ceasing to be, acting upon intelligences which are for ever
striving to comprehend the enigma of themselves, leads by a natural
process to a love for the Ideal. The discovery of those truths which
advance the human mind towards that point of knowledge to which all
its secret longings tend, should excite a higher feeling than any mere
creation of the fancy, how beautiful soever it may be. The phenomena
of Reality are more startling than the phantoms of the Ideal. Truth
is stranger than fiction. Surely many of the discoveries of science
which relate to the combinations of matter, and exhibit results which
we could not by any previous efforts of reasoning dare to reckon on,
results which show the admirable balance of the forces of nature, and
the might of their uncontrolled power, exhibit to our senses subjects
for contemplation truly poetic in their character.

We tremble when the thunder-cloud bursts in fury above our heads. The
poet seizes on the terrors of the storm to add to the interest of his
verse. Fancy paints a storm-king, and the genius of romance clothes
his demons in lightnings, and they are heralded by thunders. These
wild imaginings have been the delight of mankind; there is subject
for wonder in them: but is there anything less wonderful in the
well-authenticated fact, the dew-drop which glistens on the flower,
that the tear which trembles on the eye-lid, holds locked in its
transparent cells an amount of electric fire equal to that which is
discharged during a storm from a thunder-cloud?

In these studies of the effects which are continually presenting
themselves to the observing eye, and of the phenomena of causes, as far
as they are revealed by Science in its search of the physical earth,
it will be shown that beneath the beautiful vesture of the external
world there exists, like its quickening soul, a pervading power,
assuming the most varied aspects, giving to the whole its life and
loveliness, and linking every portion of this material mass in a common
bond with some great universal principle beyond our knowledge. Whether
by the improvement of the powers of the human mind, man will ever be
enabled to embrace within his knowledge the laws which regulate these
remote principles, we are not sufficiently advanced in intelligence
to determine. But if admitted even to a clear perception of the
theoretical Power which we regard as regulating the known forces, we
must still see an unknown agency beyond us, which can only be referred
to the Creator’s will.




THE POETRY OF SCIENCE.




CHAPTER I.

GENERAL CONDITIONS OF MATTER.

  Its varied Characters, and constant change of external Form--The
    Grain of Dust, its Properties and Powers--Combinations in inorganic
    Masses and in organized Creations--Our knowledge of Matter--Theory
    of Ultimate Atoms--The Physical Forces acting on the Composition of
    Masses--The certainty of the exercise of subtile principles, which
    are beyond the reach of experimental Science.


The Physical Earth presents to us, in every form of organic and
inorganic matter, an infinite variety of phenomena. If we select
specimens of rocks, either crystalline or stratified,--of metals in
any of their various combinations with oxygen, sulphur, and other
bodies,--of gems glistening with light and glowing with colour,--if
we examine the varied forms and hues of the vegetable world, or the
more mysterious animal creations, we must inevitably come to the
conclusion, long since proclaimed, and admit that dust they are, and
to dust must they return. Whatever permanency may be given to matter,
it is certain that its form is ever in a state of change. The surface
of the “Eternal Hills” is worn away by the soft rains which fall to
fertilize, and from their wrecks, borne by the waters to the ocean, new
continents are forming. The mutations of the old earth may be read upon
her rocks and mountains, and these records of former changes tell us
the infallible truth, that as the present passes into the future, so
will the form of Earth undergo an important alteration. The same forces
which lifted the Andes and the Himalayas are still at work, and from
the particles of matter carried from the present lands by the rivers
into the sea, where they subside in stratified masses, there will, in
the great future, be raised new worlds, upon which the work of life
will go forward, and over which will be spread a vast Intelligence.

If we regard the conditions of the beautiful and varied organic
covering of the Earth, the certainty, the constancy, of change is ever
before us. Vegetable life passes into the animal form, and both perish
to feed the future plant. Man, moving to-day the monarch of a mighty
people, in a few years passes back to his primitive clod, and that
combination of elementary atoms, which is dignified with the circle of
sovereignty and the robe of purple, after a period may be sought for in
the herbage of the fields, or in the humble flowers of the valley.

We have, then, this certain truth,--all things visible around us are
but aggregations of atoms. From particles of dust, which under the
microscope could scarcely be distinguished one from the other, are all
the varied forms of nature created. This grain of dust, this particle
of sand, has strange properties and powers. Science has discovered
some truths, but still more are hidden within this irregular molecule
of matter which we now survey, than have yet been shadowed in the
dreams of our philosophy. How strangely it obeys the impulses of
heat--mysterious are the influences of light upon it--electricity
wonderfully excites it--and still more curious is the manner in which
it obeys the magic of chemical force. These are phenomena which we have
seen; we know them, and we can reproduce them at our pleasure. We have
advanced a little way into the secrets of nature, and from the spot we
have gained, we look forward with a vision somewhat brightened by our
task; but we discover so much to be yet unknown, that we learn another
truth,--our vast ignorance of many things relating to this grain of
dust.

It gathers around it other particles; they cling together, and each
acting upon every other one, and all of them arranging themselves
around the little centre according to some law, a beautiful crystal
results, the geometric perfection of its form being a source of
admiration.

It exerts some other powers, and atom cohering to atom, obeying the
influences of many external radiant forces, undergoes inexplicable
changes, and the same dust which we find forming the diamond,
aggregates into the lordly tree,--blends to produce the graceful,
scented, and richly painted flower,--and combines to yield the luxury
of fruit.

It quickens with yet undiscovered energies; it moves with life: dust
is stirred by the mysterious excitement of vital force; and blood and
bone, nerve and muscle, are the results. Forces, which we cannot by
the utmost refinements of our philosophy detect, direct the whole,
and from the same dust which formed the rock and grew in the tree, is
produced a living and a breathing thing, capable of receiving a Divine
illumination, of bearing in its new state the gladness and the glory of
a Soul.

These considerations lead us to reflect on the amount of our knowledge.
We are led to ask ourselves, what do we know? We know that the world
with all its variety is composed of certain material atoms, which,
although presented to us in a great variety of forms, do not in all
probability differ very essentially from each other.

We know that those atoms obey certain conditions which appear to be
dependent upon the influences of motion, gravitation, heat, light,
electricity, and chemical force. These powers are only known to us
by their effects; we only detect their action by their operations
upon matter; and although we regard the several phenomena which we
have discovered, as the manifestations of different principles, it is
possible they may be but modifications of some one universal power, of
which these are but a few of its modes of action.

In examining, therefore, the truths which science has revealed to us,
it is advantageous, for the purpose of fixing the mind to the subject,
that we assume certain conditions as true. These may be stated in a few
sentences, and then, without wasting a thought upon those metaphysical
subtleties which have from time to time perplexed science, and served
to impede the progress of truth, we shall proceed to examine our
knowledge of the phenomena which constantly occur around us.

Every form, whether inorganic or organic, which we can discover within
the limits of human search, is composed of atoms, which are capable of
assuming, under the influence of certain physical forces, conditions
essential to the physical state of that body of which they constitute
a part.[1] The known forces, active in producing these conditions,
are modes of motion; gravitation and aggregation, heat, light; and
associated with these, actinism or chemical radiation; electricity,
under all its conditions, whether static or dynamic; and chemical
affinity, regarded as the result of a separate elementary principle.

These forces must be considered as powers capable of acting in perfect
independence of each other. They are possibly modifications of one
principle; but this view being an hypothesis, which, as yet, is only
supported by loose analogies, cannot, without danger, be received in
any explanation which attempts to deal only with the truths of science.

We cannot examine the varied phenomena of nature, without feeling that
there must be other and most active principles of a higher order than
any detected by science, to which belong the important operations of
vitality, whether manifested in the plant or the animal. In treating
of these, although speculation cannot be entirely avoided, it will be
employed only so far as it gives any assistance in linking phenomena
together.

We have to deal with the active agencies which give form and feature to
nature--which regulate the harmony and beauty and vigour of life--and
upon which depend those grand changes in the conditions of matter,
which must convince us that death is but the commencement of a new
state of being.


FOOTNOTES:

[1] Sir Isaac Newton supposed matter to consist of hard, impenetrable,
perfectly inelastic atoms.

Boscovich regarded the constitution of matter differently. The ultimate
atom was with him a point surrounded by powers of infinite elasticity.
(See _Dr. Robisons Mechanical Philosophy_, for a full explanation of
the theory of Boscovich.)

The view entertained by Dr. Faraday, which will be comprehended from
one or two short extracts from his valuable and suggestive paper,
claims attention:--

“If the view of the constitution of matter already referred to be
assumed to be correct--and I may be allowed to speak of the particles
of matter, and the space between them (in water, or in the vapour
of water, for instance), as two different things--the space must be
taken as the only continuous part, for the particles are considered
as separated by space from each other. Space will permeate all masses
of matter in every direction like a net, except that in the place of
meshes it will form cells, isolating each atom from its neighbours, and
itself only being continuous.”

Examining the question of the conducting power of different bodies,
and observing that as space is the only continuous part, so space,
according to the received view of matter, must be at one time a
conductor, at others a non-conductor, it is remarked:

“It would seem, therefore, that, in accepting the ordinary atomic
theory, space may be proved to be a non-conductor in non-conducting
bodies, and a conductor in conducting bodies; but the reasoning ends
in this--a subversion of that theory altogether; for, if space be
an insulator, it cannot exist in conducting bodies; and if it be a
conductor, it cannot exist in insulating bodies.”--_A Speculation
touching Electric Conduction, and the Nature of Matter_: by Michael
Faraday, D.C.L., F.R.S., &c.: Philosophical Magazine, vol. xxiv. Third
Series.

See also Wollaston, _On the Finite Extent of the Atmosphere_.--Phil.
Trans. 1822. Young, _On the Essential Properties of Matter_.--Lectures
on Natural Philosophy. Mossotti, _On Molecular Action_.--Scientific
Memoirs, vol. i. p. 448.




CHAPTER II.

MOTION.

  Are the Physical Forces modes of Motion?--Motion
    defined--Philosophical Views of Motion, and the Principles to
    which it has been referred--Motions of the Earth and of the Solar
    System--Visible Proofs of the Earth’s Motion on its Axis--Influence
    of the proper Motions of the Earth on the Conditions of
    Matter--Theory of the Conversion of Motion into Heat, &c.--The
    Physical Forces regarded as principles independent of Motion,
    although the Cause and often apparently the Effects of it.


Many of the most eminent thinkers of the present time are disposed to
regard all the active principles of nature as “modes of motion,”--to
look upon light, heat, electricity, and even vital force, as phenomena
resulting from “change of place” among the particles of matter; this
change, disturbance, or motion, being dependent upon some undefined
mover.[2]

The habit of leaving purely inductive examination for the delusive
charms of hypothesis--of viewing the material world as a metaphysical
bundle of essential properties, and nothing more--has led some eminent
philosophers to struggle with the task of proving that all the
wonderful manifestations of the great physical powers of the universe
are but modifications of motion, without the evidence of any antecedent
force.[3]

The views of metaphysicians regarding motion involve many subtle
considerations which need not at present detain us. We can only
consider motion as a change of place in a given mass of matter. Now
matter cannot effect this of itself, no change of place being possible
without a mover; and, consequently, motion cannot be a _property_ of
matter, in the strict sense in which that term should be accepted.[4]

Motion depends upon certain external disturbing and directing forces
acting upon all matter; and, consequently, as every mode of action
is determined by some excitement external to the body moved, motion
cannot, philosophically, be regarded otherwise than as a peculiar
affection of matter under determinable conditions. “We find,” says Sir
Isaac Newton, “but little motion in the world, except what plainly
flows from either the active principles of nature, or from the command
of the willer.”[5]

Plato, Aristotle, and the Pythagoreans, supposed that throughout all
nature an active principle was diffused, upon which depended all the
properties exhibited by matter. This is the same as the “plastic
nature” of Cudworth,[6] the “intellectual and artificial fire” of
Bishop Berkeley;[7] and to these all modes of motion were referred.
Sir Isaac Newton also regards the material universe and its phenomena
as dependent upon “_active principles_”--for instance, the cause of
gravity--whereby the planets and comets preserve their motions in their
orbits, and all bodies acquire a degree of motion in falling; and the
cause of fomentation--whereby the heart and blood of animals preserve
a perpetual warmth and motion--the inner parts of the earth are kept
constantly warmed--many bodies burn and shine--and the sun himself
burns and shines, and with his light warms and cheers all things.

The earth turns on its axis at the rate of more than 1,000 miles an
hour, and passes around the sun with the speed of upwards of 68,000
miles in the same time.[8] The earth and the other planets of our
system move in ellipses around a common centre: therefore their motion
cannot have been originally communicated merely by the impressed force
of projection. Two forces, at least, must have operated, one making
the planets tend directly to the centre, and the other impelling them
to fly off at a tangent to the curve described. Here we have a system
of spheres, held by some power to a great central mass, around which
they revolve with a fearful velocity. Nor is this all; the Solar System
itself, bound by the same mystic chain to an undiscovered centre, moves
towards a point in space at the rate of 33,550,000 geographical miles,
whilst our earth performs one revolution around the sun.[9]

The evidence of the motion of the Earth around its axis, as afforded
by the swinging of a pendulum or the rotation of a sphere, is too
interesting to be omitted. In mechanical philosophy, we have two
terms of the same general meaning--the conservation of the plane
of vibration--and the conservation of the axis of rotation. For
the non-scientific reader, these terms require explanation, and in
endeavouring to simplify this as much as possible, we must ask the
indulgence of the Mechanical Philosopher. Let us fix in the centre
of a small round table an upright rod, having an arm extending from
its top, to which we can suspend a tolerably heavy weight attached
to a string. This is our piece of apparatus: upon the table draw a
chalk line, along which line we intend our pendulum to swing, and
continuing this line upon the floor, or by a mark on the wall, our
arrangements are complete. Raise steadily the bob of our pendulum,
and set it free, so that its plane of vibration is along the line
which has been marked. As the pendulum is swinging firmly along this
line, slowly and steadily turn the table round. It will then be seen
that the pendulum will still vibrate in the direction of the line we
have continued onward to the wall, but that the line on the table is
gradually withdrawn from it. If we had no upright, we might turn the
table entirely round, without in the slightest degree altering the
line along which the pendulum performs its oscillations. Now, if from
some elevated spot, say, from the centre of the dome of St. Paul’s,
a long and heavy pendulum is suspended, and if on the floor we mark
the line along which we set the pendulum free to vibrate, it will be
seen, as in the experiment with the table, that the marked line moves
away from under the pendulum. It continues to vibrate in the plane it
first described, although the line on the earth’s surface continues
to move forward by the diurnal rotation around the axis. Similar to
this is the law of the conservation of the axis of rotation. If a
common humming-top, the spindle of which is its axis of rotation, is
set spinning obliquely, it will be seen that the axis will continue
to point along the line it took at the commencement of motion. By
placing a heavy sphere in a lathe, resting its projecting axial points
on some moveable bearings, and then getting the sphere into extremely
rapid motion, one of the bearings may be removed without the mass
falling to the ground. The rapidity of motion changes so constantly and
quickly the position of the particles which have a tendency to fall,
that we have motion balanced against the force of gravitation in a
striking manner; and we learn, from this experiment, the explanation
of the planetary and stellar masses revolving on their axis at a speed
sufficient to maintain them without support in space. A mass of matter,
a sphere or a disc, carefully balanced, is fixed in gymbals such as we
employ for fixing our compass needles, and it is set by some mechanical
contrivance in rapid rotation. The position of the axis of rotation
remains unaltered, although the earth is moving; and thus, by this
instrument,--called the gyroscope,--we can determine, as with the
pendulum, the motion of the earth around its axis; and we learn why,
during its movement around the sun, its axis is undeviatingly pointed
towards one point in space, marked in our Heavens as the Polar Star.

In addition to these great rotations, the earth is subjected to other
motions, as the precession of the equinoxes and the nutation of its
axis. Rocking regularly upon a point round which it rapidly revolves,
whilst it progresses onward in its orbit, like some huge top in
tremulous gyration upon the deck of a vast aërial ship gliding rapidly
through space, is the earth performing its part in the great law of
motion.

The rapidity of these impulses, supposing the powers of the physical
forces were for a moment suspended, would be sufficient to scatter the
mass of our planet over space as a mere star-dust.

Limiting, as much as possible, the view which opens upon the mind as we
contemplate the adjustments by which this great machine, our system, is
preserved in all its order and beauty, let us forget the great movement
of the whole through space, and endeavour to consider the effect of
those motions which are directly related to the earth, as a member of
one small group of worlds.

We cannot for a moment doubt, although we have not any experimental
proof of the fact, that the proper motions of the earth materially
influence the conditions of the matter of which it is formed. Every
pair of atoms is, like a balance, delicately suspended, under the
constant struggle which arises from the tendency to fly asunder,
induced by one order of forces--centrifugal force--and the efforts of
others, gravitation and cohesion, to chain them together. The spring is
brought to the highest state of tension--one tremor more, and it would
be destroyed.

We cannot, by any comparison with the labours of the most skilful human
artisan, convey an idea of the exquisite perfection of planetary
mechanics, even so far as they have been discovered by the labours of
science; and we must admit that our insight into the vast machinery has
been very limited.

All we know is the fact that this planet moves in a certain order, and
at a fixed rate, and that the speed is of itself sufficient to rend
the hardest rocks; yet the delicate down which rests so lightly upon
the flower is undisturbed. It is, therefore, evident that matter is
endued with powers, by which mass is bound to mass, and atom to atom;
these powers are not the results of any of the motions which we have
examined, but, acting in antagonism to them, they sustain our globe in
its present form.

Are there other motions to which these powers can be referred? We
know of none. That absolute rest may not exist among the particles of
matter is probable. Electrical action, chemical power, crystalline
aggregation, the expansive force of heat, and many other known
agencies, are in constant operation to prevent it. It must, however,
be remembered, that each and every atom constituting a mass may be
so suspended between the balanced forces, that it may be regarded as
relatively at rest.

Theory imagines Motion as producing Force--a body is moved, and its
mere mechanical change of place is regarded as generating heat; and
hence the refinements of modern science have advanced to the conclusion
that motion and heat are convertible. Admitting that the material atoms
of which this world is formed are never in a state of quiescence, yet
we cannot suppose any gross ponderable particle as capable of moving
itself; but once set in motion, it may become the secondary cause of
motion in other particles.[10] The difficulties of the case would
appear to have been as follows:--Are heat, light, electricity, &c.,
material bodies? If they are material bodies--and heat, for example, is
the cause of motion--must not the calorific matter move itself--or if
it be not self-moving, by what is it moved? If heat is material, and
the primary cause of motion, then matter must have an innate power of
moving; it can convert itself into active force, or be at once a cause
and an effect, which can scarcely be regarded as a logical deduction.

We move a particle of matter, and heat is manifested; the force being
continued, light, electricity, and chemical action result; all,
as appears from a limited view of the phenomena, arising out of
the mechanical force applied to the particle first moved.[11] This
mechanical force, it must be remembered, is external to the body moved,
and is, in all probability, set up by the movement of a muscle, acted
upon by nerves, under the influence of a will.

The series of phenomena we have supposed to arise admit of an
explanation free of the hypothesis of motion, and we avoid the
dangerous ground of metaphysical speculation, and the subtleties of
that logic which rests upon the immateriality of all creation. This
explanation, it is freely admitted, is incomplete: we cannot distinctly
correlate each feature of the phenomena, combine link to link, and thus
form a perfect chain; but it is sufficiently clear to exhibit what we
do know, and leave the unknown free for unbiassed investigation.

Each particle, each atom of that which conveys to our senses the only
ideas we have of natural objects--ponderable matter--is involved
in, or interpenetrated by, those principles which we call heat and
electricity, with probably many others which are unknown to us; and
although these principles or powers are, according to some law, bound
in statical equilibrium to inert matter, they are freely developed
by an external excitement, and the disturbance of any one of them,
upsetting the equilibrium, leaves the other power equally free to be
brought under the cognizance of human sense by their effects.

When we come to an examination of the influences exerted by these
powers upon the physical earth, the position, that they must be
regarded as the causes of motion rather than the effects of it, will
be further considered. At present it is only necessary to state
thus generally the views we entertain of the conditions of matter
in connection with the imponderable forces and mechanical powers.
The conversion, as it has been called, of motion into heat, in the
experiments of Count Rumford and Mr. Joule,[12] are only evidences that
a certain uniformity exists between the mechanical force applied, and
the amount of heat liberated. It does not appear that we have any proof
of the conversion of motion into physical power.

It is necessary, to a satisfactory contemplation of the wonderful
properties of matter, and of the forces regulating the forms of
the entire creation, that we should be content with regarding the
elementary bodies which chemistry instructs us form our globe, as
tangible, ponderable atoms, having specific and distinguishing
properties. That we should, as far as it is possible for finite minds
to do so, endeavour to conceive the powers or forces--gravitation,
molecular attraction, electricity, heat, light, and the principle which
determines all chemical phenomena--as manifestations of agencies which
hold a place between the most subtile form of matter and the hidden
principles of vitality, which is still vastly inferior to the spiritual
state, which reveals itself dimly in psychological phenomena, and
arrives at its sublimity in the God of the universe.


FOOTNOTES:

[2] “Motion, therefore, is a change of rectilinear distance between
two points. Allowing the accuracy of this definition, it appears that
two points are necessary to constitute motion; that in all cases, when
we are inquiring whether or no any body or point is in motion, we must
recur to some other point which we can compare with it; and that if a
single atom existed alone in the universe, it could neither be said to
be in motion nor at rest.

“The space which we call quiescent is in general the earth’s surface;
yet we well know, from astronomical considerations, that every point of
the earth’s surface is perpetually in motion, and that in very various
directions: nor are any material objects accessible to our senses which
we can consider as absolutely motionless, or even as motionless with
regard to each other; since the continual variation of temperature to
which all bodies are liable, and the minute agitations arising from the
motion of other bodies with which they are connected, will always tend
to produce some imperceptible changes in their distances.”--_Lectures
on Natural Philosophy, &c._, by Thomas Young, M.D. Edited by the Rev.
P. Kelland. 1845.

[3] “The position which I seek to establish in this essay is, that
the various imponderable agencies, or the affections of matter which
constitute the main objects of experimental physics, viz., heat,
light, electricity, magnetism, chemical affinity, and motion, are all
correlative, or have a reciprocal dependence;--that neither, taken
abstractedly, can be said to be the essential or proximate cause of the
others; but that either may, as a force, produce, or be convertible
into, the other:--thus heat may mediately or immediately produce
electricity, electricity may produce heat, and so of the rest....
Although strongly inclined to believe that the five other affections of
matter, which I have above named, are, and will ultimately be, resolved
into modes of motion, it would be going too far at present to assume
their identity with it: I, therefore, use the term force, in reference
to them, as meaning that active force inseparable from matter, which
induces its various changes.”--_On the Correlation of Physical Forces_,
by W. R. GROVE, Esq., M.A., F.R.S.

[4] When discussing the hypothesis of Hobbes--_that no body can
possibly be moved but by a body contiguous and moved_--Boyle asks:--

“I demand how there comes to be local motion in the world? For either
all the portions of matter that compose the universe have motion
belonging to their natures, which the Epicureans affirmed for their
atoms, or some parts of matter have this motive power, and some have
not, or else none of them have it; but all of them are naturally
devoid of motion. If it be granted that motion does naturally belong
to all parts of matter, the dispute is at an end, the concession quite
overthrowing the hypothesis.

“If Mr. Hobbes should reply that the motion is impressed upon any of
the parts of matter by God, he will say that which I most readily grant
to be true, but will not serve his turn, if he would speak congruously
with his own hypothesis. For I demand whether this Supreme Being
that the assertion has recourse to, be a corporeal or an incorporeal
substance? If it be the latter, and yet the efficient cause of motion
in bodies, then it will not be universally true that whatever body is
moved is so by a body contiguous and moved. For, in our supposition,
the bodies that God moves, either immediately or by the intervention
of any other immaterial being, are not moved by a body contiguous,
but by an incorporeal spirit.”--_Some Considerations about the
Reconcileableness of Reason and Religion_: Boyle, vol. iii. p. 520.

[5] Boyle has some ingenious speculations on this point:--

“That there is local motion in many parts of matter is manifest to
sense, but how matter came by this motion was of old, and is still,
hotly disputed of: for the ancient Corpuscularian philosophers (whose
doctrine in most other points, though not in all, we are the most
inclinable to), not acknowledging an author of the universe, were
thereby reduced to make motion congenite to matter, and consequently
coeval with it. But since local motion, or an endeavour at it, is not
included in the nature of matter, which is as much matter when it rests
as when it moves; and since we see that the same portion of matter may
from motion be reduced to rest, and after it hath continued at rest, so
long as other bodies do not put it out of that state, may by external
agents be set a moving again; I, who am not wont to think a man the
worse naturalist for not being an atheist, shall not scruple to say
with an eminent philosopher of old, whom I find to have proposed among
the Greeks that opinion (for the main) that the excellent Des Cartes
has revived amongst us, that the origin of motion in matter is from
God; and not only so, but that thinking it very unfit to be believed,
that matter barely put into motion, and then left to itself, should
casually constitute this beautiful and orderly world; I think also
further, that the wise Author of things did, by establishing the laws
of motion among bodies, and by guiding the first motions of the small
parts of matter, bring them to convene after the manner requisite
to compose the world; and especially did contrive those curious and
elaborate engines, the bodies of living creatures, endowing most of
them with the power of propagating their species.”--_Considerations and
Experiments touching the Origin of Forms and Qualities_: Boyle’s Works,
vol. ii. p. 460. Edinburgh. 1744.

[6] Cudworth’s _Intellectual System_.

[7] “According to the Pythagoreans and Platonists, there is a life
infused throughout all things ... an intellectual and artificial
fire--an inward principle, animal spirit, or natural life, producing
or forming within, as art doth without--regulating, moderating, and
reconciling the various motions, qualities, and parts of the mundane
system. By virtue of this life, the great masses are held together in
their ordinary courses, as well as the minutest particles governed in
their natural motions, according to the several laws of attraction,
gravity, electricity, magnetism, and the rest. It is this gives
instincts, teaches the spider her web, and the bee her honey;--this
it is that directs the roots of plants to draw forth juice from the
earth, and the leaves and the cortical vessels to separate and attract
such particles of air and elementary fire as suit their respective
natures.”--Bishop Berkeley, _Siris_, No. 277.

[8] “The revolution of the earth is performed in a natural day,
or, more strictly speaking, once in 23h. 56' 4", and as its mean
circumference is 24,871 miles, it follows that any point in its
equatorial surface has a rotatory motion of more than 1,000 miles per
hour. This velocity must gradually diminish to nothing at either pole.
Whilst the earth is thus revolving on its axis, it has a progressive
motion in its orbit. If we take the length of the earth’s orbit at
630,000,000, its motion through space must exceed 68,490 miles in the
hour.”--Enc. Brit. art. _Physical Geography_.

[9] “Here then we have the splendid result of the united studies of
MM. Argelander, O. Struve, and Peters, grounded on observations made
at the three observatories of Dorpat, Abo, Pulkova, and which is
expressed in the following thesis:--The motion of the solar system in
space is directed to a point of the celestial vault situated on the
right line which joins the two stars π and μ _Herculis_, at a quarter
of the apparent distance of these stars, reckoning from π _Herculis_.
The velocity of this motion is such, that the sun, with all the bodies
which depend upon it, advances annually in the above direction 1·623
times the radius of the earth’s orbit, or 33,550,000 geographical
miles. The possible error of this last number amounts to 1,733,000
geographical miles, or to a _seventh_ of the whole value. We may then
wager 400,000 to 1 that the sun has a proper progressive motion, and
1 to 1 that it is comprised between the limits of thirty-eight and
twenty-nine millions of geographical miles.”--_Etudes d’Astronomie
Stellaire: Sur la Voie Lactée et sur les Distances des Etoiles Fixes_:
M. F. W. G. Struve. [A report addressed to his Excellency M. Le Comte
Ouvaroff; Minister of Public Instruction and President of the Imperial
Academy of Sciences at St. Petersburg.]

[10] “The first great agent which the analysis of natural phenomena
offers to our consideration, more frequently and prominently than
any other, is force. Its effects are either, 1st, to counteract the
exertion of opposing force, and thereby to maintain _equilibrium_; or,
2ndly, to produce _motion_ in matter,

“Matter, or that whatever it be of which all the objects in nature
which manifest themselves directly to our senses consist, presents us
with two general qualities, which at first sight appear to stand in
contradiction to each other--activity and inertness. Its activity is
proved by its power of spontaneously setting other matter in motion,
and of itself obeying their mutual impulse, and moving under the
influence of its own and other force; inertness, in refusing to move
unless obliged to do so by a force impressed externally, or mutually
exerted between itself and other matter, and by persisting in its state
of motion or rest unless disturbed by some external cause. Yet, in
reality, this contradiction is only apparent. Force being the cause,
and motion the effect produced by it on matter, to say that matter is
inert, or has _inertia_, as it is termed, is only to say that the cause
is expended in producing its effect, and that the same cause cannot
(without renewal) produce double or triple its own proper effect.
In this point of view, equilibrium may be conceived as a continual
production of two opposite effects, each, undoing at every instant what
the other has done,”?--See continuation of the argument in _Herschel’s
Discourse on the Study of Natural Philosophy_, page 223.

In the Edinburgh New Philosophical Journal, vol. xlv., will be found a
paper by Dr Robert Brown--“_Of the sources of motions upon the Earth,
and of the means by which they are sustained_,” which will well repay
an attentive perusal, as pointing to a class of investigation of the
highest order, and containing deductions of the most philosophic
description.

[11] Friction, it is well known, generates heat; by rapidly rubbing two
sticks together, the Indian produces their ignition; heat and light
being both manifested. Under every mechanical disturbance electrical
changes can be detected, and the action of heat in the combustion of
the wood is a chemical phenomenon.

[12] Count Rumford’s experiment consisted in placing a mass of metal
in a box of water at a known temperature, and, by employing a boring
apparatus, ascertaining carefully the increase of heat after a given
number of revolutions. He thus describes his most satisfactory
experiment:--

“Everything being ready, I proceeded to make the experiment I had
projected, in the following manner. The hollow cylinder having been
previously cleaned out, and the inside of its bore wiped with a clean
towel till it was quite dry, the square iron bar, with the blunt steel
borer fixed to the end of it, was put into its place; the mouth of the
bore of the cylinder being closed at the same time by means of the
circular piston through the centre of which the iron bar passed.

“This being done, the box was put in its place; and the joinings of
the iron rod, and of the neck of the cylinder with the two ends of
the box, having been made water-tight, by means of collars of oiled
leather, the box was filled with cold water (viz., at the temperature
of 60°) and the machine was put in motion. The result of this beautiful
experiment was very striking, and the pleasure it afforded me amply
repaid me for all the trouble I had had, in contriving and arranging
the complicated machinery used in making it. The cylinder, revolving
at the rate of about thirty-two times in a minute, had been in motion
but a short time, when I perceived, by putting my hand into the water
and touching the outside of the cylinder, that heat was generated, and
it was not long before the water which surrounded the cylinder began
to be sensibly warm. At the end of one hour, I found, by plunging a
thermometer into the water in the box (the quantity of which fluid
amounted to 18·77 lbs. avoirdupois, or 2-1/4 wine gallons), that
its temperature had been raised no less than 47°; being now 107° of
Fahrenheit’s scale. When thirty minutes more had elapsed, or one hour
and thirty minutes after the machinery had been put in motion, the heat
of the water in the box was 142°. At the end of two hours, reckoning
from the beginning of the experiment, the temperature of the water
was found to be raised to 178°. At two hours twenty minutes it was at
200°; and at two hours thirty minutes it _actually boiled_.”--_Inquiry
concerning the Source of the Heat excited by Friction_: Philosophical
Transactions, vol. lxxxviii. A.D. 1798.

“Mr. Joule brought a communication on the same subject before the
British Association at Cambridge, which was afterwards published in the
Philosophical Magazine, and from that journal the following notices are
extracted:--

“The apparatus exhibited before the Association consisted of a brass
paddle-wheel, working horizontally in a can of water. Motion could
be communicated to this paddle by means of weights, pulleys, &c. The
paddle moved with great resistance in the can of water, so that the
weights (each of four pounds) descended at the slow rate of about one
foot per second. The height of the pulleys from the ground was twelve
yards, and consequently when the weights had descended through that
distance they had to be wound up again in order to renew the motion of
the paddle. After this operation had been repeated sixteen times, the
increase of the temperature of the water was ascertained by means of a
very sensible and accurate thermometer.

“A series of nine experiments was performed in the above manner, and
nine experiments were made in order to eliminate the cooling or heating
effects of the atmosphere. After reducing the result to the capacity
for heat of a pound of water, it appeared that for each degree of heat
evolved by the friction of water, a mechanical power equal to that
which can raise a weight of 890 lbs. to the height of one foot, had
been expended.

“Any of your readers who are so fortunate as to reside amid the
romantic scenery of Wales or Scotland could, I doubt not, confirm my
experiments by trying the temperature of the water at the top and at
the bottom of a cascade. If my views be correct, a fall of 817 feet
will of course generate one degree of heat, and the temperature of the
river Niagara will be raised about one fifth of a degree by its fall of
160 feet.”--_Relation between Heat and Mechanical Power_: Philosoph.
Mag. vol. xxvii. 1845.




CHAPTER III.

GRAVITATION.

  The Forms of Matter--Shape of the Earth--Probability of the Mass
    forming this Planet having existed in a Nebulous State--Zodiacal
    Lights--Comets--Volatilization of Solid Matter by Artificial
    means--The principle of Gravitation--Its Influence through
    Space and within the smallest Limits--Gravitating powers of the
    Planets--Density of the Earth--Certainty of Newton’s Law of the
    Inverse Square--Discovery of Neptune--State of a Body relieved from
    Gravitation--Experiment explaining Saturn’s Ring, &c.--General
    inference.


Let us suppose the earth--consisting of three conditions of matter;
the solid, the fluid, and the aëriform--to be set free from that power
by which it is retained in its present form of a spheroid flattened
at the poles, but still subject to the influences of its diurnal and
annual rotations. Agreeably to the law which regulates the conditions
of all bodies moving at high velocities, the consequence of such a
state of things would be, that our planet would instantly spread itself
over an enormous area. The waters and even the solid masses of this
globe would, in all probability, present themselves amidst the other
phenomena of space in a highly attenuated state, revolving in an orbit
around the sun, as a band of nebulous matter, which might sometimes
be rendered sensible to sight by still reflecting solar light, or by
condensation in the form of flights of shooting stars.[13]

This may be illustrated by experiment. If upon a rapidly revolving
disc we place a ball of dust, it will be almost immediately spread
out, and its particles will arrange themselves in a series of regular
curves, varying with the velocity of the motion. In addition to the
disintegration which would arise from the tendency of the atoms to fly
from the centre, the motion, in space, of the planetary mass would
naturally occasion a trailing out, and the only degree of uniformity
which this orb could, under these imaginary conditions, possibly
present, would be derived from the combined effects of motions in
different directions.

Amid the remoter stars, some remarkable cloud-like appearances are
discovered. These nebulæ, presenting to the eye of the observer
only a gleaming light, as from some phosphorescent vapour, were
long regarded as indications of such a condition as that which we
have just been considering. Astronomers saw, in those mysterious
nebulæ, a confirmation of their views, which regarded all the orbs
of the firmament as having once been thin sheets of vapour, which
had gradually, from irregular bodies traversing space, been slowly
condensed about a centre, and brought within the limits of aggregating
agencies, until, after the lapse of ages, they become sphered stars,
moving in harmony amid the bright host of heaven.[14] Geologists seized
on those views with eagerness, as confirming theoretical conclusions
deduced from an examination of the structure of the earth itself, and
explained by them the gradual accretion of atoms into crystalline rocks
from a cooling mass.

The researches of modern astronomers, aided by the magnificent
instruments of Lord Rosse,[15] have, however, shown that many of the
most remarkable nebulæ are only clusters of stars; so remote from
us, that the light from them appears blended into one diffused sheet
or luminous film. There are, however, the Magellanic clouds, and
other singular patches of light, exhibiting changes which can only
be explained on the theory of their slow condensation. There is no
evidence to disprove the position that world-formation may still be
going on; that a slow and gradual aggregation of particles, under the
influence of laws with which we are acquainted, may be constantly in
progress, to end, eventually, in the formation of a sphere.

May we not regard the zodiacal light as the remains of a solar
luminiferous atmosphere, which once embraced the entire system of which
it is the centre?[16] Will not the strange changes which have been
_seen to take place_ in cometary bodies, even whilst they were passing
near the earth,--as the division of Biela’s comet and the ultimate
formation of a second nucleus from the detached portion,--strongly
tend to support the probability of the idea that attenuated matter
has, in the progress of time, been condensed into solid masses, and
that nebulous clouds must still exist in every state of tenuity in the
regions of infinite space,[17] which, in the mysterious processes of
world-formation, will, eventually, become stars, and reflect across
the blue immensity of heaven, in brightness, that light which is the
necessary agent of organisation and all manifestations of beauty?

The inferences drawn from a careful study of the condition of our own
globe are in favour of the assumption of the existence of nebulous
matter. By the processes of art and manufacture, by the operation of
those powers on which organisation and life depend, solid matter is
constantly poured off in such a state that it cannot be detected, _as
matter_, by any of the human senses. Yet a thousand results, daily and
hourly accumulating as truths around us, prove that the solid metals,
the gross earths, and the constituents of animal and vegetable life,
all pass away invisible to us, and become “thin air.” We know that,
floating around us, these volatilized bodies exist in some material
form, and numerous experiments in chemistry are calculated to convince
us, that the most attenuated air is capable, with a slight change
of circumstances, of being converted into the condition of solid
masses. Hydrogen gas, the lightest, the most ethereal of the chemical
elements, dissolves iron and zinc, arsenic, sulphur, and carbon; and
from the transparent combinations thus formed, we can with facility
separate those ponderous bodies. Such substances must exist in our
own atmosphere; why not in the regions of space? Whether this planet
ever floated a mass of nebulous matter, only known by its dim and
filmy light, or comet-like rushed through space with widely eccentric
orbit, are questions which can only receive the reply of speculative
minds. Whether the earth and the other members of the Solar System were
ever parts of a Central Sun,[18] and thrown from it by some mighty
convulsion, though now revolving with all the other masses around that
orb, chained in their circuits by some infinite power, is beyond the
utmost refinements of science to discover. This hypothesis is, however,
in its sublime conception, worthy of the master-mind that gave it birth.

All we know is, that our earth is an oblate sphere, which, by the
effects of its rotation around an axis, is somewhat enlarged at the
equator and flattened at the poles;--that it maintains its regular
course around the sun, in virtue of the operation of two forces, one
of which, acting constantly, would eventually draw it into the body
of the sun itself; but that it is opposed by the other, centrifugal
force, and the varying momentum of the revolving mass;--that the same
force acting from the centre of the earth itself, and from the centre
of every particle of its substance, resolves the whole into a globular
form.

The principle of Gravitation[19] is that force which resides in every
form of matter, by which particle is attracted by particle, and mass
by mass, the less towards the greater. What this may be, we scarcely
dare to speculate. In the vast area of its action, which opens before
the eye of the mind, we see a power spanning all space, and linking
together every one of those myriads of worlds which spangle the robe
of the Infinite, and we are compelled to pause. Is this principle of
gravitation a property of matter, or is it a power higher than the
more tangible forces, is the question which presses on the mind. If
we regard it as a subtile principle pervading all space, we compel
ourselves to look beyond it for another power yet more refined; and we
cannot halt until, ascending from the limitable to the illimitable, we
resolve gravitation and its governing influences to the centre of all
power--the will of the eternal Creator.

Science has developed the grand truth, that it is by the exercise
of this all-pervading influence that the earth is retained in its
orbit--that the pellucid globe of dew which glistens on the leaf is
bound together--that the débris which float upon the lake accumulate
into one mass--that the sea exhibits the phenomena of the tides--and
the aërial ocean its barometric changes. In all things this force is
active, and throughout nature it is ever present. Our knowledge of the
laws which it obeys, enables us to conclude that the sun and distant
planets are consolidated masses like this earth. We find that they have
gravitating power, and by comparing this influence with that exerted
by the earth, we are enabled to weigh the mass of one planet against
another. In the balance of the astronomer, it is as easy to poise the
remote star, as it is for the engineer to calculate the weight of the
iron tunnel of the Menai Straits, or any other mechanical structure.
Thus throughout the universe the balance of gravitating force is
unerringly sustained. If one of the most remote of those gems of light,
which flicker at midnight in the dark distance of the starry vault,
was, by any power, removed from its place, the disturbance of these
delicately balanced mysteries would be felt through all the created
systems of worlds.

From the peculiarity of the laws which this power called gravity obeys,
it has been inferred that it acts from centres of force; it is proved
that its power diminishes in the inverse ratio of the square of the
distance, and that the gravitating power of every material body is in
the direct proportion of its mass. In astronomical calculations we have
first to learn the mass of our earth. Experiment informs us that the
density of our hardest rock is not above 2·8; but from the enormous
pressure to which matter must be subjected, at great depths from the
surface, the weight of the superincumbent mass constantly increasing,
it is quite certain that the earth’s density must be far more than
this. Maskelyne determined the attraction of large masses by a plummet
and line on the mountain Schehallion.[20] Cavendish, with exceedingly
delicate apparatus, observed the attraction of masses of known
weight and size upon each other. Applying the powers of arithmetical
calculation, and the data obtained from the small experiments to the
larger phenomena, Maskelyne determined the earth’s mean density to
be 4·71, whilst Cavendish made it 5·48, but the more recent refined
investigations of Baily have determined it to be 5·67.[21]

From data thus obtained by severe inductive experiments and
mathematical analyses, the astronomer, by observing the deviations of
a distant star, is enabled to determine the influence of those stellar
bodies near which it passes, and, hence, to calculate the relative
magnitudes of each. The accuracy of the law is in this way put to the
severest test, and the precision of astronomical prediction is the
strongest proof of its universality and truth.

Rolling onward its lonely way, in the far immensity of our system,
the planet Uranus was discovered by the elder Herschel,--so great
its distance that its diminished light could scarcely be detected
by the most powerful telescopes; but since its discovery its path
has been carefully watched, and some irregularities noticed. Most
of these disturbances were referable to known causes; but a little
alteration in its rate of motion observed when the planet was in one
portion of its vast orbit was unexplained. Convinced of the certainty
of Newton’s law, and having determined that the attraction of known
masses was insufficient to produce the disturbance observed, these
deviations were referred to the gravitating influence of a mass
beyond the known limits of our Solar System. By the investigations
of Adams in England,[22] and Le Verrier in France,[23] the place of
the hypothetical mass was determined, and its size computed. As a
grand confirmation of the great law, and to the glory of those two
far-searching minds, who do honour to their respective countries and
their age, the hypothesis became a fact, in the discovery of the planet
Neptune in the place determined by rigorous calculation. Astronomy
affords other examples of the sublime truth of the law of gravitation,
than which science can afford no more elevated poetry.

So completely is all nature locked in the bonds of this infinite power,
that it is no poetic exaggeration to declare, that the blow which rends
any earthly mass is conveyed by successive impulses to every one of the
myriads of orbs, which are even too remote for the reach of telescopic
vision.

An illustrative experiment must close our consideration of relative
operations of rotation and gravitation. We well know that a body in
a fluid state would, if suspended above the earth, it being at the
same time free to take any form, naturally assume that of a flattened
spheroid, from the action of the mass of the earth upon it: whereas the
force of cohesive attraction acting equally from all sides of a centre,
would, if uninfluenced, necessarily produce a perfect sphere. The best
method of showing that this would be the case, is as follows:--

Alcohol and water are to be mixed together until the fluid is of the
same specific gravity as olive oil. If, when this is effected, we
drop globules of the oil into the mixed fluid, it will be seen that
they take an orbicular form;--and, of course, in this experiment the
power of the earth’s gravitating influence is neutralized. The same
drops of oil under any other conditions would be flattened. Simple as
this illustration is, it tells much of the wondrous secret of those
beautifully balanced forces of cohesion and of gravitation; and from
the prosaic fact we rise to a great philosophical truth. Our experiment
may lead us yet farther in exemplification of known phenomena. If we
pass a steel wire through one of those floating spheres of oil, and
make it revolve rapidly and steadily, thus imitating the motion of a
planet on its axis, the oil spreads out, and we have the spheroidal
form of our earth. Increase the rapidity of this rotation, and when a
certain rate is obtained the oil widens into a disc, a ring separates
itself from a central globe, and at a distance from it still revolves
around it.[24] Here we have a miniature representation of the ring
of Saturn. This is a suggestive experiment, the repetition of which,
by reflective minds, cannot fail to lead to important deductions. The
phenomena of cohesion, of motion, and gravitation, are all involved;
and we produce results resembling, in a striking manner, the conditions
which prevail in the planetary spaces, under the influence of the same
powers. If we take a glass globe, and having filled it with a fluid of
the proper density, drop into it large and small globules of oil, we
may produce an instructive representation of the stellar vault, with
its beautiful spheres of light revolving in their respective orbits;
and though crossing each other’s paths, still moving in obedience to
attracting and repelling forces--onward in perfect harmony.

From the centre of our earth to the utmost extremity of the
universe--from the infinitely small to the immensely vast--gravitation
exerts its force. It is met on all sides by physical powers acting in
antagonism to it, but, like a ruling spirit, it restrains them in their
wildest moods.

    The smallest dust which floats upon the wind
    Bears this strong impress of the Eternal Mind.
    In mystery round it, subtile forces roll;
    And gravitation binds and guides the whole.
    In every sand, before the tempest hurl’d,
    Lie locked the powers which regulate a world,
    And from each atom human thought may rise
    With might to pierce the mysteries of the skies,--
    To try each force which rules the mighty plan,
    Of moving planets, or of breathing man;
    And from the secret wonders of each sod,
    Evoke the truths, and learn the power of God.


FOOTNOTES:

[13] Three hypotheses may be used to account for this most curious
phenomenon.

1st. The body shines by its own light, and then explodes like a
sky-rocket, breaking into minute fragments too small to be any longer
visible to the naked eye.

2nd. Such a body, having shone by its own light, suddenly ceases to
be luminous. “The falling stars and other fiery meteors which are
frequently seen at a considerable height in the atmosphere, and which
have received different names according to the variety of their figure
and size, arise from the fermentation of the effluvia of acid and
alkaline bodies which float in the atmosphere. When the more subtile
parts of the effluvia are burned away, the viscous and earthy parts
become too heavy for the air to support, and by their gravity fall to
the earth.”--Keith’s _Use of the Globes_. According to Sir Humphry
Davy, in the Philosophical Transactions for 1847, “the luminous
appearances of shooting stars and meteors cannot be owing to any
inflammation of elastic fluids, but must depend upon the ignition of
solid bodies.”

3. The body shines by the reflected light of the sun, and ceases to be
visible by its passing into the earth’s shadow, or, in other words,
is eclipsed. Upon the two former suppositions the fact of the star’s
disappearance conveys to us no knowledge of its position, or of its
distance from the earth; and all that can be said is, that if it be
a satellite of the earth, the great rapidity of its motion involves
the necessity of its being at no great distance from the earth’s
surface--much nearer than the moon; while the resistance it would
encounter in traversing the air would be so great that it is probably
without the limits of our atmosphere. _Sir J. W. Lubbock leans to the
third hypothesis._--Sir J. W. Lubbock, _On Shooting Stars_: Phil. Mag.
No. 213, p. 81.

Sir J. Lubbock also published a supplementary paper on the same
subject, in No. 214, p. 170.

Mr. J. P. Joule entertains an hypothesis with respect to Shooting
Stars similar to that advocated by Chladni to account for meteoric
stones, and he reckons the ignition of these miniature planetary bodies
by their violent collision with our atmosphere, to be a remarkable
illustration of the doctrine of the equivalency of heat to mechanical
power, or _vis viva_.

If we suppose a meteoric stone of the size of a six-inch cube to enter
our atmosphere at the rate of eighteen miles per second of time, the
atmosphere being 1/100 of its density at the earth’s surface, the
resistance offered to the motion of the stone will in this case be at
least 51,600 lbs.; and if the stone traverse twenty miles with this
amount of resistance, sufficient heat will thereby be developed to give
1° Fahrenheit to 6,967,980 lbs. of water. Of course by far the largest
portion of this heat will be given to the displaced air, every particle
of which will sustain the shock, whilst only the surface of the stone
will be in violent collision with the atmosphere. Hence the stone may
be considered as placed in a blast of intensely heated air, the heat
being communicated from the surface to the centre by conduction. Only
a small portion of the heat evolved will therefore be received by the
stone; but if we estimate it at only 1/100 it will still be equal
to 1° Fahrenheit per 69,679 lbs. of water, a quantity quite equal
to the melting and dissipation of any materials of which it may be
composed.--Mr. J. P. Joule, _On Shooting Stars_: Phil. Mag. No. 216, p.
348.

[14] “Laplace conjectures that in the original condition of the solar
system, the sun revolved upon his axis, surrounded by an atmosphere
which, in virtue of an excessive heat, extended far beyond the orbits
of all the planets, the planets as yet having no existence. The heat
gradually diminished, and as the solar atmosphere contracted by
cooling, the rapidity of its rotation increased by the laws of rotatory
motion; and an exterior zone of vapour was detached from the rest,
the central attraction being no longer able to overcome the increased
centrifugal force. This zone of vapour might in some cases retain
its form, as we see it in Saturn’s ring; but more usually the ring
of vapour would break into several masses, and these would generally
coalesce into one mass, which would revolve about the sun,”--Whewell’s
_Bridgewater Treatise_.

The following passage is translated by the same author from Laplace:--

“The anterior state (a state of cloudy brightness) was itself preceded
by other states, in which the nebulous matter was more and more
diffuse, the nucleus being less and less luminous. We arrive in this
manner at a nebulosity so diffuse, that its existence could scarce be
suspected. Such is in fact the first state of the nebula which Herschel
carefully observed by means of his telescope.”

Sir William Herschel has the following observations on these remarkable
masses:--

“The nature of planetary nebulæ, which has hitherto been involved in
much darkness, may now be explained with some degree of satisfaction,
since the uniform and very considerable brightness of their apparent
disc accords remarkably well with a much condensed, luminous fluid;
whereas, to suppose them to consist of clustering stars will not so
completely account for the milkiness or soft tint of their light, to
produce which it would be required that the condensation of the stars
should be carried to an almost inconceivable degree of accumulation.

“How far the light that is perpetually emitted from millions of suns
may be concerned in this shining fluid, it might be presumptuous to
attempt to determine; but notwithstanding the inconceivable subtilty
of the particles of light, when the number of the emitting bodies
is almost infinitely great, and the time of the continual emission
indefinitely long, the quantity of emitted particles may well become
adequate to the constitution of a shining fluid or luminous matter,
provided a cause can be found that may retain them from _flying off,
or reunite them_.”--_Observations on Nebulous Stars_: Philosophical
Transactions, vol. lxxxi. A.D. 1791.

In addition, the following Memoirs on the same subject, by Sir
William Herschel, have been published in the Philosophical
Transactions:--_Catalogue of 1000 Nebulæ and Clusters of Stars_, vol.
lxxvi.; _Catalogue of another 1000, with remarks on the Heavens_, vol.
lxxix.; _Catalogue of 500 more, with remarks as above_, vol. xcii.;
_Of such as have a cometary appearance_, vol. ci.; _Of planetary
nebulæ_, ibid.; _Of stellar nebulæ_, ibid.; _On the sidereal part of
the heavens, and its connection with the nebulous_, vol. civ.; _On the
relative distances of clusters of nebulous stars_, vol. cviii.

[15] Lord Rosse’s beautiful telescopes have been formed upon principles
which appear to embrace the best possible conditions for obtaining
a reflecting surface which should reflect the greatest quantity of
light, and retain that property little diminished for a length of
time. The alloy used for this purpose consists of tin and copper in
atomic proportions, namely, one atom of tin to four atoms of copper,
or by weight 58·9 to 126·4.--_On the Construction of large Reflecting
Telescopes_: by Lord Rosse. Report of the Fourteenth Meeting of the
British Association, 1844, p. 79.

[16] The best description of the Zodiacal Light occurs in a letter
furnished by Sir John Herschel to the _Times_ newspaper in March,
1843:--“The zodiacal light, as its name imports, invariably appears
in the zodiac, or, to speak more precisely, in the plane of the sun’s
equator, which is 7° inclined to the zodiac, and which plane, seen from
the sun, intersects the ecliptic in longitude 78° and 258°, or so much
in advance of the equinoctial points: in consequence it is seen to the
best advantage at, or a little after, the equinoxes; after sunset,
at the spring, and before sunrise, at the autumnal equinox; not only
because the direction of its apparent axis lies at those times more
nearly perpendicular to the horizon, but also because at those epochs
we are approaching the situation when it is seen most completely in
section.

“At the vernal equinox the appearance of the zodiacal light is that
of a pretty broad pyramidal, or rather lenticular, body of light,
which begins to be visible as soon as the twilight decays. It is very
bright at its lower or broader part near the horizon, and, if there
be broken clouds about, often appears like the glow of a distant
conflagration, or of the rising moon, only less red, giving rise, in
short, to amorphous masses of light such as have been noticed by one of
your correspondents as possibly appertaining to the comet. At higher
altitudes, its light fades gradually, and is seldom traceable much
beyond the Pleiades, which it usually, however, attains and involves,
and (what is most to my present purpose) its axis at the vernal equinox
is always inclined (to the northward of the equator) at an angle of
between 60° and 70° to the horizon, and it is most luminous at its
base, resting on the horizon, where also it is broadest, occupying,
in fact, an angular breadth of somewhere about 10° or 12° in ordinary
clear weather.”

[17] “The assumption that the extent of the starry firmament is
literally infinite has been made by one of the greatest of astronomers,
the late Dr. Olbers, the basis of a conclusion that the celestial
spaces are, in some slight degree, deficient in _transparency_; so that
all beyond a certain distance is, and must remain for ever, unseen; the
geometrical progression of the extinction of light far outrunning the
effect of any conceivable increase in the power of our telescopes. Were
it not so, it is argued, every part of the celestial concave ought to
shine with the brightness of the solar disc, since no visual ray could
be so directed as not, in some point or other of its infinite length,
to encounter such a disc.”--_Edinburgh Review_, p. 185, for January,
1848; _Etudes d’Astronomie Stellaire_.

[18] In the _Astronomische Nachrichten_ of July, 1846, appeared a
Memoir by M. Mädler, _Die Centralsonne_. The conclusions arrived at by
Mädler may be understood from the following quotation from a French
translation, made by M. A. Gautier, in the _Archives des Sciences
Physiques et Naturelles_, for October, 1846:--“Quoiqu’il résulte
de ce qui précède que la région du ciel que j’ai adoptée satisfait
à toutes les conditions posées plus haut, il n’en est pas moins
convenable de la soumettre à toutes les épreuves possibles. Plusieurs
essais de combinaisons différentes m’ont convaincu qu’on ne pourrait
trouver aucun autre point dans le ciel qui pût tenir lieu, même d’une
manière approchée, que celui que j’ai adopté. On pourrait maintenant
m’addresser l’objection que, si la région du ciel où se trouve le
centre de gravité de notre système d’étoiles fixes, est déterminée
par ce qui précède entre certaines limites, il n’en résulte pas la
nécessité de choisir Alcyone pour ce centre, attendu qu’il pourrait
bien tomber sur quelqu’autre étoile située dans le groupe ou dans son
voisinage. Mais outre que c’est tout près de là que se trouve le groupe
le plus brillant et le plus riche en étoiles de tout le ciel, et qu’il
ne s’agit point ici d’un point arbitraire situé dans le voisinage
peu apparent et qui n’ait rien qui le distingue, il ne se trouve nul
part, même dans la région voisine, une aussi exacte concordance des
mouvements propres qu’ici, et ces mouvements correspondent mieux que
tous les autres aux conditions établies plus haut. Or si l’on doit
considérer ce groupe central, entre les étoiles également éloignées, on
peut présumer que la plus brillante de beaucoup présente la plus grande
masse. Outre cela Alcyone, considérée optiquement, est au milieu du
groupe des Pleïades; et son mouvement propre, déterminé par Bessel, est
plus exactement en accord avec la moyenne de ceux des autres Pleïades;
ainsi que des étoiles de cette région jusqu’à 10° de distance. _Je puis
donc établir comme conséquence de tout ce qui précède, que le groupe
des Pleïades est le groupe central de l’ensemble du système des étoiles
fixes, jusqu’aux limites extérieures déterminées par la Voie Lactée;
et que Alcyone est l’étoile de ce groupe qui paraît être, le plus
vraisemblablement, le vrai Soleil central._”

[19] See the article _On Gravitation_, Penny Cyclopædia, from the pen
of the Astronomer-Royal.

[20] Delambre dates the commencement of modern astronomical observation
in its most perfect form from Maskelyne, who was the first who gave
what is now called a standard catalogue (A.D. 1790) of stars; that
is, a number of stars observed with such frequency and accuracy, that
their places serve as standard points of the heavens. His suggestion
of the _Nautical Almanack_, and his superintendence of it to the end
of his life, from its first publication in 1767, are mentioned in the
_Almanack_ (vol. i. p. 364); his _Schehallion Experiment on Attraction_
in vol. iii. p. 69; and the character of his _Greenwich Observations in
Greenwich Observatory_ in vol. ii. p. 442.

[21] _Experiments to determine the Density of the Earth._ By Henry
Cavendish, Esq., F.R.S. and F.A.S.--Philosophical Transactions, 1798.

[22] Adams: _An Explanation of the observed irregularities in the
motion of Uranus, on the hypothesis of disturbance caused by a more
distant Planet_.--Appendix to Nautical Almanack for 1851.

[23] Le Verrier: _Premier Mémoire sur la théorie d’Uranus_, Comptes
Rendus, vol. xxi.; _Sur la planête qui produit les anomalies observées
dans le mouvement d’Uranus_.--_Ib._ vol. xxiii.

[24] The experiment alluded to is one of a series by M. Plateau, who
thus describes his arrangement of the fluid:--“We begin by making a
mixture of alcohol and distilled water, containing a certain excess
of alcohol, so that when submitted to the trial of the test tube
it lets the small sphere of oil fall to the bottom rather rapidly.
When this point is obtained, the whole is thrown upon filters, care
being taken to cover the funnels containing these last with plates
of glass; this precaution is taken in order to prevent, as much as
possible, the evaporation of the alcohol. The alcoholic liquor passes
the first through the filters, ordinarily carrying with it a certain
number of very minute spherules of oil When the greater part has thus
passed, the spherules become more numerous; what still remains in the
first filters, namely, the oil and a residue of alcoholic liquor, is
then thrown into a single filter placed on a new flask. This last
filtration takes place much more slowly than the first, on account of
the viscosity of the oil; it is considerably accelerated by renewing
the filter once or twice during the operation. If the funnel has been
covered with sufficient care, the oil will collect into a single mass
at the bottom of the flask under a layer of alcoholic liquor.”--_On the
Phenomena presented by a free Liquid Mass withdrawn from the action of
Gravity._ By Professor Plateau, of the University of Ghent. Translated
from the _Memoirs of the Royal Academy of Brussels_, vol. xvi.; in the
_Scientific Memoirs_, vol. iv. part 13.




CHAPTER IV.

MOLECULAR FORCES.

  Conditions of Matter--Variety of organized
    Forms--Inorganic Forms--All matter reducible to the
    most simple conditions--Transmutation, a natural
    operation--Chemical Elementary Principles--Divisibility of
    Matter--Atoms--Molecules--Particles--Molecular Force includes
    several Agencies--Instanced in the Action of Heat on Bodies--All
    Bodies porous--Solution--Mixture--Combination--Centres of
    Force--Different States of Matter (Allotropic Conditions)--Theories
    of Franklin, Æpinus, and Coulomb--Electrical and Magnetic
    Agencies--Ancient Notions--Cohesive Attraction, &c.


In contemplating the works of nature, we cannot but regard, with
feelings of religious admiration, the infinite variety of forms under
which matter is presented to our senses. On every hand the utmost
diversity is exhibited; through all things we trace the most perfect
order; and over all is diffused the charm of beauty. It is the
uneducated or depraved alone who find deformities in the creations by
which we are surrounded.

The three conditions of matter are--the solid, the fluid, and the
aëriform; and these belong equally to the organic and the inorganic
world.

In organic nature we have an almost infinite variety of animal form,
presenting developments widely different from each other, yet in every
case suited to the circumstances required by the position which the
creature, occupies in the scale of being. Through the entire series,
from the Polype to the higher order of animals, even to man, we find a
uniformity in the progress towards perfection, and a continuity in the
series, which betrays the great secret, that the mystery of life is
the same in all,--a pervading spiritual essence associated with matter,
and modifying it by the master-mechanism of an Infinite mind.

In the vegetable clothing of the surface of the earth, which fits it
for the abode of man and animals--from the confervæ of a stagnant pool,
or the lichen of the wind-beaten rocks, to the lordly oak or towering
palm--a singularly beautiful chain of being presents itself to the
contemplative mind, and we cannot but trace the gradual elevation in
the scale of organization.

In the inorganic world, where the great phenomena of life are wanting,
we have constantly exhibited the working of powers of a strangely
complicated kind. The symmetrical arrangement of crystals--the
diversified characters of mineral formations--the systematic
aggregations of particles to form masses possessing properties of a
peculiar and striking nature--all prove, that agencies, which science,
with all its refinements, has not yet detected, are unceasingly at
work. Heat, electricity, chemical power--whatever that may be--and
the forces of cohesion, are known to be involved in the production of
the forms we see; but contemplation soon leads to the conviction that
these powers are subordinate to others which we know not of. We know
only the things belonging to the surface of our planet, and these but
superficially. The geologist traces rock-formations succeeding each
other (from the primary strata holding no traces of organized forms,
through the Paleozoic series, in which, step by step, the history of
animal life is recorded,) to the more recent formations, teeming with
relics, which, though allied to some animal types still existing, are
generally such as have passed away. The naturalist searches the earth,
the waters, and the air, for their living things; and the diversity
of form, the variety of condition, and the perfection of organization
which he discovers as belonging to this our epoch--differing from,
indeed bearing but a slight relation to, those which mark the earth’s
mutations--exhibit, in a most striking view, the endless variety of
characters which matter can assume.

We are so accustomed to all these phenomena of matter, that it is with
some difficulty we can bend ourselves to the study of the more simple
conditions in which it exists.

The solid crusts of this telluric sphere--the waters and the
atmosphere--the diversified fabrics of the vegetable kingdom--and the
still more complicated structures of men and animals--are, altogether,
but the aggregation of minute particles in accordance with certain
fixed laws. By mechanical means all kinds of matter may be reduced to
powder, the fine particles of which would not appear very different
from each other, but each atom has been impressed with properties
peculiar to itself, which man has no power to change.

To nature alone belongs the mysterious property of transmutation. The
enthusiastic alchemist, by the agency of physical forces, dissipates a
metal in vapour; but it remains a metal, and the same metal still. By
the Hermetic art he breaks up the combination of masses; but he cannot
alter the principles of any one of the elements which form the mass
upon which his skill is tried.

Every atom is invested with properties peculiar to all of its class;
and each one possesses powers, to which in mute obedience it is
compelled, by which these properties are modified, and the character of
matter varied. What are those properties? Do we know anything of those
powers?

The earth, so far as we are acquainted with it, is composed of about
sixty principles, which we call elementary. These are the most simple
states to which we can reduce matter, and from them all the forms of
creation yet examined by the chemist are produced. These elementary
principles are, some of them, permanently gaseous under the ordinary
temperature, and others exist as solid masses; the difference between
the two conditions being regulated, as it appears, by the opposing
forces of heat and cohesive attraction.

Matter has been regarded by some as infinitely divisible; but the known
conditions of chemical combinations lead to the conclusion that there
are limits beyond which matter cannot be divided.[25] The theory of
atoms having determinate characters, and possessing symmetric forms,
certainly has the advantage of presenting to the human mind a starting
point--a sort of standing ground,--from which it can direct the survey
of cosmical phenomena. The metaphysical hypothesis, which resolves all
matter into properties, and refers all things to ideas, leaves the
mind in a state of uncertainty and bewilderment.

Adapting the views of Dumas, with some modifications,[26] it will be
found more satisfactory to regard the _ultimate atoms_ of matter as
points beyond the reach of our examination; which, according to a law,
determined by the influences of the so-called imponderable forces,
unite to form _molecules_. Again, these molecules combine to form the
_particles_ of the mass which we may regard as the limit of mechanical
division. The particles of solid bodies are solid, those of fluids
fluid, and those of gaseous bodies are themselves aëriform; but it does
not follow that the molecules of any body should be necessarily solid,
fluid, or aëriform, from the circumstance of their having formed the
particles of a body in one of these states.

As this planet--a molecule in space--is formed of aggregated atoms, and
enveloped by its own physical agencies--and as it is involved in the
infinitely extending influences of other planetary molecules, and thus
forms part of a system--so the molecules of any mass are grouped into a
system or particle, which possesses the great characteristic features
of the whole.

In an aëriform body the particles are in a state of extreme tenuity,
the molecules being themselves, by the influence of some repulsive
force, just on the verge where cohesion exerts its decaying power. In
fluid bodies the attenuation of the particles is less--the particles
and also the molecules are nearer together,--whereas, in the solid
body, the forces of cohesion are most strongly exerted, and all the
molecular conditions brought more powerfully into action.

Under the term molecular force, we include several agencies,--not
alike in the phenomena which they exhibit, but which are all-powerful
in producing the general characteristics of bodies. These require a
somewhat close examination. All the particles of even a solid mass may
be brought under conditions on which they are free to move. By heat we
can increase the length and thickness of a bar of iron, or any other
metal, and at length produce the fluid state,--a melted metal flows as
freely as water in a stream. Fluids, and gases in like manner obey the
dispersive influence of caloric. From these and other analogous results
we learn that all bodies have a greater or less degree of porosity.
The distance at which the particles of fluid bodies are maintained is
strikingly proved by the fact, that hydrated salts dissolved in water
occupy no more space than that which is equal to the water contained
in the crystalline body; while anhydrous salts dissolve without at
all increasing the bulk of the fluid. All the solid matter of the salt
must, in these cases, it would appear, go to fill up the interstitial
spaces which we suppose to exist in the liquid.[27]

The conditions which regulate the solubility of bodies, and the power
of solution, regarded either as a mechanical or a chemical process, are
very obscure. We might be led to suppose, that those bodies possessing
the largest amount of unoccupied space were capable of holding the
greatest quantity of soluble matter dissolved. This, however, is far
from being the case, the denser fluids generally having the greatest
solvent power.

The peculiar manner in which hydrogen gas appears to dissolve solid
substances,--as iron, potassium, sodium, sulphur, phosphorus,
selenium, and arsenic, may be explained by regarding the results as
a manifestation of the powers of chemical affinity over the forms of
bodies. In like manner, the solution of salt in water, or the mixture
of alcohol in that fluid, may be viewed as chemical phenomena, although
usually considered as simple cases of solution or mixture: alterations
of temperature and other physical changes taking place in either. If
two masses of metal,--either tin and copper, for example,--are melted
and combined, the united mass will not equal the bulk of the two
masses. If a pint measure of oil of vitriol and an equal quantity of
water are mixed together, the combined fluids will not fill a two pint
measure.[28]

In these instances a large quantity of heat is rendered sensible, as
if it had been squeezed out by the force with which the particles
combined, from interstices, which were filled with, what we may be
allowed to call, an atmosphere of heat. Hence we conclude that, amongst
the influences determining the molecular constitution of a body, heat
performs an important part. All these facts go to prove that the atoms
which form the compound body, whatever may be its character, are
disposed of as so many centres of force, which act by influences of a
peculiar character upon each other. That these influences are dependent
upon known physical forces is certain; but the laws by which the powers
of the ultimate atom are altered remain still unknown.

In the great operations of nature, changes are produced which we cannot
understand, and variations of condition do certainly occur, which may
be regarded as instances of transmutation.

Amongst others, we may adduce the different states in which we
know carbon to exist. We have the diamond with its beautiful
light-refracting property, its hardness and high specific gravity,
capable of being converted into graphite and coke.[29] Charcoal,
graphite, and the diamond, are totally unlike each other, yet we know
they are each composed of the same atoms. Charcoal is a black irregular
substance, light, and readily inflammable; graphite is crystallizable;
but the forms of its crystals cannot be referred to those of the
diamond, and it burns with difficulty. The diamond occurs in the most
regular and beautifully transparent forms; and it can be burned only
at the highest artificial temperatures. We are, however, convinced by
experiment that the brilliant and transparent gem is made up of the
same atoms as those which go to form the dull black mass of charcoal.
From diamonds, as is above stated, coke has been formed by the heat
of the voltaic battery, and recent experiments have proved that the
volatilized carbon constantly passing off from one of the poles of a
sufficiently powerful battery, is deposited in a crystalline powder,
possessing most of the properties, as it regards hardness, &c. of true
diamond dust. What is the mystery of this? We know not. The peculiar
conditions have been the subjects of anxious study; but science has not
yet let in a ray of light upon the mystery. That a different state--it
has been called an _allotropic_ condition--is often induced in the
same class of atoms is certain; and hence the variety of the resulting
compounds. To continue our illustrations with carbon--may not its
combinations, in uniform proportions with oxygen and hydrogen,[30] owe
their differences to some allotropic change in the ultimate atoms of
this element.

We know that silicon--the metallic base of flint--is capable of
assuming two or more different states; and that sulphur, selenium,
phosphorus, and arsenic, are susceptible of these remarkable changes
in which, without the slightest variation in the chemical character, a
complete change in the physical condition is produced. Copper, iron,
tin, and manganese, are known to exist in at least two states of
physical dissimilarity, and many of the rarer metals exhibit the same
peculiarity.[31] Hence, may we not infer that some of those substances,
which we now term elementary, are but altered conditions of the same
element? The resemblance between many of those bodies strengthens
the supposition. Iridium and platinum,--iron and nickel,--chlorine,
bromine, iodine, and probably fluorine,--are good examples of these
similarities, although these bodies are all distinguished by physical
and chemical differences.

The light-refracting gem, which glistens on the neck of beauty, and is
valued for its transparency, differs only from the rude lump of coke in
its molecular arrangement. Chemistry teaches us that we may, without
producing any disarrangement of the affinities, but by merely setting
up molecular disturbance, effect decided changes, as is strikingly
shown in the colour of iodide of mercury changing from red to yellow
under slight influences of heat, and back again to red by a gentle
mechanical disturbance. By a slight change, merely molecular, iron may
be made to resemble platinum in its physical properties.[32] An iron
wire plunged into nitric acid is attacked by the acid with violence;
but if one extremity of the wire is heated in the flame of a spirit
lamp, such a change of state is produced throughout the entire length
of the wire, that if it be now plunged into nitric acid no effect is
produced upon it. On studying this question, we find good reason for
supposing that bodies which, though physically different, resemble
each other in some of their properties, iodine, bromine, &c., are the
results of different _allotropic_ conditions which have been impressed
upon the ultimate atoms, similar to those observed in the substances
named. This hypothesis appears to be more in accordance with the great
principles which we must conceive guided the labours of an Infinite
Mind, than that which supposes a vast number of individual creations.
It will be seen in the sequel that light, heat, electricity, and
chemical action, have the power of producing yet more striking changes
in the forms of bodies. Is it not probable that, according to the
operations of these agents, either combined or separate, acting over
different spaces of time, and under varying circumstances, in relation
to the molecular forces, all those _allotropic_ states may be produced?
Hence bodies may be discovered, which,--from the imperfections of
science,--resisting our means of analysis, must, for a time, be
regarded as new elements, whereas they are possibly only altered states
of the same substance.

The experiments of Faraday and of Plücker prove that all matter exists
in certain polar conditions, having powers of mutual attraction
and repulsion.[33] Are the molecular forces, so called, to be
referred to any of those powers which are involved in the general
term magnetic-polarity? Are they not probably the result of some
ultimate principle of which these properties are but the modified
manifestations? These questions will now be generally answered in
favour of magnetism; but in our ignorance we should pause; the next
generation will without doubt find another solution for the problem.

Franklin supposed the ultimate atoms of bodies to be surrounded by
a subtile fluid or ether, which they have the power of condensing
upon their surfaces with great force--and we have experiments showing
that this is probable[34]--whilst he regarded the atoms of the ether
itself as mutually repellent, thus establishing an equilibrium of
forces. Æpinus reduced the hypothesis of Franklin to a mathematical
theory; and Coulomb _proved_ that the force with which the repulsion
of the ethereal atoms and the attraction of the material molecules
are produced, is, like universal attraction,--to whatever power that
may be due,--regulated by the law of the inverse ratio of the square
of the distance. These views are found, upon minute examination, to
hold true to the phenomena with which inductive science has made us
acquainted; and the striking manner in which, when submitted to the
rigorous investigations of geometers, they agree with known conditions
of electricity, appears certainly to favour the opinion that this power
may be materially connected with these molecular arrangements.

Many of the phenomena which are connected with the magnetic influences
also bear in a remarkable manner upon this inquiry. But, without
the necessary proof of direct experimental evidence, it were as
unphilosophical to refer the binding together of the molecules of
matter to the agency of electricity, as it would be to adopt the theory
of the hooked atoms of Epicurus, or the astrological dream of the
sympathies of matter.[35]

Science, however, enables us to infer with safety that the mechanical
powers which regulate the constitution of a cube of marble, or a
granite mountain, are of a similar order to those which determine the
earth’s relation to the other planets in the solar system, and that
solar system itself a unit, in the immensity of space, to the myriads
of suns which spangle the stellar vault.

In fine, cohesion, or the attraction of aggregation, is a power
employed in binding particle to particle. To cohesion, we find we have
heat opposed as a repellent force; and the mysterious operations of
those electrical phenomena, generally referred to as polar forces, are
constantly, it is certain, interfering with its powers. In addition,
we have seen that in nature there exists an agency which is capable
of changing the constitution of the ultimate atoms, and of thus
giving variety to each resulting mass. What this power may be, our
science cannot tell; but our reason leads us, with firm conviction,
to the belief that it is a principle which is, beyond all others in
its subtile influences which equally universal with, appears to rise
superior to gravitation; and which, like a spirituality, shadows forth
to our dwarf conceptions the immensity of the divine power of the
omniscient Creator.

The molecular forces involve a consideration of all the known physical
powers, the study of which, in their operations on matter, will engage
our attention. But it is pleasant to learn, as we advance step by step
in our examination of the phenomena of creation, that we may study
the grand in what externally appears the simple, and learn, in the
mysteries of a particle, the high truths which science has to tell of a
planet.

It may appear that the forces of gravitation and cohesion are regarded
as identical. Many phenomena, which we are enabled to reach by the
refinements of inductive inquiry, certainly present to us a striking
similarity in the laws which regulate the operations of these powers;
but it must be remembered that their identity is not established. So
far from this, we know the law of gravitating force. Newton determined
with surprising accuracy, that the action of this power diminishes with
the distance as the universe square, but cohesive force is exerted only
at such distances that it is impossible to determine whether or not it
is subjected to the same law. To quote the words of Young: “The whole
of our inquiries respecting the intimate nature of forces of any kind
must be considered merely as speculative amusements, which are of no
further utility than as they make our views more general, and assist
our experimental investigations.”[36]


FOOTNOTES:

[25] “The divisibility of matter is great beyond the power of
imagination, but we have no reason for asserting that it is infinite;
for the demonstrations which have sometimes been adduced in favour
of this opinion are obviously applicable to space only. The infinite
divisibility of space seems to be essential to the conception that we
have of its nature, and it may be strictly demonstrated that it is
mathematically possible to draw an infinite number of circles between
any given circle and its tangent, none of which shall touch either of
them except at the general point of contact; and that a ship following
always the same oblique course with respect to the meridian,--for
example, sailing north-eastwards,--would continue perpetually to
approach the pole without ever completely reaching it. But when we
inquire into the truth of the old maxim of the schools, that all
matter is infinitely divisible, we are by no means able to decide so
positively. Newton observes that it is doubtful whether any human means
may be sufficient to separate the particles of matter beyond a certain
limit; and it is not impossible that there may be some constitution
of atoms, or single corpuscles, on which their properties, as matter,
depend, and which would be destroyed if the units were further divided;
but it appears to be more probable that there are no such atoms, and
even if there are, it is almost certain that matter is never thus
annihilated in the common course of matter.”--_The Essential Properties
of Matter_: Young’s _Natural Philosophy_; ed. by Rev. P. Kelland.

[26] “Two very different hypotheses have been formed to explain the
nature of matter, or the mode of its formation; the one known as
the _atomic_ theory, the other, the _dynamic_. The founder of the
former and earlier was Leucippus: he considered the basis of all
bodies to be extremely fine particles, differing in form and nature,
which he supposed to be dispersed through space, and to which his
follower Epicurus first gave the name of atoms. To these atoms he
attributed a rectilinear motion, in consequence of which such as
are homogeneous united, whilst the lighter were dispersed through
space. The author of the second hypothesis was the famous Kant. He
imagined all matter existed, or was originated, by two antagonist and
mutually counteracting principles, which he called attraction and
repulsion, all the predicates of which he referred to motion. Most
modern philosophers, and foremost amongst them Ampère and Poisson, have
adopted an hypothesis combining the features of both the preceding.
They regarded the atoms as data, deriving their origin from the Deity
as the first cause, and consider their innate attractive and repulsive
force as a necessary condition to their combination in bodies. The
main features of this hypothesis are borrowed from Aristotle, inasmuch
as he supposed the basis of all bodies to be the four elements known
to the ancients, the particles of which, endued with certain powers,
constituted bodies. According to Ampère, all bodies consist of equal
particles, and they again of molecules that, up to a certain distance,
attract each other. Their distance from each other he supposed to be
regulated by the intensity of the attractive and repulsive forces,
the latter of which preponderates.”--Peschel’s _Elements of Physics_;
translated by E. West, 1845.

[27] This was first proved by the researches of Dr. Dalton: the subject
will be again alluded to under the consideration of atomic volumes.

[28] These peculiar phenomena may be studied advantageously in the
works of most of the eminent European chemists. In our own language the
reader is referred to Dr. Thompson’s _Outline of the Sciences of Heat
and Electricity_, 2nd edition; Brande’s _Manual of Chemistry_--Art.
_Specific Heat_; Graham’s _Elements of Chemistry_; and Daniell’s
_Introduction to the Study of Chemical Philosophy_.

[29] The conversion of the diamond into graphite and coke was first
effected by the agency of the galvanic arc of flame, by M. Jaquelini,
and communicated to the Academy of Sciences in 1847, in a Memoir
entitled, _De l’action calorifique de la pile de Bunsen, du chalumeau à
gaz oxygène et hydrogène sur le carbon pur, artificiel et naturel_. See
_Comptes Rendus_, 1847, vol. xxiv. p. 1050; also _Report of the British
Association_, for 1847, (_Transactions of Sections_) p. 50.

[30] “In the annual report on the progress of chemistry, presented
to the Royal Academy of Stockholm, in March 1840, I have proposed to
designate by the term _allotropic state_, that dissimilar condition
which is observed in certain elements, and long known examples of which
are found in the different forms of carbon, as graphite and diamond.

“Although these dissimilar conditions, which I have here called
allotropic, have long since attracted attention in one or two elements,
still they have been regarded as exceptions to the general rule. It
is at present my object to show that they are not so rare; that it
is probably rather a general property of the elements to appear in
different allotropic conditions; and that although we have hitherto
been unable to obtain several of the elements when uncombined in
their allotropic states, still their compounds indicate the same with
tolerable distinctness.”--_Berzelius on the Allotropy of the Elementary
Bodies_, _&c._: Poggendorff’s Annalen, 1844. Scientific Memoirs, vol.
iv. p. 240.

[31] “Copper, when reduced by hydrogen at a heat below that of
redness, on exposure to air soon becomes converted throughout its
mass into protoxide; and when it is triturated for some time with
an equivalent quantity of sulphur, it combines with it according to
Böttcher’s experiments, producing flame, and forming sulphuret of
copper. If, however, the copper be reduced by hydrogen at a red heat,
still considerably below the temperature at which it softens and
begins to melt, it remains for years unchanged by exposure to air,
and cannot be made to combine with sulphur without the application of
heat. Iron, cobalt, and nickel, when reduced by hydrogen below a red
heat, inflame after they have cooled, if exposed to the air; and if
they are immediately placed in water to avoid their taking fire, they
inflame when they are again removed, and have become nearly dry. If we
compare this behaviour with that of iron reduced by heat, and with iron
in that state in which it forms the conductor of a galvanic current
without becoming oxidized, it would appear that these peculiarities
depended upon something more than a difference of mechanical
condition.”--_Berzelius on the Allotropy of Elementary Bodies._ See
_On the Isomeric Conditions of the Peroxide of Tin_: by Prof. H.
Rose.--Chemical Gazette, Oct. 1848.

[32] On this curious subject, and its history, see Bergman’s _Dissert.
de Phlog. quantitate in Metallis_, 1764. Kirwan, _On the Attractive
Powers of Mineral Acids_: Philosophical Transactions. Kier’s
_Experiments and Observations on the Dissolution of Metals in Acids_:
Phil. Trans. 1790.

From these valuable papers it will be seen that the peculiar states
of iron had already attracted attention, particularly those “inactive
conditions” noticed in a “_Note sur la Manière d’agir de l’Acide
nitrique sur le Fer, par J. F. W. Herschel_,” Aug. 1833; and previously
indicated by M. H. Braconnot, _Sur quelques Propriétés de l’Acide
nitrique_, Annales de Chimie, vol. lii. p. 54. Reference should also be
made to the Memoirs of Sir John Herschel, _On the Action of the Rays
of the Solar Spectrum on Vegetable Colours_, _&c._: Phil. Trans. vol.
cxxxiii. p. 221; and _On the Separation of Iron from other Metals_:
Phil. Trans. vol. cxi. p. 293; and several papers by Schönbein, in the
Philosophical Magazine, from 1837.

[33] Faraday, in his memoir _On new Magnetic Actions, and on the
Magnetic Conditions of all Matter_, says:--“By the exertion of this new
condition of force, the body moved may pass either along the magnetic
lines or across them, and it may move along or across them in either
or any direction, so that two portions of matter, simultaneously
subject to this power, may be made to approach each other as if they
were mutually attracted, or recede as if mutually repelled. All the
phenomena resolve themselves into this, that a portion of such matter,
when under magnetic action, tends to move from stronger to weaker
places or points of force. When the substance is surrounded by lines
of magnetic force of equal power on all sides, it does not tend to
move, and is then in marked contradistinction with a linear current of
electricity under the same circumstances.”--Phil. Trans. for 1846, vol.
cxxxvii.

[34] _New Experiments and Observations on Electricity made at
Philadelphia, in America._--Addressed to Mr. Collinson, from 1747
to 1754. By Benjamin Franklin. Of these Priestley remarks:--“It is
not easy to say whether we are most pleased with the simplicity and
perspicuity with which the author proposes every hypothesis of his own,
or the noble frankness with which he relates his mistakes, when they
were corrected by subsequent experiments.”

[35] “The atomic philosophy of Epicurus, in its mere physical
contemplation, allows of nothing but matter and space, which are
equally infinite and unbounded, which have equally existed from all
eternity, and from different combinations of which every visible form
is created. These elementary principles have no common property with
each other; for whatever matter is, that space is the reverse of; and
whatever space is, matter is the contrary to. The actual solid part of
all bodies, therefore, are matter, their actual pores space, and the
parts which are not altogether solid, but an intermixture of solidity
and pore, are space and matter combined.

“The infinite groups of atoms, flying through all time and space in
different directions and under different laws, have interchangeably
tried and exhibited every possible mode of rencounter: sometimes
repelled from each other by concussion, and sometimes adhering to each
other from their own jagged or pointed construction, or from the casual
interstices which two or more connected atoms must produce, and which
may be just adapted to those of other figures,--as globular, oval, or
square. Hence the origin of compound and visible bodies; hence the
origin of large masses of matter; hence, eventually, the origin of the
world itself.”--Dr. Good’s _Book of Nature_.

[36] Young’s _Lectures on Natural Philosophy and the Mechanical Arts_.
Lecture 49, _On the Essential Properties of Matter_.




CHAPTER V.

CRYSTALLOGENIC FORCES.

  Crystallisation and Molecular Force distinguished--Experimental
    Proof--Polarity of Particles forming a Crystal--Difference
    between Organic and Inorganic Forms--Decomposition
    of Crystals in Nature--Substitution of Particles in
    Crystals--Pseudomorphism--Crystalline Form not dependent
    on Chemical Nature--Isomorphism--Dimorphism--Theories of
    Crystallogenic Attraction--Influence of Electricity and
    Magnetism--Phenomena during Crystallisation--Can a change of
    Form take place in Primitive Atoms?--Illustrative Example of
    Crystallisation.


“Crystallisation is a peculiar and most admirable work of nature’s
geometry, worthy of being studied by all the power of genius, and the
whole energy of the mind, not on account of the delight which always
attends the knowledge of wonders, but because of its vast importance
in revealing to us the secrets of nature; for here she does, as it
were, betray herself, and, laying aside all disguise, permits us
to behold, not merely the results of her operations, but the very
processes themselves.”--Such is the language of an Italian philosopher,
Gulielmini; and it is the striking peculiarity of beholding the process
of the formation of the regular geometric figures of crystals, the
gradual accretion of particle to particle, which induces us to separate
crystallization from mere molecular aggregation. Without doubt the
formation of a crystal and the production of an amorphous block are
due to powers which bear a close resemblance in many points; but they
present remarkable differences in others.

Let us take some simple case in illustration. In quiet water we
have very finely divided matter suspended, and matter in a state of
solution. The first is slowly precipitated, and in process of time
consolidates into a hard mass at the bottom, presenting no particular
character, unless it has been placed in some peculiar physical
conditions; when, as in nature, we have a regular bedding which is
intersected by lines of lamination or of cleavage, which we are, from
experiment, enabled to refer to the influence of current electricity.
The second--the matter in solution--is also slowly deposited; but it is
accumulated upon nuclei which possess some peculiar disposing powers,
and every particle is united by some particular face, and an angular
figure of the most perfect character results. Many pleasing experiments
would appear to show that electricity has much to do in the process
of crystallization; but it is evident that it must be under some
peculiarly modified conditions that this power is exerted, if, indeed,
it has any direct action.

The same substances always crystallize in the same forms, unless the
conditions of the crystallizing body are altered. It has been supposed
that each particle of a crystalline mass has certain points or poles
which possess definite properties, and that cohesion takes place only
along lines which have some relation to the attracting or repelling
powers of these poles. We shall have, eventually, to consider results
which appear to prove that magnetism is universal in its influence, and
that this polarity of the particles of matter may be referred to it.

Be the cause of crystallisation what it may, it presents to us in
appearance a near approach in inorganic nature to some of the peculiar
conditions of growth in the organised creation. In one, we have the
gradual production of parts and the formation of members due to
peculiar powers of assimilation, each individual preserving all its
distinguishing features; and in the other, we have a regular order of
cohesion occurring under the influence of a power which draws like to
like, and arranges the whole into a form of beauty.

This appears to be the proper place for correcting an error too
prevalent, relative to the formation of crystals, the development
of cells, and the yet more fatal falsehood of referring the great
phenomena of Life to any of the physical forces with which we are
acquainted.

THE CRYSTAL _forms_, by the accretion of particle to particle, along
lines determined by some yet unknown power. There is no change in the
character of any particle--like coheres to like; the first atom and the
last of the series being identical in character.

THE PLANT _grows_, not by the gathering together of similar particles
of matter, but by the absorption of a compound particle--by that one
which must be regarded as the primary nuclear atom or cell. After
this absorption--in virtue of a power which we call LIFE, excited
into action by LIGHT--the compound particle is decomposed, and one
constituent is retained to effect the formation of a new cell, whilst
the other is liberated as an invisible air. Here we have a change of
chemical constitution effected; and this takes place through the whole
period of vegetable growth, from the development of the plumule up to
the formation of the latest leaf upon the topmost branch of the most
lordly tree.

Life has been referred to electricity and to chemical power--as the
effect of a known cause. Without doubt, during the operations of life
the whole of the physical powers are necessary to the production of
all the phenomena of growth in the vegetable and the animal world. But
these powers are ever subsidiary to vital force, and are like attendant
spirits chained to do an enchanter’s bidding.

Life is a force beyond the reach of human search, and he who fancies he
has a hold upon the principle which produced biological phenomena, has
committed himself to as wild a pursuit as he who rashly endeavours to
catch a morass-meteor.

Subtile as are the forces of light, heat, and electricity--that of
life, _vitality_, is infinitely more refined, and it must for ever
elude the search of the philosopher.

Man is permitted to test and try all things which are created, and
to apply to useful ends the discoveries which he may make. But man
can never become a creator; and he who would attempt to give sense to
an inert mass of matter, by electricity, heat, or light, will prove
himself as ignorant of nature’s truth as is the senseless mass upon
which he works.

“So far shalt thou go, and no further,” was said equally to the
great tide-wave of human intellect, as to the mighty surge of the
earth-girdling ocean.

It must not be forgotten that a striking difference exists between
the productions of the mineral and the other kingdoms of nature.
Animals and vegetables arrive at maturity by successive developments,
and increase by the assimilation of substances, having the power of
producing the most important chemical changes upon such matter as comes
within the range of their influence; but minerals are equally perfect
in the earliest stages of their formation, and increase only, as
previously said, by the accretion of particles without their undergoing
any change.

The animal and vegetable tribes cease to continue the functions of
life: death ensues, and a complete disorganisation takes place; but
this is not the case in the mineral world: the crystal being the result
of a constantly acting force is not necessarily liable to decomposition.

Nevertheless, we sometimes find in nature that crystals, after arriving
at what may be regarded as, in some sort, their maturity, are, owing
to a change of the conditions under which they were formed, gradually
decomposed. In our mines we discover skeletons of crystals, and
within the hollow shell thus formed, other crystals of a different
constitution and figure find nuclei, and the conditions required for
their development. Again, to give a striking instance, the felspar
crystals of the granitic formations are liable to decomposition in a
somewhat peculiar manner. In decomposing, these crystals leave moulds
of their own peculiar forms, and it not unfrequently happens, in the
stanniferous districts of Cornwall, that oxide of tin gradually fills
these moulds, and we procure this metallic mineral in the form of the
earthy one. Then we have the curious instances of bodies crystallising
in a false form under change of circumstances. We find, for example,
Pseudomorphism, (or _false-form_), as this class of phenomena is named,
occurring by the removal of the constituent atoms of one crystal, while
another set--which naturally assumes a different form--takes their
place, yet still preserving the original shape. It often happens that
copper pyrites will, in this manner, exhibit the angles of an ordinary
variety of crystallised carbonate of iron. These curious changes may
be familiarised by supposing a beautiful statue of gold, from which
some skilful mechanic removes particle by particle, and so skilfully
substitutes a grain of brass for every one of gold removed, that the
loss of the precious metal cannot be detected by any mere examination
of its form.

Crystalline form is not strictly dependent upon the chemical nature
of the parts forming the crystal. The same number of atoms, arranged
in the same way, produce the same form. Substances much unlike each
other will assume the same crystalline arrangement. Magnesia, lime,
oxide of cadmium, the protoxides of iron, nickel, and cobalt, combined
with the same acid, present similarly formed bodies. These Isomorphic
(_like-form_)[37] peculiarities are exceedingly common, and the
discoverer of the phenomena, Mitscherlich, announced the above law.
It cannot, however, be regarded as a philosophical expression of the
fact, and requires reconsideration--chemical elements of a dissimilar
character may have the same law of aggregation, and thus produce the
same form, without having any relation to the number of atoms.

We also find compounds which have two distinct systems of
crystallisation. This property, Dimorphism, is very strikingly shown
in carbonate of lime, which occurs in rhombohedrons, in calc spar, and
in rhombic prisms in arragonite. The molecular arrangements here are
not, however, of equal stability, and one form is evidently forced upon
the other, and is abandoned by it on the slightest disturbance. When a
prism of arragonite is heated it breaks up into the rhombs of common
calc spar, at a temperature far below that at which the carbonate of
lime is decomposed; but no alteration of temperature can convert calc
spar into arragonite.

Crystals are found in the most microscopic character, and of an
exceedingly large size. A crystal of quartz at Milan is three feet and
a quarter long, and five feet and a half in circumference, and its
weight is 870 pounds. Beryls have been found in New Hampshire measuring
four feet in length.[38]

In the dark recesses of the earth, where the influences which produce
organisation and life cease to act, a creative spirit still pursues its
never-ending task of giving form to matter.

The science of crystallogeny,[39] embracing the theoretical and
practical question of the causes producing these geometric forms,
has in various ways attempted to explain the laws according to which
molecules arrange themselves on molecules in perfect order, giving rise
to a rigidly correct system of architecture. But it cannot be said that
any theory yet propounded is sufficiently exact to embrace the whole
of the known phenomena, and the questions,--What is crystallogenic
attraction, and what is the physical nature of the ultimate particles
of matter,--are still open for the inquiries of that genius which
delights in wrestling with the secrets of nature.

The great Epicurus speculated on the “plastic nature” of atoms, and
attributed to this _nature_ the power they possess of arranging
themselves into symmetric forms. Modern philosophers satisfy themselves
with attraction, and, reasoning from analogy, imagine that each atom
has a polar system.

Electricity, and light, and heat, exert remarkable powers, and
accelerate or <DW44> crystallisation according to the conditions under
which these forces are brought to bear on the crystallising mass. We
have recently obtained evidence which appears to prove that some form
of magnetism has an active influence in determining the natural forms
of crystals, and we discover that magnetism exerts a peculiar influence
in relation to the optic axes of crystals, which is not exerted in
lines at right angles to these. Electricity appears to quicken the
process of crystalline aggregation--to collect more readily together
those atoms which seek to combine--to bring them all within the limits
of that influence by which their symmetrical forms are determined; and
strong evidence is now afforded, in support of the theory of magnetic
polarity, by the refined investigations of Faraday and Plücker, which
prove that magnetism has a _directing_ influence upon crystalline
bodies.[40]

It has been found that crystals of sulphate of iron, slowly forming
from a solution which has been placed within the range of sufficiently
powerful magnetic force, dispose themselves along certain magnetic
curves, such as are formed around a magnet by steel filings; whereas
the crystals of the Arbor Dianæ, or silver tree, forming under the
same circumstances, take a position nearly at right angles to these
curves. Certain groups of crystals have been found in nature, which
appear to show, by their positions, that terrestrial magnetism has been
active in producing the phenomena they exhibit; indeed, nearly all our
mineral formations indicate the influences of this, or some similarly
acting power.[41]

During rapid crystallisation, some salts--as the sulphate of
soda, boracic acid, and arsenious acid crystallising in muriatic
acid--exhibit decided indications of electrical excitement; light is
given out in flashes. We have evidence that crystals exhibit a tendency
to move towards the light, and that crystallisation takes place more
readily, and progresses with greater activity in the sunshine than in
the shade. Professor Plücker has recently ascertained that certain
crystals--in particular the cyanite--“point very well to the north,
by the magnetic power of the earth only. It is a true compass needle;
and, more than that, you may obtain its declination.” We must remember
that this crystal, the cyanite, is a compound of silica and alumina
only. This is the amount of experimental evidence which science has
afforded in explanation of the conditions under which nature pursues
her wondrous work of crystal formation. We see just sufficient of
the operation to be convinced that the luminous star which shines in
the brightness of Heaven, and the cavern-secreted gem, are equally
the result of forces which are known to us in only a few of their
modifications.

Every substance, when placed under circumstances which allow of the
free movement of its molecules, has a tendency to crystallise. All the
metals may, by slowly cooling from the melting state, be exhibited
with a crystalline structure. Of the metallic and earthy minerals,
nature furnishes us with an almost infinite variety of crystals, and,
by a reduction of temperature, yet more simple bodies assume the
most symmetric forms. Water, in the conditions of ice and snow, is a
familiar and beautiful example; and, by such extreme degrees of cold as
are artificially produced, many of the gases exhibit a tendency to a
crystalline condition.

May not the solid elementary atoms be susceptible of change of form
under different influences? May not the different states under which
the same bodies are found--as, for example, silica, carbon, and
iron--be due entirely to a change in the form of the primitive atom?

Admitting the probability of this, we then easily see that the central
molecule, formed of an aggregation of such atoms, uniting by particular
faces, would present a determinate form; and that the resulting
crystal, a mass of such molecules, cohering according to a given law,
at certain angles, would present such geometric figures as we find in
nature, or produce in our laboratories, when we avail ourselves of
processes which nature has taught us.

If we take a particle of marble, and place it in a large quantity
of water acidulated with sulphuric acid, it dissolves, and a new
compound results. The marble disappears--the eye cannot detect it by
form or colour: the acid also has been disguised--the taste discovers
nothing sour in the fluid. We have, in combination with the water,
the lime and sulphuric acid; but that combination appears to the eye
in no respect different from the water itself. It is colourless and
perfectly transparent, although it holds a mass of solid matter which
previously would not allow of the permeation of a ray of light. Let
us expose this fluid to such circumstances that the water will slowly
evaporate, and we shall find forming in it, after a time, microscopic
particles of solid, light-refracting matter. These particles gradually
increase in size, and we may watch their growth until eventually we
have a symmetric figure, beautifully shaped, the primary form of
which is a right rhomboidal prism. Thus in nature, by the action,
in all probability, of vegetable matter on the sulphates held in
solution by the water of the great rivers and the ocean--aided by our
oxidizing atmosphere--sulphuric acid is produced to do its work upon
the limestone formations, and from this combination would result the
well-known gypsum, or plaster of Paris, which ordinarily exists as an
amorphous mass, but is often found in a crystalline form.[42]

This is a very perfect illustration of the wonderful process we have
been considering, and in which, simple though it appears to be, we
have set to work a large proportion of the known physical elements
of the universe. By studying aright the result which we have it in
our power to obtain in a watch-glass, we may advance our knowledge of
gigantic phenomena, which are now progressing at the bottom of the
ocean, or of the wondrous agencies which are in operation, producing
light-refracting gems within the secret recesses of the rocky crust of
our globe.

The force of crystallisation is a subject worthy of much consideration.
If we examine our slate rocks, through which little veins filled with
quartz crystals are spread, we shall see that the mechanical force
exerted during the production of these crystals has been capable of
rending those rocks in every direction. Those fissures formed by the
first system of crystalline veins, in order of time, are filled in by
another set of crystalline bodies, which equally exert their mechanical
power, and thus produce those curious intersections and dislocations
which were long a puzzle to the geologist. The simplest power, slowly
and constantly acting through a long period of time, may become
sufficient, eventually, to rend the Andes from base to summit, or to
lift a new continent above the waters of the ocean.


FOOTNOTES:

[37] “Gay Lussac first made the remark, that a crystal of potash alum,
transferred to a solution of ammonia alum, continued to increase
without its form being modified, and might thus be covered with
alternate layers of the two alums, preserving its regularity and proper
crystalline figure. M. Beudant afterwards observed that other bodies,
such as the sulphates of iron and copper, might present themselves
in crystals of the same form and angles, although the form was not a
simple one, like that of alum. But M. Mitscherlich first recognised
this correspondence in a sufficient number of cases to prove that it
was a general consequence of similarity of composition in different
bodies.”--Graham’s _Elements of Chemistry_ (1842), p. 136.

The following remarks are from a paper by Dr. Hermann Kopp, _On the
Atomic Volume and Crystalline Condition of Bodies, &c._, published in
the Philosophical Magazine for 1841:--“The doctrine of isomorphism
shows us that there are many bodies which possess an analogous
constitution, and the same crystalline form. Our idea of the volume
(or, in other words, of the crystalline form) of these bodies must
therefore be the same. From this it follows that their specific
weight is connected with mass contained in the same volume. From
these considerations the following law may be deduced: _The specific
weight of isomorphous bodies is proportional to their atomic weight,
or isomorphous bodies possess the same atomic volume_.”--page 255.
A translation appears in the Cavendish Society, from Dr. Otto’s
Chemistry, _On Isomorphism_, which may be advantageously consulted. See
also a paper by M. Rose, translated from the _Proceedings of the Royal
Berlin Academy_ for the _Chemical Gazette_, Oct. 1848, entitled, _On
the Isomeric Conditions of the Peroxide of Tin_.

[38] _A System of Mineralogy, comprising the most recent discoveries_,
by James D. Dana, A.M., New York, 1844.

[39] Crystallogeny, or the formation of crystals, is the term employed
by Dana, in his admirable work quoted above: whose remarks on
_Theoretical Crystallogeny_, p. 71, are well worthy of all attention.

[40] _On the Magnetic Relations of the Positive and Negative Optic Axes
of Crystals_, by Professor Plücker, of Bonn.--Philosophical Magazine,
No. 231 (3rd Series), p. 450. _Experimental Researches on Electricity;
On the Crystalline Polarity of Bismuth and other bodies, and on its
Relation to the Magnetic form of Force_: by Michael Faraday, Esq.,
F.R.S.--Transactions of the Royal Society for 1848.

[41] In the _Memoirs of the Geological Survey of the United Kingdom,
and of the Museum of Economic Geology_, vol. i. 1846, will be found a
paper, by the author of this volume, _On the Influences of Magnetism on
Crystallisation, and other Conditions of Matter_, in which the subject
is examined with much care. See also _Magnétisme polaire d’une montagne
de Chlorite schisteuse et de Serpentine_: Annales de Chimie, vol. xxv.
p. 327; _Influence du Magnétisme sur les actions chimiques_, by l’Abbé
Rendus; and also a notice of the experiments of Ritter and Hansteen,
“Analysées par M. Œrsted;” also _Effets du Magnétisme terrestre sur
la précipitation de l’Argent, observés par M. Muschman_: Annales de
Chimie, vol. xxxviii. p. 196-201.

[42] The transparent varieties of sulphate of lime are distinguished
by the name _Selenite_; and the fine massive varieties are called
_Alabaster_. Gypsum forms very extensive beds in secondary countries,
and is found in tertiary deposits; occasionally, in primitive rocks; it
is also a product of volcanoes. The finest foreign specimens are found
in the salt mines of Bex, in Switzerland; at Hall, in the Tyrol; in the
sulphur-mines of Sicily; and in the gypsum formation near Ocana, in
Spain. In England, the clay of Shotover Hill, near Oxford, yields the
largest crystals.--See Dana’s _Mineralogy_, second edition, p. 241.




CHAPTER VI.

HEAT--SOLAR AND TERRESTRIAL.

  Solar and Terrestrial Heat--Position of the Earth in the Solar
    System--Heat and Light associated in the Sunbeam--Transparency
    of Bodies to Heat--Heating Powers of the  Rays of
    the Spectrum--Undulatory Theory--Conducting Property of the
    Earth’s Crust--Convection--Radiation--Action of the Atmosphere
    on Heat Rays--Peculiar Heat Rays--Absorption and Radiation
    of Heat by dissimilar Bodies--Changes in the Constitution of
    Solar Beam--Differences between Transmitted and Reflected
    Solar Heat--Phenomena of Dew--Action of Solar Heat on the
    Ocean--Circulation of Heat by the Atmosphere and the Ocean--Heat
    of the Earth--Mean Temperature--Central Heat--Constant Radiation
    of Heat Rays from all Bodies--Thermography--Action of Heat on
    Molecular Arrangements--Sources of Terrestrial Heat--Latent
    Heat of Bodies--Animal Heat--Eremacausis--Spheroidal State
    Cold--Condensation--Freezing--Theories of Heat--Natural
    Phenomena--and Philosophical Conclusion.


We receive heat from the sun, associated with light; and we have the
power of developing this important principle by physical, mechanical,
and chemical excitation, from every kind of matter. Our convictions
are, that the calorific element, whether derived from a solar or a
terrestrial source, presents no essential difference in its physical
characters; but as there are some remarkable peculiarities in the
phenomena, as they arise from either one or the other source, it will
assist our comprehension of this great principle, if we consider it
under the two heads.

Untutored man finds health and gladness in the warmth and light of the
sun; he rears a rugged altar, and bows his soul in prayer, to the
principle of fire, which in his ignorance he regards as the giver and
the supporter of life. The philosopher finds life and organization
dependent upon the powers combined in the sunbeam; and, examining
the phenomena of this wonderful band of forces, he is compelled to
acknowledge that the flame upon the altar--on the Persian hills,--was
indeed a dim shadow of the infinite wisdom which abides behind the veil.

The present condition of our earth is directly dependent upon the
amount of heat we receive from the sun. It has frequently been said,
that if it were possible to move this planet so much nearer that orb
that the quantity of heat would be increased, the circumstances of
life would necessarily be so far changed, that all the present races
of animals must perish; and that the same result would happen from
any alteration which threw us yet further from our central luminary,
when, owing to the extremity of cold and the wretchedness of gloom, all
living creatures would equally fail to support their organization.

To move the earth nearer to, or more distant from the sun, is an
impossibility; but it has been argued that those planets which are near
to the sun must possess a temperature which would melt our solid rocks,
and vaporize the ocean,--while Uranus and Neptune must, from their
distance from the source of heat, have so small an amount, that water
must become solid as the rock, and such an atmosphere as that of the
earth exist as a dense liquid.

It will be shown that according to the physical condition of the
material substances, so are their powers regulated of absorbing and
retaining the heat which falls as a radiant power upon their surfaces.
Heat rays, in passing through the attenuated medium of planetary space,
lose none of their power--this we know from the fact that even the less
dense upper region of the earth’s atmosphere takes from the solar rays
but an exceedingly small quantity of heat. Therefore, whether a solar
heat ray traverses through one million, or one hundred million miles of
space, it still retains its power equally of imparting warmth to the
solid matter by which it is intercepted. There is no law of variation
as the inverse square of the distance of those radiating powers.
Consequently, there is no reason why the physical conditions, alike
of the nearest and the most remote planetary bodies, should not be so
adjusted that they all enjoy that life promoting temperature which
belongs to the earth.

All the objects around us are adapted to the circumstances of the
earth’s position in relation to the sun, to which we are bound by the
principle of gravitation; opposed to that centrifugal force which tends
constantly to drive the moving planetary mass off from the centre of
power. The balance maintains its perfect equilibrium, although we have
one power constantly drawing the earth towards the sun, and the other
as constantly exerting itself to move it off into space at a tangent
to the orbit in which the planet moves. In our examination it will be
found that one common system of harmony runs through all the cosmical
phenomena, by which everything is produced that is so beautiful and
joyous in this world.

Heat, and the other elementary radiant principles, are often combined
as the common cause of effects evident to our senses. The warmth of the
solar rays, and their luminous influence, are not, however, commonly
associated in the mind as the results of a single cause. It is only
when we come to examine the physical phenomena connected with these
radiations that we discover the complexity of the inquiry. Yet it is
out of these very subtle researches that we draw the most refined
truths. The high inferences to which the analysis of the subtile
agencies of creation leads us, render science, pursued in the spirit of
truth, a great system of religious instruction.

Although we do not fear that heat and light can be confounded in the
mind, so different are their phenomena,--we have heat rays, as from
dark hot iron, which give no light, while in the full flood of the
lunar rays the heat is scarcely appreciable by the most delicate
instruments;--yet it is important to show how far these two principles
have--been separated from each other. Transparent bodies have varied
powers of calorific transparency, or transcalescence: some obstructing
the heat radiated from bodies of the highest temperatures almost
entirely even in the thinnest layers; whilst others will allow the
warmth of the hand to pass through a thickness of several inches.
Liquid chloride of sulphur, which is of a deep red colour, will allow
63 out of 100 rays of heat to pass, and a solution of carmine in
ammonia, or glass stained with oxides of gold, or copper, rather a
greater number; yet these transparent media obstruct a large quantity
of light. Colourless media obstructing scarcely any light, will, on
the contrary, prevent the passage of calorific rays. Out of every
hundred rays, oil of turpentine will only transmit 31, sulphuric ether
21, sulphuric acid 17, and distilled water only 11. Pure flint glass,
however, is permeated by 67 per cent. of the thermic rays, and crown
glass by 49 per cent. The body possessing the most perfect transparency
to the rays of heat is diaphanous salt-rock, which transmits 92, while
alum, equally translucent, admits the passage of only 12 per cent.[43]

Black mica, obsidian, and black glass, are nearly opaque to light, but
they allow 90 per cent. of radiant heat to pass through them; whereas
a pale green glass,  by oxide of copper,[44] covered with a
layer of water, or a very thin plate of alum, will, although perfectly
transparent to light, almost entirely obstruct the permeation of heat
rays.

We thus arrive at the fact that heat and light may be separated from
each other; and if we examine the solar beam by that analysis which the
prism affords, we shall find that there is no correspondence between
intense light and ardent heat. By careful observation, it has been
proved, when we have a temperature of 62° F. in the yellow ray, which
ray has the greatest illuminating power; that below the red ray, out of
the point of visible light, the temperature is found to be 79°, while
at the other end of the spectrum, in the blue ray, it is 56°, and at
the end of the violet ray no thermic action can be detected.[45]

From the circumstance, that as we, by artificial means, raise the
temperature of any body, and produce intense heat, so after a
certain point of thermic elevation has been obtained, we occasion a
manifestation of _light_.[46] It has been concluded, somewhat hastily,
that heat and light differ from each other only in the rapidity of the
undulations of an hypothetical ether.

It must be admitted that the mathematical demonstrations of many of the
phenomena of calorific and luminous power are sufficiently striking to
convince us that a wave-movement is common to both heat and light. The
undulatory theory, however, requires the admission of so many premises
of which we have no proof; its postulates are, indeed, in many cases
so gratuitous, that notwithstanding the array of talent which stands
forward in its support, we must not allow ourselves to be deceived by
the deductions of its advocates, or dazzled by the brilliancy of their
displays of learning.

Radiant heat appears to move in waves; but that calorific effects in
material bodies are established by any system of undulation, is a
deduction without a proof; and the thermic phenomena of matter are as
easily explained by the hypothesis of a diffusive subtile fluid.

We have not, however, to prove the correctness of either of the
opposing views; indeed, it is acknowledged that many phenomena require
for their explanation conditions which are not indicated by either
theory.

The earth receives its heat from the sun; a portion of it is
_conducted_ from particle to particle into the interior of the rocky
crust. Another portion produces warmth in the atmosphere around us,
by _convection_, or the circulation of particles; those warmed by
contact with the surface becoming lighter, and ascending to give place
to the colder and heavier ones. A third portion is radiated off into
space, according to laws which have not been sufficiently investigated,
but which are dependent upon the colour, chemical composition, and
mechanical structure of the surface.

It cannot but be instructive to contemplate the indications which we
have of the dependence of all that is beautiful on earth, on the heat
and light radiations which we receive from the sun. Let us endeavour
to realise some of the effects which arise from even the temporary
deprivation of solar heat.

It is winter, the vegetable world appears chilled to its centre. The
trees, except a few of the hardy evergreens, are bare of leaves, and
stretching forth their branches into the cold air, they realise the
condition of vegetable skeletons. The lowly plants of the hedge-row,
and the grasses of the field, show that their vital power is subdued
to that minimum degree of action which is but a few slight removes
from death. The life of the running stream is suspended, it is cased
in the “thick-ribbed ice,” and the waters beneath no longer send forth
their joyous music to the genial breeze. Even within the temperate
limits of our own land, the aspect of winter convinces the ordinary
observer, that the loss of heat has been followed by diminished
activity in the powers of life; and the philosopher discovers that the
lessened energies of solar light, and the weaker action of the radiant
heat, have aided in producing that repose which is a little more than
sleep--a little less than death.

It is night, and winter: the earth is parting with its heat,--with
the absence of light, there is a still greater loss of vigour, a yet
further diminution of the powers of life. Even the animal races,
sustained by vital influences of a more exalted kind, sink under the
temporary deprivation of the solar rays to a monotonous, a melancholy
repose. All animals undergo different degrees of hybernation, and
each in his winter retreat supports vitality by preying upon himself.
The world is hung in mourning black; there is no play of colours to
harmonize the human spirit by sending their ethereal pulsations to the
human eye, and it is only the consciousness that when the night is at
the darkest, the day is nearest, that even man’s soul is sustained
against the depressing influences of the absence of the sun.

The conditions which we must observe at our own doors cannot fail to
convey as a conviction to the least imaginative mind, that a slightly
prolonged continuance of darkness, with its consequent increase of
coldness, would be fatal to the existence of the organic world.

The sun has entered Aries: it is spring. The length of the day and
night are equal, the powers of light and darkness are now exactly
balanced against each other, and light, like the Archangel, triumphs
over the sombre spirit. The organic world awakes. Chemical action
commences in the seed, the vital spark is kindled in the embryo, and
under the impulsive force of some solar radiations the plant struggles
into light and life. The same invigorating force impels the circulation
of the sap through the capillary tubes of the forest tree, until the
topmost branch trembles with the new flow of life. The buds burst forth
into leaf, and a fresh and lively covering spreads over those branches
which, in their nakedness, could scarcely be distinguished from the
dead.

The animal races are no less sensible of the new influence which is
diffused around. The birds float joyously upon the breeze, and give
to heaven their trilling songs of praise. The beasts come forth from
the clefts of the rocks and the tangled shelters of the forests, and
gambol in the full luxury of their renewed vigour. Man, even man, the
inhabitant of cities, trained and tempered to an artificial state,
awakes of a spring morning with a fuller consciousness of mind, and a
deeper and more pleased sense of his intelligence, than when the fogs
and gloom of winter hung like the charmed robe upon the limbs of the
giant. Now, the dormant poetry of man seeks expression. As the morning
sun is said to have awakened the musical undulations of the Memnonian
statue, so the sun of the vernal morning produces in the mind of the
most earthly, faint pulsations of that heaven-born music, which neither
sin nor sorrow can entirely destroy. The psychologist, in studying the
peculiar phenomena of the human mind, must associate himself with the
natural philosopher, and learn to appreciate the influence of physical
causes in determining effects which our elder philosophers and the
poets of every age have attributed to spiritual agencies.

Summer, with its increased heat and light, reigns over the land. The
work of life is now at its maximum, and every energy is quickened
throughout the organic creation. The laws of nature are arranged
on the principle of antagonistic forces, the constant struggle to
maintain them in equilibrium constituting the sensible phenomena of
existence. Heat and light, with chemical power and electricity, have
been quickening the unknown principle of life, until it has become
exhausted in the production of new parts--in the strange phenomenon of
growth--the formation of organized matter from the inorganic stores of
creation.

The autumn, with its tempered sunlight, comes, but in the solar
radiance we discover new powers, and under the influence of these the
flower and the fruit have birth. The store of a new life is centered in
the seed, and though the leaf falls, and the flower fades, a new set
of organisms are produced, by which the continuance of the species is
secured.

Let any man examine himself as the seasons change, and he will soon be
convinced that every alternation of light and darkness, of heat and
its absence, produces new sets of influences equally on the mind and
on the body, showing the entire dependence of the animal and vegetable
kingdoms upon those causes which appear to flow from the centre of our
planetary system.

The phenomena which connect themselves with the changes of the seasons
cannot fail to convince the most superficial thinker that there is an
intimate connection between the sun and the earth which deserves our
close attention.

Indeed, if we examine the most ancient of histories, we find one great
fact at the base of all their philosophies. Moses connects darkness
with a void and formless earth, and light with the creation of harmony
and life. Menis sings of a fearful world by “many formed darkness
encircled,” and links the idea of a “life-breathing divinity” with the
awakening of light upon created things. The Egyptian Isis, the Grecian
Apollo, who,

    The Lord of boundless light
    Ascending calm o’er the empyrean sails,
    And with ten-thousand beams his awful beauty veils,

the fire-worshipper of the Persian hills and the sun-god of the
Peruvian mountains, exhibit, through time and space, the full
consciousness of man to the influences of solar light and heat upon the
organic creations of which he is himself the chief exemplar.

The investigations of modern philosophers have extended these
influences to the inorganic masses which constitute the Planet
EARTH:--and we now know that the physical forces, ever active in
determining the chemical condition and the electrical relations of
matter, are directly influenced by the solar radiations.

Few things within the range of our inquiry are more striking than
the phenomena of calorific radiation and absorption. They display so
perfectly the most refined system of order, and exhibit so strikingly
the admirable adaptation of every formation to its particular
conditions, and for its part in the great economy of being, that they
claim most strongly the study of all who would seek to discover a
poetry in the inferences of science.

Owing to the nature of our atmosphere, we are protected from the
influence of the full flood of solar heat. The absorption of caloric by
the air has been calculated at about one-fifth of the whole in passing
through a column of 6,000 feet. This estimate is, of course, made near
the earth’s surface; but we are enabled, knowing the increasing rarity
of the upper regions of our gaseous envelope in which the absorption
is constantly diminishing, to prove, that about one-third of the solar
heat is lost by vertical transmission through the whole extent of our
atmosphere.[47]

Experience has proved that the conditions of the sun’s rays are not
always the same; and there are few persons who have not observed that
a more than usual scorching influence prevails under some atmospheric
circumstances. This is also evidenced in the effects produced on the
foliage of trees, which, though often attributed to electricity, is
evidently due to heat. An examination of the solar radiations, as
exhibited in the prismatic spectrum, has proved the existence of a
class of heat rays, which manifest themselves by a very peculiar
deoxidizing power quite independent of their caloric properties,
to which the name of _parathermic rays_ has been given.[48] We are
protected from the severe effects of these rays by the ordinary state
of the medium through which the solar heat passes. Our atmosphere is a
mixture of gases and aqueous vapour; and it has been found, as already
stated, that even a thin film of water, however transparent, prevents
the passage of many calorific radiations, and the rays retarded are,
for the most part, of that class which have this peculiar scorching
power. The air is, in this way, the great equaliser of the solar
heat, rendering the earth agreeable to all animals, who, but for this
peculiar absorbent medium, would have to endure, even in our temperate
clime, the burning rays of a more than African sun.

The surface of the earth during the sunshine--and, though in a less
degree, even when the sun is obscured by clouds--is constantly
receiving heat; but the rate of its absorption varies. Benjamin
Franklin showed, by a set of simple but most conclusive experiments,
that a piece of black cloth was warmed much sooner than cloth of a
lighter colour;[49] and we know, from observations of a similar class,
that the bare brown soil receives heat more readily than the bright
green grassy carpet of the earth. Consequently, during the winter
season, relatively to the quantity poured from its source, more heat
penetrates the uncovered soil, than during the spring or summer.

There is a constant tendency to an equilibrium; and, during the night,
the surface is robbed of more heat, by the colder air, than by day; as,
when the earth is not receiving heat, it is constantly radiating it
back into space. Even in these processes of convection and radiation, a
similar law prevails to that which is discovered in examining into the
rate of calorific absorption.

Every tree spreading its green leaves to the sunshine, or exposing
its brown branches to the air--every flower which lends its beauty to
the earth--possesses different absorbing and radiating powers. The
chalice-like cup of the pure white lily floating on the lake--the
variegated tulip--the brilliant anemony--the delicate rose--and the
intensely  peony or dahlia--have each powers peculiar to
themselves for drinking in the warming life-stream of the sun, and
for radiating it back again to the thirsting atmosphere. These are
no conceits of a scientific dreamer; they are the truths of direct
induction; and, by experiments of a simple character, they may be put
to a searching test.[50]

A thermometric examination of the various  flowers, by
enclosing a delicate thermometer amongst their leaves, will readily
establish the correctness of the one; and by a discovery of recent
date, connected with calorific radiation, which must be particularly
described presently, we can, with equal ease and certainty, test the
truth of the other;[51] the absorption and radiation of heat being
directly regulated by the colours of the surfaces upon which the sun
rays fall.

It follows, as a natural consequence of the position of the sun, as
it regards any particular spot on the earth at a given time, that the
amount of heat is constantly varying during the year. This variation
regulates the seasons.

When it is remembered that the earth is, in the winter, nearly three
millions of miles nearer the sun than in the summer, some explanation
is required to account for our suffering more cold when nearer the
source of heat, than when at the remotest distance.

The earth in her path around the sun describes an ellipse, the
sun’s place being one of its foci. In obedience to the law, already
described, of the conservation of the axis of rotation, the axis of
the earth constantly points towards the star in the constellation of
the Little Bear. Recollecting this, and also the two facts, that a
dense solid body absorbs heat more readily than a fluid one, and that
radiation from the surface is constantly going on when absorption is
not taking place, let us follow the earth in her orbit.

It is the time of the vernal equinox--we have equal day and
night--therefore the periods of absorption and radiation of heat are
alike. But at this time of the year the southern hemisphere is opposite
to the sun, consequently the degree of absorption by the wide-spread
oceans small.

It is the summer solstice--we have sixteen hours of daylight, when the
absorption of heat is going on--and but eight hours of night, during
which heat is passing off. The northern hemisphere is now presented
to the sun, and as here we have the largest portion of dry land, the
powers of absorption are at their maximum.

The autumnal equinox has arrived, with its equal day and night, as in
the spring, but now the whole northern hemisphere is opposite the sun;
hence, according to the laws already explained, we see the causes of
the increased heat of the autumnal season.

The winter solstice has come, with its long night and shortened day.
The time during which radiation is going on is nearly twice that in
which absorption takes place, and the earth is in her worst position
for receiving heat, as that half which has the largest surface of water
is towards the sun.

These are the causes which lead to the variations of the seasons, and
through these we learn why we are colder when near the sun than when at
a considerably greater distance.

An analysis of the spectrum shows us that there are some changes
regularly taking place in the state of the solar beam, which cannot
be referred to the mere alteration of position. It may be inferred,
from facts by long-continued observations, that the three classes of
phenomena--light, heat, and chemical power, distinguished by the term
Actinism--which we detect in the sun’s rays, are constantly changing
their relative proportions. In spring, the chemical agency prevails; in
summer, the luminous principle is the most powerful; and in the autumn,
the calorific forces are in a state of the greatest activity.[52] The
importance of these variations, to the great economy of vegetable life,
will be shown when we come to examine the phenomena connected with
organisation.

A remarkable change takes place in the character of heat in being
reflected from material substances. In nature we often see this fact
curiously illustrated. Snow which lies near the trunks of trees or
wooden poles melts much quicker than that which is at a distance from
them, the sun shining equally on both--the liquefaction commencing on
the side facing the sun, and gradually extending. We see, therefore,
that the direct rays of solar heat produce less effect upon the snow
than those which are radiated from  surfaces. By numerous
experiments, it has been shown that these secondary radiations are
more abundantly absorbed by snow or white bodies than the direct solar
rays themselves. Here is one of the many very curious evidences, which
science lays open to us, of the intimate connection between the most
ethereal and the grosser forms of matter. Heat, by touching the earth,
becomes more earth-like. The subtile principle which, like the spirit
of superstition, has the power of passing, unfelt, through the crystal
mass, is robbed of its might by embracing the things of earth; and
although it still retains the evidences of its refined origin, its
movements are shackled as by a clog of clay, and its wings are heavy
with the dust of this rolling ball. It has, however, acquired new
properties, which fit it for the requirements of creation, and by which
its great tasks are facilitated. Matter and heat unite in a common
bond, and, harmoniously pursuing the necessities of some universal law,
the result is the extension of beautiful forms in every kingdom of
nature.

An easy experiment pleasingly illustrates this remarkable change. If a
blackened card is placed upon snow or ice in the sunshine, the frozen
mass underneath it will be gradually thawed, and the card sink into
it, while that by which it is surrounded, although exposed to the full
power of solar heat, is but little disturbed. If, however, we reflect
the sun’s rays from a metal surface, an exactly contrary result takes
place; the uncovered parts are the first to melt, and the blackened
card stands high above the surrounding portion.

The evidences of science all indicate the sun as the source, not only
of that heat which we receive directly through our atmosphere, but
even of that which has been stored by our planet, and which we can,
by several methods, develope. We have not to inquire if the earth was
ever an intensely heated sphere;--this concerns not our question; as
we should, even were this admitted, still have to speculate on the
origin--the primitive source of this caloric.

Before, however, we proceed to the examination of the phenomena of
terrestrial heat, a few of the great results of the laws of radiation
and convection claim our attention.

Nearly all the heat which the sun pours upon the ocean is employed in
converting its water into vapour at the very surface, or is radiated
back from it, to perform the important office of producing those
disturbing influences in the atmosphere, which are essential to the
preservation of the healthful condition of the great aërial envelope in
which we live.

Currents of air are generally due to the unequal degrees in which the
atmosphere is warmed. Heat, by expanding, increases the elasticity,
and lessens the density, of a given mass. Consequently, the air heated
by the high temperature of the tropics, ascends charged with aqueous
vapours, whilst the colder air of the temperate and the frigid zones
flows towards the equator to supply its place. These great currents of
the atmosphere are, independent of the minor disturbances produced by
local causes, in constant flow, and by them a uniformity of temperature
is produced, which could not in any other way be accomplished. By these
currents, too, the equalisation of the constituents of the “breath
of life” is effected, and the purer oxygen of the “land of the sunny
south” is diffused in healthful gales over the colder climes of the
north. The waters, too, evaporated from the great central Atlantic
Ocean, or the far Pacific, are thus carried over the wide-spread
continents, and poured in fertilising showers upon distant lands.

How magnificent are the operations of nature! The air is not much
warmed by the radiations of caloric passing from the sun to the earth;
but the surface soil is heated by its power of absorbing these rays.
The temperature of the air next the earth is raised, and we thus have
the circulation of those beneficial currents which are so remarkably
regular in the Trade Winds. The air heated within the tropics would
ascend directly to the poles, were the earth at rest, but being in
motion, those great aërial currents--the Trade Winds--are produced,
and the periodical monsoons are due to the same cause. A similar
circulation, quite independent of the ordinary tidal movement,
takes place also in the earth-girdling ocean. The water, warmed, by
convection, from the hot surface of the tropical lands, sets across
the Atlantic from the Gulf of Mexico; and being under the influence of
the two forces--gravity and motion--it illustrates the parallelogram
of forces, and flowing along the diagonal, reaches our own shores: the
genial influences of the gulf stream produce that tempered climate
which distinguishes our insular home. Here we have two immense
influences produced by one agency, rendering those parts of the earth
habitable and fertile, which but for these great results would sorrow
in the cheerless aspect of an eternal winter.

The beautiful phenomenon of the formation of dew is also distinctly
connected with the peculiar properties which we have been studying.
When from the bright blue vault of heaven, the sparkling constellations
shower their mild light over the earth, the flowers of the garden
and the leaves of the forest become moist with a fluid of the most
translucid nature. Well might the ancients imagine that the dews were
actually shed from the stars; and the alchemists and physicians of the
middle ages conceive that this pure distillation of the night possessed
subtile and penetrating powers beyond most other things; and the
ladies of those olden times endeavour to preserve their charms in the
perfection of their youthful beauty through the influences of washes
procured from so pure a source.[53]

Science has removed the veil of mystery with which superstition had
invested the formation of dew; and, in showing to us that it is
a condensation of vapour upon bodies according to a fixed law of
radiation, it has also developed so many remarkable facts connected
with the characters of material creations, that a much higher order of
poetry is opened to the mind than that which, though beautiful, sprang
merely from the imagination.

Upon the radiation of heat depends the formation of dew, and bodies
must become colder than the atmosphere before it will be deposited
upon them. At whatever temperature the air may be, it is charged to
saturation with watery vapour, the quantity varying uniformly with
the temperature. Supposing the temperature of the air to be 70° F.,
and that a bottle of water at 60° is placed in it, the air around
the bottle will be cooled, and will deposit on the glass exactly
that quantity of moisture which is due to the difference between the
temperature of the two bodies. Different substances, independent of
colour, have the property of parting with heat from their surfaces at
different rates. Rough and porous surfaces radiate heat more rapidly
than smooth ones, and are consequently reduced in temperature; and, if
exposed, are covered with dew sooner than such as are smooth and dense.
The grass parterre glistens with dew, whilst the hard and stony walk is
unmoistened.[54]

Colourless glass is very readily suffused with dampness, but polished
metals are not so, even when dews are heavily condensed on other
bodies. To comprehend fully the phenomena of the formation of dew,
we must remember that the entire surface of the earth is constantly
radiating heat into space; and that, as by night no absorption is
taking place, it naturally cools.[55] As the substances spread over
the earth become colder than the air, they acquire the power of
condensing the vapour with which the atmosphere is always charged. The
bodies which cover this globe are very differently constituted; they
possess dissimilar radiating powers, and consequently present, when
examined by delicate thermometers, varying degrees of temperature. By
the researches of Dr. Wells,[56] which may be adduced as an example of
the best class of inductive experiments, we learn that the following
differences in sensible heat were observed at seven o’clock in the
evening:--

    The air four feet above the grass      60-3/4
    Wool on a raised board                 54-1/2
    Swandown on ditto                      53
    The surface of the raised board        57
    Grass plat                             51

Dew is most abundantly deposited on clear, calm nights, during which
the radiation from the surface of the earth is uninterrupted. The
increased cold of such nights over those obscured by clouds is well
known. The clouds, it has been proved, act in the same way as the
screens used by gardeners to protect their young plants from the
frosts of the early spring, which obstruct the radiation, and, in all
probability, reflect a small quantity of heat back to the earth.

It is not improbable that the observed increase in grass crops, when
they have been strewn with branches of trees or any slight shades, may
be due to a similar cause.[57]

There are many remarkable results dependent entirely on the colours
of bodies, which are not explicable upon the idea of difference in
mechanical arrangement. We know that different colours are regulated
by the powers which structures have of absorbing and reflecting light;
consequently a blue surface must have a different order of molecular
arrangement from a red one. But there are some physical peculiarities
which also influence heat radiation, quite independently of this
_surface_ condition. If we take pieces of red, black, green, and yellow
glass, and expose them when the dew is condensing, we shall find that
moisture will show itself first on the yellow, then on the green glass,
and last of all upon the black or red glasses. The same thing takes
place if we expose  fluids in white glass bottles or troughs,
in which case the surfaces are all alike. If against a sheet of
glass, upon which moisture has been slightly frozen, we place glasses
similarly  to those already described, it will be found that
the earliest heat-rays will so warm the red and the black glasses, that
the ice will be melted opposite to them, long before any change will be
seen upon the frozen film covered by the other colours.

The order in which heat permeates  media, it has already been
shown, very nearly agrees with their powers of radiation.

These most curious results have engaged the attention of Melloni,
to whose investigations we owe so much; and from the peculiar order
of radiations, which present phenomena of an analogous character to
those of the  rays of light, obtained by him from dissimilarly
 bodies, he has been led to imagine the existence of a
“heat-colouration.” That is, the heat-rays are supposed to possess
properties like luminous colour although invisible; and, consequently,
that a blue surface has a strong affinity for the blue heat-rays,
a red surface for the red ones, and so on through the scale. The
ingenuity of this hypothesis has procured it much attention; but now,
when the Newtonian hypothesis of the refrangibility of light is nearly
overturned, we must not, upon mere analogy, rush to the conclusion
that the rays of heat have different orders of refrangibility, which
Melloni’s hypothesis requires.[58]

Can anything be more calculated to impress the mind with the
consciousness of the high perfection of natural phenomena, than the
fact, that the colour of a body should powerfully influence the
transmission of a principle which is diffused through all nature,
and also determine the rate with which it is to pass off from its
surface. Some recent experiments have brought us acquainted with other
facts connected with these heat-radiations, and the power of heat,
as influenced by the calorific rays, to produce molecular changes in
bodies, which bear most importantly on our subject.

If we throw upon a plate of polished metal a prismatic spectrum
(deprived, as nearly as possible, of its chemical power, by being
passed through a deep yellow solution--which possesses this property
in a very remarkable manner, as will be explained when we come to the
examination of the chemical action of the sun’s rays)--it will be
found, if we afterwards expose the plate to the action of vapour, very
slowly raised from mercury, that the space occupied by the red rays,
and those which lie without the spectrum below it, will condense the
vapour thickly, while the portion corresponding with the other rays
will be left untouched. This affords us evidence of the power of solar
heat to produce, very readily, a change in the molecular structure of
solid bodies. If we allow the sun’s rays to permeate  glasses,
and then fall upon a polished metallic surface, the result, on exposing
the plate to vapourisation, will be similar to that just described.
Under yellow and green glasses no vapour will be condensed; but on the
space on which the rays permeating a red glass, or even a blackened
one, fall, a very copious deposit of vapour will mark with distinctness
the spaces these glasses covered. More remarkable still, if these or
any other  bodies are placed in a box, and a polished metal
plate is suspended a few lines above them, the whole being kept _in
perfect darkness_ for a few hours, precisely the same effect takes
place as when the arrangement is exposed to the full rays of the sun.
Here we have evidence of the radiating heat of bodies, producing even
in darkness the same phenomena as the transmitted heat-rays of the sun.
We must, however, return to the examination of some of these and other
analogous influences under the head of actino-chemistry.

From these curious discoveries of inductive research we learn some high
truths. Associated with light--obeying many of the same laws--moving
in a similar manner--we receive a power which is essential to the
constitution of our planet. This power is often manifested in such
intimate combination with the luminous principle of the solar rays,
that it has been suspected to be but another form of the same agency.
While, however, we are enabled to show the phenomena of one without
producing those which distinguish the other, we are constrained to
regard heat as something dissimilar to light. It is true that we
appear to be tending towards some point of proof on this problem; but
we are not in a position to declare them to be forms of one common
power, or “particular solutions of one great physical equation.”[59]
In many instances it would certainly appear that one of these forces
was directly necessary to the production of the other; but we have also
numerous examples in which they do not stand in any such correlation.

We learn, from the scientific facts which we have been discussing, a
few of the secrets of natural magic. In their relations to heat, every
flower, which adds to the adornment of the wilds of nature or the
carefully-tended garden of the florist, possesses a power peculiar to
itself;

    “Naiad-like lily of the vale,”

and,

    “---- The pied wind-flowers, and the tulip tall,
    And narcissi, the fairest among them all,”

are, by their different colours, prevented from ever having the same
temperatures under the same sunshine.

Every plant bears within itself the measure of the heat which is
necessary for its well-being, and is endued with functions which mutely
determine the relative amount of dew which shall wet its 
leaves. Some of the terrestrial phenomena of this remarkable principle
will still further illustrate the title of this volume.

To commence with the most familiar illustrations, let us consider the
consequences of change of temperature. However slight the additional
heat may be to which a body is subjected, it expands under its
influence; consequently, every atom which goes to form the mass of
the earth moves under the excitation, and the first heat ray of the
morning which touches the earth’s surface, sets up a vibration which
is continued as a tremor to its very centre. The differences between
the temperature of day and night are considerable; therefore all bodies
expand under the influence of the higher, and contract under that of
the lower temperature. During the day, any cloud obscuring the sun
produces, in every solid, fluid, or aëriform body, within the range
of solar influence, a check: the particles which had been expanding
under the force of heat suddenly contract. Thus there must of necessity
be, during the hours of sunshine, a tendency in all bodies to dilate,
and during the hours of night they must be resuming their original
conditions.

Not only do dissimilar bodies radiate heat in different degrees, but
they conduct it also with constantly varying rates. Heat passes along
silver or copper with readiness, compared to its progress through
platinum. It is conducted by glass but slowly, and still more slowly
by wood and charcoal. We receive some important intimations of the
molecular structure of matter, from those experiments which prove that
heat is conducted more readily along some lines than others. In some
planes, wood and other substances are better conductors than in others.
The metallic oxides or earths are bad conductors of heat, by which
provision the caloric absorbed by the sun’s rays is not carried away
from the surface of this planet so rapidly as it would have been had
it been of metal, but is retained in the superficial crust to produce
the due temperature for healthful germination and vegetable growth. The
wool and hair of animals are still inferior conductors, and thus, under
changes of climate and of seasons, the beasts of the field are secured
against those violent transitions from heat to cold which would be
fatal to them. Hair is a better conductor than wool: hence, by nature’s
alchemy, hair changed into wool in the animals of some countries on the
approach of winter, and feathers into down.

It is therefore evident that the rate at which solar heat is conducted
into the crust of the earth must alter with the condition of the
surface upon which it falls. The conducting power of all the rocks
which have been examined is found to vary in some degree.[60]

It follows, as a natural consequence of the position of the sun to
the earth, that the parts near the equator become more heated than
those remote from it. As this heat is conducted into the interior of
the mass, it has a tendency to move to the colder portions of it, and
thus the heat absorbed at the equator flows towards the poles, and
from these parts is carried off by the atmosphere, or radiated into
space. Owing to this, there is a certain depth beneath the surface of
our globe at which an equal temperature prevails, the depth increasing
as we travel north or south from the equator, and conforming to the
contour of the earth’s surface, the line sinking under the valleys and
rising under the hills.[61]

A question of great interest, in a scientific point of view, is the
temperature of the centre of the earth. We are, of course, without the
means of solving this problem; but we advance a little way onwards
in the inquiry by a careful examination of subterranean temperature
at such depths as the enterprise of man enables us to reach. These
researches show us, that where the mean temperature of the climate
is 50°, the temperature of the rock at 59 fathoms from the surface
is 60°; at 132 fathoms it is 70°; at 239 fathoms it is 80°: being an
increase of 10° at 59 fathoms deep, or 1° in 35·4 feet; of 10° more at
73 fathoms deeper, or 1° in 43·8 feet; and of 10° more at 114 fathoms
still deeper, or 1° in 64·2 feet.[62]

Although this would indicate an increase to a certain depth of about
one degree in every fifty feet, yet it would appear that the rate of
increase diminishes with the depth. It appears therefore probable, that
the heat of the earth, so far as man can examine it, is due to the
absorption of the solar rays by the surface. The evidences of intense
igneous action at a great depth cannot be denied, but the doctrine of
a cooling mass, and of the existence of an incandescent mass, at the
earth’s centre, remains but one of those guesses which active minds
delight in. The mean annual temperature of this planet is subject to
variations, which are probably dependent upon some physical changes in
the sun himself, or in the atmospheric envelope by which that orb is
surrounded. The variations over the earth’s surface are great. At the
equator we may regard the temperature as uniformly existing at 80°,
while at the poles it is below the freezing point of water; and as far
as observations have been made, the subterranean temperatures bear a
close relation to the thermic condition of the climate of the surface.
The circulation of water through faults or fissures in the strata is,
without doubt, one means of carrying heat downwards much quicker than
it would be conducted by the rocks themselves. It is not, however,
found that the quantity of water increases with the depth. In the mines
of Cornwall, unless where the ground is very loose, miners find that,
after about 150 fathoms (900 feet), the quantity of water rapidly
diminishes. That water must ascend from very much greater depths is
certain, from the high temperatures at which many springs flow out at
the surface. In the United Mines in Cornwall, water rises from one part
of the lode at 90°; and one of the levels in these workings is so hot
that, notwithstanding a stream of cold water is purposely brought into
it to reduce the temperature, the miners work nearly naked, and will
bathe in water at 80° to cool themselves. At the bottom of Tresavean
Mine, in the same county, about 320 fathoms from the surface, the
temperature is 100°.

One cause of the great heat of many of our deep mines, which appears
to have been entirely lost sight of, is the chemical action going
on upon large masses of pyritic matter in their vicinity. The heat,
which is so oppressive in the United Mines, is, without doubt, due to
the decomposition of immense quantities of the sulphurets of iron and
copper known to be in this condition at a short distance from these
mineral works.

The heat which man is enabled to measure beneath the earth’s surface,
appears to be alone due to the conducting powers of the rocks
themselves; it has been observed that the line of equal temperature
follows, as nearly as possible, the elevations and depressions which
prevail upon the surface, and the diminishing rate of increase beyond
this line, certainly is such as would arise, was all the heat so
measured, the result of the passage of the heat by conduction through
the crust of rocks.

Whether or not the subterranean bands of equal heat have any strict
relation, upon a large scale, to the isothermic lines which have been
traced around most portions of our globe, is a point which has not yet
been so satisfactorily determined as to admit of any general deductions.

The Oriental story-teller makes the inner world a place of rare
beauty--a cavern temple, bestudded with self-luminous gems, in which
reside the spiritual beings to whom the direction of the inorganic
world is confided.

The Philosopher, in the height of his knowledge, has had dreams as
absurd as this; and amid the romances of science, there are not to be
found any more strange visions than those which relate to the centre
of our globe. At the same time it must be admitted, that many of the
peculiar phenomena which modern geological researches have brought to
light, are best explained on the hypothesis of a cooling sphere, which
necessarily involves the existence of a very high temperature towards
the centre.

We have already noticed some remarkable differences between solar and
terrestrial heat; but a class of observations by Delaroche[63] still
requires our attention. Solar heat passes freely through colourless
glass, whereas the radiations from a bright fire or a mass of
incandescent metal are entirely obstructed by this medium. If we place
a lamp or a ball of glowing hot metal before a metallic reflector, the
focus of accumulated heat is soon discovered; but if a glass mirror
be used, the light is reflected, but not the heat; whereas, with the
solar rays, but little difference is detected, whether vitreous or
metallic reflectors are employed. It is well known that glass lenses
refract both the light and heat of the sun, and they are commonly known
as burning-glasses: the heat accumulated at their focal point being
of the highest intensity. If, instead of the solar beam, we employ,
in our experiments, an intense heat produced by artificial means,
the passage of it is obstructed, and the most delicate thermometers
remain undisturbed in the focus of the lens. Glass exposed in front
of a fire becomes warm, and by conduction the heat passes through it,
and a secondary radiation takes place from the opposite side.[64] It
has been found that glass is transcalescent, or _diathermic_, to some
rays of terrestrial heat, and _adiathemic_, or opaque for heat, to
others[65]--that the capability of permeating glass increases with the
temperature of the ignited body--and that rays which have passed one
screen traverse a second more readily. It would, however, appear that
something more than a mere elevation of temperature is necessary to
give terrestrial heat-radiations the power of passing through glass
screens, or, in other words, to acquire the properties of solar heat.

To give an example. The heat of the oxy-hydrogen flame is most intense,
yet glass obstructs it, although it may be assisted by a parabolic
reflector. If this flame is made to play upon a ball of lime, by which
a most intense light is produced, the heat, which has not been actually
increased, acquires the power of being refracted by a glass lens, and
combustible bodies may be ignited in its focus.

It certainly appears from these results, that the undulatory hypothesis
holds true, so far as the motion of the calorific power is concerned.
At a certain rate the vibrations are thrown back or stopped by the
opposing body, while in a state of higher excitation, moving with
increased rapidity, they permeate the screen.[66] This does not,
indeed, interfere with the refined theory of Prévost,[67] which
supposes a mutual and equal interchange of caloric between all bodies.

The most general effect of heat is the expansion of matter; solids,
liquids, and airs, all expand under its influence. If a bar of metal
is exposed to calorific action, it increases in size, owing to its
particles being separated farther from each other: by continuing this
influence, after a certain time the cohesion of the mass is so reduced
that it melts, or becomes liquid, and, under the force of a still
higher temperature, this molten metal may be dissipated in vapour. It
would appear as if, under the agency of the heat applied to a body, its
atoms expanded, until at last, owing to the tenuity of the outer layer
or envelope of each atom, they were enabled to move freely over each
other, or to interpenetrate without difficulty. That heat does really
occasion a considerable disturbance in the corpuscular arrangement
of bodies, may be proved by a very interesting experiment. A bar of
heated metal is placed to cool, with one end supported upon a wedge
or a ring of a different metal the other resting on the ground. In
cooling, a distinct musical sound is given out, owing to the vibratory
action set up among the particles of matter moving as the temperature
declines.[68]

Heat is diffused through all bodies in nature, and, as we shall
presently see, may be developed in many different ways. We may,
therefore, infer, that in converting a sphere of ice into water, and
that again into steam, we have done nothing more than interpenetrate
the mass with a larger quantity of heat, by which its atoms are more
widely separated, and that thus its molecules become free to move
about each other. Hence, from a solid state, the water becomes fluid;
and then, if the expansive force is continued, an invisible vapour.
If these limits are passed by the powers of any greatly increased
thermic action, the natural consequence, it must be seen, will be the
separation of the atoms from each other, to such an extent that the
molecule is destroyed, and chemical decomposition takes place.

By the agency of the electricity of the voltaic battery, we are enabled
to produce the most intense heat with which we are acquainted, and by a
peculiarly ingenious arrangement Mr. Grove has succeeded in resolving
water by the mere action of heat into its constituent elements--oxygen
and hydrogen gases. That this decomposition is not due to the voltaic
current, but to the heat produced by it, was subsequently proved by
employing platina heated by the oxy-hydrogen flame.[69]

This interesting question has been examined with great care by Dr.
Robinson of Armagh, who has shown that, as the temperature of water is
increased, the affinity of its elements is lessened, until at a certain
point it is eventually destroyed. This new and startling fact appears
scarcely consistent with our knowledge that a body heated so as to
be luminous has the power of causing the combination of the elements
of water with explosive violence.[70] But as this acute experimental
philosopher somewhat boldly but still most reasonably inquires: “Is
it not probable that, if not light, some other actinic power (like
that which accompanies light in the spectrum, and is revealed to us
by its chemical effects in the processes of photography) is evolved
by the heat, and, though invisible, determines, in conjunction with
the affinity, that atomic change which transforms the three volumes of
oxygen and hydrogen into two of steam?”[71]

This speculation explains, in a very satisfactory manner, some
results which were obtained by Count Rumford, in 1798. In a series of
experiments instituted for the purpose of examining “those chemical
properties of light which have been attributed to it,” he has shown
that many cases of chemical decomposition occur in perfect darkness,
under the influence of heat, which are precisely similar to those
produced by exposure to the sun’s rays.[72]

It must, however, be remembered, that both solar light and heat are
sometimes found in direct antagonism to actinic power, and that the
most decided chemical changes are produced by those rays in which
neither heat nor light can be detected. The most remarkable phenomena
of this class will be explained under the head of actinism.

One of the most curious relations which as yet have been discovered
between light and heat is, that, the temperature at which all bodies
become incandescent, excepting such as are phosphorescent, is uniform.
The point on the thermometer (Fahrenheit’s scale) when the eye by
perfect repose is enabled to detect the first luminous influence, may
probably be regarded as, or very near, 1000°. Daniel has fixed this
point at 980°, Wedgwood at 947°, and Draper at 977°.[73] Dr. Robinson
and Dr. Draper, by independent observations, have both arrived at the
conclusion, that the first gleam of light which appears from heated
platina is not red, but of a lavender gray, the same in character of
colour as that detected by Sir John Herschel among the most refrangible
rays of the solar spectrum.[74]

It must be admitted, that the question of the identity, or otherwise,
of light and radiant heat, is beset with difficulties. Many of their
phenomena are very similar--many of their modes of action are alike:
they are often found as allied agencies; but they as frequently exhibit
extreme diversity of action, and they may be separated from each other.

We have now examined the physical conditions and properties of this
most important element, and we must proceed to learn something of the
means by which it may be developed, independently of its solar source.

This extraordinary principle exists in a latent state in all bodies,
and may be pressed out of them. The blacksmith hammers a nail until it
becomes red hot, and from it he lights the match with which he kindles
the fire of his forge. The iron has by this process become more dense,
and percussion will not again produce incandescence until the bar has
been exposed in fire to a red heat. The only inference we can draw
from this result is, that by hammering the particles have been driven
closer together, and the heat driven out; now further hammering will
not force the atoms nearer, and consequently no additional quantity of
heat can be developed; the iron is made hot in a fire, it absorbs heat,
the particles are restored to their former state, and we can now again
by hammering develope both heat and light. The Indian produces a spark
by the attrition of two pieces of wood. By friction, two pieces of ice
may be made to melt each other; and could we, by mechanical pressure,
force water into a solid state, an immense quantity of heat would be
set free. By the condensation of hydrogen and oxygen gases, pulverulent
platinum will become glowing red-hot, and, with certain precautions,
even the compact metal, platinum, itself; the heat being derived from
the gases, the union of which it has effected. A body passing from the
solid to the fluid state absorbs heat from all surrounding substances,
and hence a degree of cold is produced. The heat which is thus removed
is not destroyed--it is held combined with the fluid; it exists in a
latent state. Fluids, in passing into a gaseous form, also rob all
surrounding bodies of an amount of heat necessary to maintain the
aëriform condition. From the air or from the fluid, this heat may,
as we have shown above, be again extracted. Locked in a pint measure
of air, there exists sufficient heat to raise several square inches
of metal to glowing redness. By the compression of atmospheric air
this may be shown, and with a small condensing syringe a sufficient
quantity of heat may be set free to fire the _Boletus igniarius_,
which, impregnated with nitre, is known as _amadou_. We are acquainted
with various sources from which heat may be developed for artificial
purposes: the flint-and-steel is an example of the production of heat
by mechanical force, and the modern lucifer-match, of the combined
action of friction and chemical affinity. These of themselves would
admit of a lengthened discourse; but it is necessary that we carefully
examine some of the less familiar phenomena of heat under the
influences of changes of chemical condition.

If spirits of wine and water are mixed together, a considerable degree
of heat is given out, and by mixing sulphuric acid and water, an
infinitely larger quantity. If sulphuric acid (oil of vitriol) and
spirit of wine, or nitric acid (aquafortis) and spirits of turpentine,
at common temperatures, be suddenly mixed, so much heat is set free
as to ignite the spirit. In each of these instances there is a
condensation of the fluid. In nearly all cases of solution, cold is
produced by the absorption of the heat necessary to sustain the salt
in a liquid form; but when potash dissolves in water, heat is given
out, which is a fact we cannot yet explain. If potassium is placed on
water, it seizes the oxygen of the water and sets fire to the hydrogen
gas liberated by the heat produced in the change of form. Antimony
and many other metals thrown into chlorine gas ignite and burn with
brilliancy: the same phenomenon takes place in the vapours of iodine or
bromine. Many chemical combinations, as the chloride of potassium and
sulphur explode with a blow; whilst the slightest friction occasions
the detonation of the fulminating salts of silver, mercury, and
gold. Compounds of nitrogen and chlorine, or iodine, are still more
delicately combined--the former exploding with fearful violence on
the contact of any oleaginous body, and the latter by the smallest
elevation of temperature: both of them destroying the vessels in which
they may be contained.

Gun cotton presents some peculiar phenomena which may merit brief
attention. This peculiar compound is prepared by the action of nitric
acid on cotton fibre. The general appearance of the cotton is not
altered, but a remarkable physical change has taken place. It is
now soluble in ether, and forms a gelatinous compound:--it explodes
violently at a temperature which is insufficient for the combustion
of gunpowder. Indeed, from, as it would appear, slight electrical
disturbances taking place in the gun cotton itself, it not unfrequently
explodes spontaneously. These fearful disturbances of the forces
which hold bodies in combination are explained with difficulty. May
it not be, that an enormous quantity of the calorific and chemical
principles is held in a state of extreme tension around the particles
of the compound, and that the equilibrium being destroyed, the whole is
developed in destructive rapidity?

The fact of great heat being evolved during the conversion of a body
from a solid to a gaseous state, as in the explosion of gunpowder or
gun cotton, which is a striking exception to the law of latent heat, as
it prevails in most cases, admits of no more satisfactory explanation.

As mechanical force produces calorific excitation, so we find that
every movement of sap in vegetables, and of the blood and fluids in
the animal economy, causes a sensible increase of heat. The chemical
processes constantly going on in plants and animals are another source
of heat, in addition to which nervous energy and muscular movement must
be regarded as producing the caloric which is essential to the health
and life of the latter. Digestion has been considered as a process
of combustion; and the action between the elements of food, and the
oxygen conveyed by the circulation of the blood to every part of the
body, regarded as the source of animal heat; and, without doubt, it
is one great source, although it can scarcely be regarded as the only
one.[75]

The _vis vitæ_, or vital power, influences the delicate and beautiful
system of nerves; and as life (an essence of the rarest and most
subtile order, a diffusive influence) runs through them, from the brain
to the extremities of the members of the body, it sets those tender
threads in rapid vibration, and heat is developed. By this action,
the circulation of the blood is effected; the muscle is maintained
in an elastic condition, ready to perform the tasks of the will; and
through these agencies is the warm and fluid blood fitted to receive
its chemical restoratives in the lungs, and the stomach to support
changes for which it is designed--chemical also--by which more heat
is liberated. Was digestion--_Eremacausis_, as the slow combustion
produced by combination with oxygen is called--the only source of
animal heat, why should the injury of one filmy nerve place a member of
the body for ever in the condition of stony coldness? Or why, chemical
action being most actively continued after a violent death, by the
action of the gastric juices upon the animal tissues, should not animal
heat be maintained for a much longer period than it is found to be
after respiration has ceased?[76]

In studying the influences of caloric upon the conditions of matter,
we must regard the effects of extreme heat, and also of the greatest
degrees of cold which have been obtained.

There are a set of experiments by the Baron Cagniard de la Tour, which
appear to have a very important bearing on some conditions that may
be supposed to prevail in nature, particularly if we adopt the view of
a constantly increasing temperature towards the centre of our earth.
If water, alcohol, or ether, is put into a strong glass tube of small
bore, the ends hermetically sealed, and the whole exposed to a strong
heat, the fluid disappears, being converted into a transparent gas;
but, upon cooling, it is again condensed, without loss, into its
original fluid state.[77] In this experiment, fluid bodies have been
converted into elastic transparent gases with but small change of
volume, under the pressure of their own atmospheres. We can readily
conceive a similar result occurring upon a far more extensive scale.
In volcanic districts, at great depths, and consequently under the
pressure of the superincumbent mass, the siliceous rocks, or even
metals, may, from the action of intense heat, be brought into a fluid,
or even a gaseous condition, without any change of volume, since
the elastic force of heat is opposed by the rigid resistance of the
pressure of the surrounding rocks. Some beautiful experiments by Mr.
Hopkins, of Cambridge, have proved that the temperature necessary to
melt a body must be considerably elevated as the mechanical pressure to
which it is subjected is increased.

Directly connected with the results of Cagniard de la Tour are a yet
more remarkable set of phenomena, which have been investigated by
M. Boutigny,[78] and generally known as the “spheroidal condition”
of bodies. If water is projected upon very hot metal it instantly
assumes a spheroidal form--an internal motion of its particles may
be observed--it revolves with rapidity, and evaporates very slowly.
If a silver or platinum capsule, when brought to a bright red heat,
is filled with cold water, the whole mass assumes the spheroidal
state, the temperature of the fluid remaining considerably below the
boiling point, so long as the red heat is maintained. If we allow the
vessel to cool below redness in the dark, the water then bursts into
active ebullition, and is dissipated into vapour with almost explosive
violence. An equal quantity of water being projected into two similar
vessels, over the fire, one cold and the other red hot, it will be
found that the water in the cold vessel will boil and evaporate long
before that in the one which is red hot.

Another form of this experiment is exceedingly instructive. If a mass
of white hot metal is suddenly plunged into a vessel of cold water, the
incandescence is not quenched, the metal shines with a bright white
light, and the water is seen to circulate around, but at some distance
from the glowing mass, being actually repelled by calorific agency. At
length, when the metal cools, the water comes in contact with it, and
boils with energy.

A result similar to this was observed by Perkins, but its correctness
most unjustly doubted. Having made an iron shell containing water, and
carefully plugged up, white hot, it was found that the steam never
exerted sufficient force to burst the vessel, as it was expected
it would do. He caused a hole to be drilled into the bottom of the
white-hot shell, and he was surprised to find that no water flowed
through the orifice, until the iron was considerably cooled, when it
issued forth with violence in the form of steam. Here we have the
_Cagniard de la Tour state_ first induced, and the calorific repulsion
of the spheroidal state supervenes. If water is poured upon an iron
sieve, the wires of which are made red hot, it will not percolate;
but on cooling, it runs through rapidly. M. Boutigny, pursuing this
curious inquiry, has recently proved that the moisture upon the skin
is sufficient to protect it from disorganization, if the arm is plunged
into baths of melted metal. The resistance of the surfaces is so great,
that little elevation of temperature is experienced.[79] Professor
Plücker, of Bonn, has stated that by washing the arm with ether
previously to plunging it into melted metal, the sensation produced,
while in the molten mass, is that of freezing coldness.

We have now seen that heat at different degrees of intensity appears
to produce chemical composition--that it decomposes combined
elements--that it alters the conditions of bodies, and actually
maintains so powerfully a repellent force, that fluids cannot touch the
heated body. More than this, it exerts a most powerful antagonistic
influence over all chemical relations. If, to give one example,
the volatile element iodine is put into a glowing hot capsule, it
resolves itself immediately into a spheroid. Potash rapidly combines
with iodine; but if a piece of this alkali is thrown upon it in
the capsule, it also takes the spheroidal form, and both bodies
revolve independently of each other, their chemical affinities being
entirely suspended;--but allow the capsule to cool, and they combine
immediately. Science teaches us that a temperature so exalted as not to
burn organic bodies may be produced, and points to us this remarkable
fact, that the destructive limits of heat are measured between certain
degrees--beyond which a fire, by reason of its intensity, ceases to
develope heat. What is the radiant force into which this principle
changes?

The experiments of Cagniard de la Tour and of Boutigny (d’Evreux),
connect themselves, in a striking manner, with those of Mr. Grove and
Dr. Robinson; and they teach us that but a very slight alteration in
the proportions of the calorific principle given to this planet would
completely change the character of every material substance of which it
is composed, unless there was an alteration in the physical condition
of the elements themselves.

Supposing the ordeal of fiery purification to take place upon this
earth, these experiments appear to indicate the mighty changes which
would thence result. There would be no annihilation, but everything
would be transformed from the centre of the globe to the verge of its
atmosphere--old things would pass away, all things become new, and the
beautiful mythos of the phœnix be realized in the fresh creation.

The deductions to be drawn from the results obtained by abstracting
heat from bodies are equally instructive. By taking advantage of the
cooling produced by the rapid solution of salts of several kinds in
water, an intense degree of coldness may be produced.[80] Indeed, the
absorption of heat by liquefaction may be shown by the use of metallic
bodies alone. If lead, tin, and bismuth, are melted together, and
reduced to a coarse powder by being poured into water, and the alloy
then dissolved in a large quantity of quicksilver, the thermometer will
sink nearly 50 degrees. An intense amount of cold will result from
the mixture of muriate of lime and snow, by which a temperature of
50° below the zero of Fahrenheit, or 82° below the freezing point of
water, is produced. By such a freezing mixture as this, mercury will
be rendered solid. A degree of cold, however, far exceeding it, has
lately been obtained by the use of solid carbonic acid and ether.[81]
Solid carbonic acid is itself procured from the gas liquefied by
pressure; which liquid, when allowed to escape into the air, evaporates
so rapidly that a large quantity of it is congealed by being robbed of
its combined heat by the vaporizing portion. When this solid acid is
united with ether, a bath is formed in which the carbonic acid will
remain solid for twenty or thirty minutes. By a mixture of this kind,
placed under the receiver of an air-pump, a good exhaustion being
sustained, a degree of cold 166° below zero is secured. By this intense
cold, many of the bodies which have hitherto been known to us only in
the gaseous state have been condensed into liquids and solids. Olefiant
gas, a compound of hydrogen and carbon, was brought into a liquid
form. Hydriodic and hydrobromic acids could be condensed into either a
liquid or a solid form. Phosphuretted hydrogen, a gas which inflames
spontaneously when brought into contact with the air or with oxygen,
became a transparent liquid at this great reduction of temperature.
Sulphurous acid may be condensed, by pressure and a reduction of
temperature, into a liquid which boils at 14° Fahrenheit, but by the
carbonic acid bath it is converted into a solid body, transparent and
without colour. Sulphuretted hydrogen gas solidifies at 122° below
zero, and forms a white substance resembling a mass of crystals of
sea-salt.

A combination of the two gases, chlorine and oxygen, becomes solid at
-75°, and the protoxide of nitrogen at -150°. Cyanogen, a compound
of carbon and nitrogen--the base of prussic acid--is solidified at
30° below the zero of our thermometric scale. The well-known pungent
compound, ammonia, so exceedingly volatile at common temperatures,
is converted into a crystalline, translucent, white substance at the
temperature of -103°. The difficulties which necessarily attend the
exposure of a body to extreme cold and great pressure at the same time,
appear to be the only obstacle to the condensation of oxygen, hydrogen,
and nitrogen gases. A sufficient amount of condensation was, however,
effected by Dr. Faraday, to lead him to the conclusion, arrived at
also by other evidences, that hydrogen, the lightest of the ponderable
bodies, partakes of the nature of a metal.[82]

During the solidification of water by freezing, some remarkable facts
may be noticed.

Water, in cooling, gradually condenses in volume until it arrives at
40° Fahr., which appears to be the point of greatest density. From this
temperature to that of 32°, the point at which it begins to solidify,
its volume remains unchanged,[82] as crystallisation (freezing) begins,
the bulk increases, the mass becomes specifically lighter, and it swims
on the surface of the fluid. From 40° to 32° the particles of water
must be taking up that new position which is essential to the formation
of the solid--ice; and while this is taking place, every substance held
in solution by the water is rejected.

If we mix with water the deepest colouring matter--the strongest acid
or the most acrid poison--they are each and all rejected during the
process of freezing, and if the water has been kept in a state of
agitation during the process--so that the liberated particles may not
be mechanically entangled--the ice will be transparent, colourless,
tasteless, and inert--the substances rejected being gathered together
in the centre of the frozen mass in a state of intense concentration.
In like manner, even the atmospheric air, which is always held in
solution, is rejected, and hence the reason why all the ice which
forms upon still ponds is full of air-bubbles, while the ice which is
produced in agitated water is perfectly free from them. This in itself
is a remarkable condition, the entire bearing of which is not clearly
understood; but a still more singular fact has been discovered in
intimate connection with the rejection of all matter from a freezing
solution. Water, which in this way is freed entirely of air, will not
boil at 212° F., the ordinary boiling point of water.

If a mass of ice formed in the manner described is placed in a vessel,
and being just covered with a film of oil, to prevent the absorption of
air, is melted over a lamp or fire, and the heat continued, it will,
so far from being converted into steam at 212°, continue to increase
in temperature up to 270° or more, and then burst into ebullition with
such explosive violence as to rend the vessel in which it is confined.

From this experiment we learn that did water exist in any other
condition than that in which we find it--even with the apparently
simple difference of containing no air--it would not be safe to employ
it in any culinary or manufacturing operation, since its use would be
followed by explosions as dangerous as those of gunpowder.

Such researches as these prove to us the admirable adaptation of all
things to their especial ends--the beautiful adjustment of the balance
of forces throughout creation.

The refinements of Grecian philosophy saw, without the aids of
inductive science, that the outward vesture of nature covered a host
of mysterious agencies to which its characteristics were directly
due. In their dream of the four elements, fire, the external and
visible form of heat, was regarded as the cause of vitality, and the
disposer of every organised and unorganised condition of matter. Their
idealisations have assumed another form, but the researches of modern
science have only established their universality and truth.

The great agents at work in nature--the mighty spirits bound to
never-ending tasks, which they pursue with unremitting toil, are of so
refined a character, that they will probably remain for ever unknown
to us. The arch-evocator, with the wand of induction, calls; but the
only answer to his evocation is the manifestation of power in startling
effects. Science pursues her inquiries with zeal and care: she tries
and tortures nature to compel her to reveal her secrets. Bounds are,
however, set to the powers of mortal search: we may not yet have
reached the limits within which we are free to exercise our mental
strength; but, those limits reached, we shall find an infinite region
beyond us, into which even conjecture wanders eyeless and aimless, as
the blind Cyclops groping in his melancholy cave.[83]

All we know of heat is, that striking effects are produced which we
measure by sensation, and by instruments upon which we have observed
that given results will be produced under certain conditions: of
anything approaching to the cause of these we are totally ignorant.
The wonder-working mover of some of the grandest phenomena in
nature--giving health to the organic world, and form to the inorganic
mass--producing genial gales and dire tornadoes--earthquake strugglings
and volcanic eruptions--ministering to our comforts in the homely fire,
and to advancement in civilisation in the mighty furnace, and the
ingenious engine which drains our mines, or traverses our country with
bird-like speed,--will, in all probability, remain for ever unknown to
man. The immortal Newton, many of whose guesses have a prophetic value,
thus expresses himself:--“Heat consists in a minute vibratory motion in
the particles of bodies, and this motion is communicated through an
apparent vacuum by the undulations of a very subtile elastic medium,
which is also concerned in the phenomena of light.”

Our experimental labours and our mathematical investigations have
considerably advanced our knowledge since the time of Newton; yet still
each theory of heat strangely resembles the mystic lamp which the
Rosicrucian regarded as a type of eternal life--a dim and flickering
symbol, in the tongue-like flame of which imagination, like a child,
can conjure many shapes.

Modern theory regards heat as a manifestation of motion, and experiment
proves that a body falling through a certain space generates a definite
quantity of heat, while observation shows that the waters at the base
of the Falls of Niagara possess a temperature 1° higher than when they
first glide over the edge of the precipice.

This increase of temperature is due to the mechanical force due to
the fall, and is no more an evidence of the conversion of motion into
heat, than is the old experiment of rubbing a button until it becomes
hot. At all events, the fact that a given amount of mechanical force
always produces an equivalent of heat is as applicable to the idea of
a “subtile elastic medium” which is diffused through all matter, as to
the, at present, favourite hypothesis.

So far has this view been strained, that the temperature of the planets
has been referred to their motions, and speculation has aided the
mathematician in determining the cessation of planetary motion, by
the conversion of it into heat. It is true that other theorists have
supposed points in space upon which this heat might be concentrated and
reflected back again to produce motion.

There may be much of the poetic element in such speculations, but it is
of that order which belongs rather to the romantic than to the real.

A speculation which has more of truth, and which is, indeed,
demonstrable, cannot fail to impress every mind with its beauty, and
probable correctness.

In the growth of a tree, its wood and all its products are the result
of certain external forces effecting chemical changes. Carbonic acid
is decomposed, the carbon is retained, and oxygen given off, and
assimilations of a complex character are in constant progress to
produce the various compounds of oxygen, hydrogen, nitrogen, and carbon.

Every condition of organised forms is due to the external excitation
of light and heat, and in the chemical changes which take place, an
equivalent of these principles, or powers--it signifies but little
according to which view we may regard them--is absorbed, and retained
as essential to the condition of the matter formed. Let us confine
our attention to wood--although the position applies equally to every
organic product. A cubic foot of wood is formed by the decomposition
of a certain quantity of carbonic acid, by the vital function of the
plant, excited by the solar rays, which are involved in the mass which
nature by “her wondrous alchemy” has made. Eventually this cubic foot
of wood is subjected to a process of chemical change--combustion; by
the application of a single spark,--and in the disintegration of the
wood, its carbon combining with oxygen to form carbonic acid, its
hydrogen to form water, which is returned to the air, a large amount of
light and heat is produced. This is exactly equivalent to the amount
which was engaged in its formation. Indeed, the sunshine which fell
upon the leaves of the forest tree, of which the log formed a part, has
been hoarded up, and we again develope it in its original state of heat
and light.

The vast coal beds of England were formed by the rapid growth and quick
decay of a peculiar class of plants under the influence of a tropical
sun. They have been buried myriads of ages, under hundreds of feet of
sandy rock. By the industry of the miner the coal is brought again
to the surface, and we develope from it those powers by which it was
formed.

In the fire which gives comfort to our homes--in the furnace which
generates force for the purposes of manufacture, or to propel the
railway engine and its ponderous train--in the gas with which we
illumine our streets and gladden during the long winter nights our
apartments, we are developing that heat and light which fell upon
the earth with all its quickening influences millions of ages before
yet the Creator had called into existence the monarch Man, for whose
necessities these wondrous formations were designed.


FOOTNOTES:

[43] The following table of the rays penetrating  glass has
been given by Melloni, in his memoir _On the Free Transmission of
Radiant Heat through Different Bodies_:--

    Deep violet               53
    Yellowish red (flaked)    53
    Purple red (flaked)       51
    Vivid red                 47
    Pale violet               45
    Orange red                44
    Clear blue                42
    Deep yellow               40
    Bright yellow             34
    Golden yellow             33
    Deep blue                 33
    Apple green               26
    Mineral green             23
    Very deep blue            19

Translated in the Scientific Memoirs, vol. i. p. 30.

[44] “The physical characters of this species of glass, which acts
so differently from the other species of  glass in all the
phenomena of calorific absorption, are, 1st, its intercepting almost
totally the rays which pass through alum; 2nd, its entirely absorbing
the red rays of the solar spectrum. I have already stated that their
colouration is produced almost entirely by the oxide of copper.

“Thus, the colouring matters of the  glasses, while they
so powerfully affect the relations of quantity which the different
rays of ordinary light bear to each other, exercise no elective
action on the concomitant calorific rays. This curious phenomenon is
the more remarkable as the colouring matters absorb almost always
a very considerable portion of the heat _naturally transmitted by
the glass_. The following are, in fact, the calorific transmissions
of the seven  glasses referred to; the transmission of the
common glass being represented by 100; red glass, 82·5; orange, 72·5;
yellow, 55; bluish-green, 57·5; blue, 52·5; indigo, 30; violet, 85.
The quantity of heat absorbed through the action of the colouring
substances is, therefore, 17·5 in the red glass, 27·5 in the orange,
45 in the yellow, 42·5 in the green, 47·5 in the blue, 70 in the
indigo, and 15 in the violet. Now, as these absorptions extinguish a
proportional part of each of the rays which constitute the calorific
stream transmitted by common glass, they may be compared, as we said
before, with the absorbent action exercised on light by matters more
or less deeply brown or dark, when they are immersed in water, or some
other colourless liquid which dissolves, but does not affect them
chemically.”--_Annales de Chimie et de Physique_, tom. xl. p. 382.

Guided by these principles, the author selected the glass employed in
glazing the Royal Palm-House, at Kew Botanical Gardens, where it was
desired to obstruct the passage of those rays which have a particular
scorching influence. Of this glass a description was given at the
meeting of the British Association at Oxford, which appears in the
Transactions for that year. The result has been all that could be
desired--not a single instance of scorching having occurred during the
three years which have elapsed.

[45] In the _Philosophical Transactions_, vol. xc., the following
papers, by Sir William Herschel, may be consulted:--

_Investigation of the powers of the prismatic colours to heat
and illuminate objects; with remarks that prove the different
refrangibility of radiant heat. To which is added, an inquiry into the
method of viewing the sun advantageously, with telescopes of large
apertures and high magnifying powers_, p. 255. _Experiments on the
refrangibility of the invisible rays of the sun_, p. 284. _Experiments
on the solar and on the terrestrial rays that occasion heat; with a
comparative view of the laws to which light and heat, or rather the
rays which occasion them, are subject; in order to determine whether
they are the same or different_, pp. 293, 437.

In connection with this inquiry, Sir William Herschel remarks, that
since a _red glass_ stops no less than 692 out of 1,000 such rays as
are of the refrangibility of red light, we have a direct and simple
proof, in the case of the red glass, that the rays of light are
transmitted, while those of heat are stopped, and that thus they have
nothing in common but a certain equal degree of refrangibility, which
by the power of the glass must occasion them to be thrown together into
the place which is pointed out to us by the visibility of the rays of
light.

On the same subject, a Memoir, by Sir Henry Englefield, in the Journal
of the Royal Institution for 1802, p. 202, may be consulted; and
_Researches on Light_, by the Author.

[46] Dr. Draper, _On the production of light by heat_, in the Phil.
Mag. for 1847.

Sir Isaac Newton fixed the temperature at which bodies become
self-luminous at 635°; Sir Humphry Davy at 812°; Mr. Wedgewood at 947°;
and Mr. Daniell at 980°; whilst Dr. Draper from his experiments gives
977°; and Dr. Robinson 865°.

In a review of the above paper by Melloni, entitled _Researches on the
Radiations of Incandescent Bodies, and on the Elementary Colours of the
Solar Spectrum_, translated for Silliman’s Journal for August, 1847, he
remarks:--

“I say that they conduct, as do others heretofore known on light and
radiant heat, to a perfect analogy between the general laws which
govern these two great agents of nature. I will add that I regard
the theory of their identity as the only one admissible by the rules
of philosophy; and that I consider myself obliged to adopt it, until
it shall have been proved to me that there is a necessity of having
recourse to two different principles, for the explanation of a series
of phenomena which at present appear to belong to a solitary agent.”

Reference should also be made to a paper by Dr. Robinson, _On the
effects of Heat in lessening the Affinities of the Elements of Water_,
in the Transactions of the Royal Irish Academy, 1848, where he says
that “when a platinum wire is traversed by a current gradually
increased till it produces ignition, the first gleam that appears is
not red, but of a colour which, when I first saw it, I compared to
the ‘lavender ray’ discovered by Sir John Herschel beyond the violet,
though I was surprised at seeing the tint of that most refrangible ray
preceding the ray which is least so. It is quite conspicuous at about
865°; and as the mode in which it makes its appearance presents nothing
abrupt or discontinuous, it seems likely that it is merely a transition
from invisible rays excited at a lower temperature to ordinary
light.”--p. 310.

[47] In the _Bakerian Lecture_ for 1842, _On the transparency of the
Atmosphere, and the law of extinction of the solar rays in passing
through it_, by James D. Forbes, Esq., F.R.S., &c., will be found a
most complete investigation of this subject.

The experiments were, for the most part, made in Switzerland with Sir
John Herschel’s actinometer, and they prove satisfactorily,--“That
the absorption of the solar rays by the strata of air to which we
have immediate access, is considerable in amount for even moderate
thicknesses.”

[48] After referring to several curious and instructive experiments, in
which peculiar chemical changes are produced under the influence of the
solar rays by their HEAT, Sir John Herschel says:--

“These rays are distinguished from those of Light by being invisible;
they are also distinguished from the pure calorific rays beyond the
spectrum, by their possessing properties (_of a peculiar character,
referred to in former papers_) either exclusively of the calorific
rays, or in a much higher degree. They may perhaps not improperly be
regarded as bearing the same relation to the calorific spectrum which
the photographic rays do to the luminous ones. If the restriction
to these rays of the term _thermic_, as distinct from _calorific_,
be not (as I think, in fact, it is not) a sufficient distinction, I
would propose the term _parathermic rays_ to designate them. These are
the rays which I conceive to be active in producing those singular
molecular affections which determine the precipitation of vapours in
the experiments of Messrs. Draper, Moser, and Hunt, and which will
probably lead to important discoveries as to the intimate nature of
those forces resident on the surfaces of bodies, to which M. Dutrochet
has given the name of epipolic forces.”--_On certain improvements in
Photographic Processes, described in a former communication_ (Phil.
Trans, vol. cxxxiii.); and _On the Parathermic Rays of the Solar
Spectrum_, Phil. Trans, vol. cxxxiv.

The experiments of Mrs. Somerville, _On the Action of the Rays of the
Spectrum on Vegetable Juices_ (Phil. Transactions, vol. cxxxvii.),
appear to connect themselves with this particular class of rays in a
curious manner.

[49] Experiments on the influence of heat on differently-
bodies were first made by Dr. Hooke; and it was not until long after
that Franklin made his ingenious experiments. Davy exposed to sunshine
six equal pieces of copper, painted white, yellow, red, green, blue,
and black, in such a manner that one side only was illuminated. To
the dark side he attached a bit of cerate, ascertained by experiment
to melt at 700. The cerate attached to the black became fluid first,
the blue next, then the green and red, and lastly the yellow and
white.--Beddoes’s _Contributions to Physical Knowledge_, and collected
works of Sir Humphry Davy, vol. ii. p. 27.

[50] By reference to the Treatise on Heat, in the _Encyclopædia
Metropolitana_, numerous suggestive experiments will be found, all
bearing on this subject. Peschel’s _Elements of Physics_ may also be
consulted with advantage. The fact is, however, simply proved, as
stated in the text, by placing the bulbs of delicate thermometers,
so as to be completely involved in the petals of flowers exposed to
sunshine, shading the upper portion of the stem of the instrument.

[51] Moser, _On Vision, and on the Action of Light on Bodies_: and also
_On Latent Light_: Scientific Memoirs, vol. iii. Draper, _On certain
Spectral Appearances, and on the Discovery of Latent Light_: Phil.
Mag., Nov. 1842.

[52] A particular examination of this curious question will be found in
the Author’s report _On the Influence of the Solar Rays on the Growth
of Plants_: Reports of the British Association for 1847.

[53] Ammianus Marcellinus ascribes the longevity and robust health of
mountaineers to their exposure to the dews of night. Dew was employed
by the alchemists in their experiments on the solution of gold. The
ladies of old collected the “celestial wash,” which they imagined had
the virtue of preserving their fine forms, by exposing heaps of wool
to the influences of night radiation. It was supposed that the lean
features of the grasshopper arose from that insect feeding entirely on
dew: “Dumque thymo pascentur apes, dum rore cicadæ,” Virgil, Eclog.

See some curious remarks by Boyle, _On the Power of Dew in Working on
Solid Bodies_: Works of the Honourable R. Boyle, vol. v. p. 121. 1744.

[54] See the _Researches on Heat_, by Professor James Forbes, in the
Transactions of the Royal Society of Edinburgh; also Melloni’s papers
on the same subject in the _Annales de Chimie_, several of which have
been translated into the _Scientific Memoirs_, edited by Mr. Richard
Taylor.

[55] The phenomena of dew have constantly engaged the attention of
man. Aristotle, in his book _De Mundo_, puts forth some just notions
on its nature. An opinion has almost always prevailed that dew falls.
Gersten appears to have been the first who opposed this motion. He was
followed by Musschenbroek, and then by Du Fay. The researches of Leslie
were of a far more exact character. Dr. Wilson, in the Transactions of
the Royal Society of Edinburgh, 1st vol., published a _Memoir on Hoar
Frost_ of much interest; but the questions involved remained unsettled
until the researches of Dr. Wells, which were published in his _Essay
on Dew_.

[56] By far the most complete set of experiments on the radiation
of heat from the surface at night, which have been published since
Dr. Wells’s memoir _On Dew_, are those of Mr. Glaisher, of the Royal
Observatory at Greenwich. Instruments of the most perfect kind were
employed, and the observations made with sedulous care. The results
will be found in a memoir _On the Amount of the Radiation of Heat, at
night, from the Earth, and from various bodies placed on or near the
Surface of the Earth_, by James Glaisher, Esq., Philosophical Trans.
for 1847, part 2.

[57] Dr. Wells noticed the practical fact that very light shades
protected delicate plants from frost, by preventing radiation. Mr.
Goldsworthy Gurney has made a series of interesting experiments, and
he imagines that by shading grasslands with boughs of trees, or any
light litter, a more abundant crop is produced. The subject has been
discussed in the journals of the Royal Agricultural Society. May not
the apparent increase be due entirely to the succulent condition in
which a plant always grows in the shade?

[58] This paper of Melloni’s will be found in the _Bibliothèque
Universelle de Genève_, for 1843. The conclusions are highly ingenious,
but they rest entirely on the analogy supposed to be discovered
between the relations of heat, like light, to the  rays of the
spectrum. This, it must be remembered, is not the case, since even Sir
William Herschel showed that red light might exist with only a minimum
of calorific power, notwithstanding the fact, that the maximum heat-ray
of the spectrum coincides with the red rays.

[59] Dr. Robinson, of Armagh, in his Memoir _On the Effects of Heat in
lessening the Affinities of the Elements of Water_.--Transactions of
the Royal Irish Academy, vol. xxi. part 2.

[60] On this subject consult Robert Were Fox, _On the Temperature of
the Mines of Cornwall_.--Cornwall Geological Transactions, vol. ii.; W.
J. Henwood, on the same subject, _Ib._ vol. v.; Reports of the British
Association, 1840, p. 315; Edinburgh New Philosophical Journal, vol.
xxiv. p. 140.

[61] _On the causes of the temperature of Hot and Thermal Springs;
and on the bearings of this subject as connected with the general
question regarding the internal temperature of the Earth_: by Professor
Gustav Bischoff, of Bonn.--Edinburgh New Philosophical Journal, vol.
xx. p. 376; vol. xxiii. p. 330. Some interesting information on
the temperature of the ground will be found in Erman’s _Travels in
Siberia_, translated by W. D. Cooley, vol. i. p. 339; vol. ii. p.
366. _Sur la Profondeur à laquelle se trouve la couche de Température
invariable entre les Tropiques_, by Boussingault: Annales de Chimie et
de Physique, 1833, p. 225. Reference may also be made to Humboldt’s
_Cosmos_, Otto’s translation; and to the excellent article on
_Meteorology_, by George Harvey, in the Encyclopædia Metropolitana.
These chthonisothermal lines, as they are called, have been traced by
Humboldt and others over extensive districts.

[62] These results are obtained from the valuable observations
of Robert Were Fox, Esq., made with great care by that gentleman
in several of the Cornish mines: _Report on some observations on
Subterranean Temperature_.--British Association Reports, vol. ix. p.
309; Philosophical Magazine, 1837, vol. ii. p. 520.

[63] From his experiments, the following conclusions were arrived at by
M. Delaroche:--

1. Invisible radiant heat may, in some circumstances, pass directly
through glass.

2. The quantity of radiant heat which passes directly through glass
is so much greater, relative to the whole heat emitted in the same
direction, as the temperature of the source of heat is more elevated.

3. The calorific rays which have already passed through a screen of
glass, experience, in passing through a second glass screen of a
similar nature, a much smaller diminution of their intensity than they
did in passing through the first screen.

4. The rays emitted by a hot body differ from each other in their
faculty to pass through glass.

5. A thick glass, though as much or more permeable to light than a thin
glass of worse quality, allows a much smaller quantity of radiant heat
to pass. The difference is so much the less as the temperature of the
radiating source is more elevated.

6. The quantity of heat which a hot body yields in a given time, by
radiation to a cold body situate at a distance, increases, _cæteris
paribus_, in a greater ratio than the excess of temperature of the
first body above the second.--Journal de Physique, vol. lxxv.

[64] Sir David Brewster differs from the conclusions arrived at by
Delaroche. He thus explains his views:--“The inability of radiant
heat to pass through glass, may be considered as a consequence of its
refusing to yield to the refractive force; for we can scarcely conceive
a particle of radiant matter freely permeating a solid body, without
suffering some change in its velocity and direction. The ingenious
experiments of M. Prévost, of Geneva, and the more recent ones of
M. Delaroche, have been considered as establishing the permeability
of glass to radiant heat. M. Prévost employed moveable screens of
glass, and renewed them continually, in order that the result which
he obtained might not be ascribed to the heating of the screen; but
such is the rapidity with which heat is propagated through a thin
plate of glass, that it is extremely difficult, if not impossible, to
observe the state of the thermometer before it has been affected by
the secondary radiation from the screen. The method employed by M.
Delaroche, of observing the difference of effect, when a blackened
glass screen and a transparent one were made successively to intercept
the radiant heat, is liable to an obvious error. The radiant heat would
find a quicker passage through the transparent screen; and, therefore,
the difference of effect was not due to the transmitted heat, but to
the heat radiated from the anterior surface. The truth contained in M.
Delaroche’s fifth proposition is almost a demonstration of the fallacy
of all those that precede it. He found that ‘a thick plate of glass,
though as much or more permeable to light than a thin glass of worse
quality, allowed a much smaller quantity of radiant heat to pass.’ If
he had employed very thick plates of the purest flint glass, or thick
masses of fluid that have the power of transmitting light copiously,
he would have found that not a single particle of heat was capable of
passing directly through transparent media.”--Sir D. Brewster, _On new
properties of heat as exhibited in its propagation along plates of
glass_. Philosophical Transactions, vol. cvi. p. 107.

[65] _Proposal of a New Nomenclature for the Science of Calorific
Radiations_, by M. Melloni. Bibliothèque Universelle de Genève, No.
70. Scientific Memoirs, vol. iii. part 12. Many of the terms, as
_Diathermasy_, or transparency for heat; _Adiathermasy_, opacity for
heat; _Thermochroic_,  for heat, and others, are valuable
suggestions of forms of expression which are required in dealing with
these physical phenomena.

[66] For a careful examination of the several theories of heat consult
Dr. Young’s Course of Lectures on Natural Philosophy, &c., Lecture 52,
_On the Measures and the Nature of Heat_; also Powell’s very excellent
_Reports on Radiant Heat_--Reports of the British Association, 1832,
1840. The transcendental view which the immaterial theory leads to,
cannot be better exemplified than by the following quotation from that
inexplicable dream of a talented man, _Elements of Physiophilosophy_,
by Lorenz Oken, M.D. (translated for the Ray Society, by Alfred Tulk):--

“Heat is not matter itself any more than light is; but it is only the
act of motion in the primary matter. In heat, as well as in light,
there certainly resides a material substratum; yet, this substratum
does not give out heat and light; but the _motion_ only of the
substratum gives out heat, and the _tension_ only of the substratum
light. There is no body of heat; nitrogen is the body of heat, just
as oxygen may be called the body of fire. Heat is real space; into it
all forms have been resolved, as all materiality has been resolved
into gravity, and all activity, all polarity, into light. Heat is the
universal form, consequently the want of form.”

[67] Mémoires de la Société Physique, &c., de Genève, tom. ii. art. 2.

[68] This curious phenomenon was first observed by Mr. Trevelyan, whose
_Notice regarding some Experiments on the Vibration of Heated Metals_
will be found in the Transactions of the Royal Society of Edinburgh,
vol. xii., 1837. In a Memoir in the same volume, entitled _Experimental
Researches regarding certain vibrations which take place between
metallic masses having different temperatures_, Professor Forbes draws
the following conclusions:--

1. “The vibrations never take place between substances of the same
nature.

2. “Both substances must be metallic. (This is now proved not to be
necessary.)

3. “The vibrations take place with an intensity proportional (within
certain limits) to the difference of the conducting powers of the
metals for heat or electricity; the metal having the least conducting
power being necessarily the coldest.

4. “The time of contact of two points of the metals must be longer than
that of the intermediate portions.

5. “The impulse is received by a distinct and separate process at each
contact of the bar and block, and in no case is the metallic connection
of the bearing points in the bar, or those of the block, in any way
essential.

6. “The intensity of the vibration is (under certain exceptions)
proportional to the difference of temperature of the
metals.”--Transactions of the Royal Society of Edinburgh, vol. xii.

[69] The Bakerian Lecture. _On certain Phenomena of Voltaic Ignition,
and the Decomposition of Water into its Constituent Gases by Heat_: by
W. R. Grove, Esq.--Philosophical Transactions, 1847. Part 1.

[70] Davy’s _Researches on Flame_. Works, vol. vi.--Philosophical
Transactions for 1817.

[71] _On the Effect of Heat in lessening the affinities of the Elements
of Water_: by the Rev. Thomas Romney Robinson, D.D.--Transactions of
the Royal Irish Academy, vol. xxi. part 2.

[72] _An Inquiry concerning the Chemical Properties that have been
attributed to Light_: by Benjamin, Count of Rumford.--Philosophical
Transactions, vol. lxxxviii. p. 449.--The results obtained by Count
Rumford were probably due to the non-luminous heat-rays--parathermic
rays--which are known to be given off by boiling water.

[73] For Dr. Drapers paper, see Philosophical Magazine for May, 1847,
vol. xxx. 3rd series.

[74] _On the Action of the Rays of the Solar Spectrum on Vegetable
Colours_: by Sir J. F. W. Herschel, Bart.

The proof of the continuation of the visible prismatic spectrum beyond
the extreme violet may be witnessed in the following manner:--“Paper
stained with tincture of turmeric is of a yellow colour; and, in
consequence, the spectrum thrown in it, if exposed in open daylight,
is considerably affected in its apparent colours, the blue portion
appearing violet, and the violet very pale and faint; but beyond the
region occupied by the violet rays, is distinctly to be seen a faint
prolongation of the spectrum, terminated laterally, like the rest of
it, by straight and sharp outlines, and which, in this case, affects
the eye with the sensation of a pale yellow colour.”--Philosophical
Transactions, p. 133.

[75] The most complete exposition of the theory that animal heat is
derived from chemical action only, will be found in _Animal Chemistry,
or Chemistry in its applications to Physiology and Pathology_, by
Justus Liebig: translated by Dr. Gregory. The conclusions arrived at
by the author, notwithstanding his high--and deservedly high--position
in chemical science, must, however, be received with great caution,
many of them being founded on most incorrect premises, and his
generalizations being of the most hasty and imperfect character. At
page 22 the following passage occurs:--“If we were to go naked, like
certain savage tribes, or if in hunting or fishing we were exposed
to the same degree of cold as the Samoiedes, we should be able, with
ease, to consume ten pounds of flesh, and, perhaps, a dozen of tallow
candles into the bargain, daily, as warmly clad travellers have related
with astonishment of these people. We should then also be able to take
the same quantity of brandy or train-oil without bad effects, because
the carbon and hydrogen of these substances would only suffice to keep
up the equilibrium between the external temperature and that of our
bodies.”

A brief examination will exhibit the error of this. The analysis of
Beef, by D. Lyon Playfair, is as follows:--

    Carbon      51·83
    Hydrogen     7·57
    Nitrogen    15·01
    Oxygen      21·37
    Ashes        4·23

And the following has been given by Chevreul as the composition of
mutton tallow:--

    Carbon   96
    Hydrogen 16
    Nitrogen 16
    Oxygen   48

About three times the quantity of oxygen to the carbon eaten, is
required to convert it into carbonic acid; hence, the Samoiede, eating
more highly carbonized matter, must inspire 288 oz. of oxygen daily,
or nearly eight times as much as the “ordinary adult.” By the lungs
he must take into the body 2,304 cubic feet of air besides what will
be absorbed by the skin. His respirations must be so much quickened,
that at the lowest possible calculation he must have 500 pulsations a
minute. Under such conditions it is quite clear man could not exist.
There is no disputing the fact of the enormous appetites of these
people; but all the food is not removed from the system as carbonic
acid gas.

[76] An interesting paper by Dr. Davy, _On the Temperature of Man_,
will be found in the Philosophical Transactions, vol. cxxxvi. p.
319.--Sir Humphry Davy, in his _Consolations in Travel, or the Last
Days of a Philosopher_, in his fourth dialogue, _The Proteus_, has
several ingenious speculations on this subject.

[77] _Exposé de quelques résultats obtenus par l’action combinée de la
chaleur et de la compression sur certains liquides, tels que l’eau,
l’alcool, l’éther sulfurique, et l’essence de pétrole rectifiée_: par
M. le Baron Cagniard de la Tour.

The three following conclusions are arrived at:--

1. Que l’alcool à 36 degrés, l’essence de pétrole rectifiée à 42
degrés, et l’éther sulfurique soumis à l’action de la chaleur et de la
compression, sont susceptibles de se réduire complètement en vapeur
sous un volume un peu plus que double de celui de chaque liquide.

2. Qu’une augmentation de pression, occasionnée par la présence de
l’air dans plusieurs des experiences qui viennent d’être citées, n’a
point apporté d’obstacle à l’évaporation du liquide dans le même
espace; qu’elle a seulement rendu sa dilatation plus calme et plus
facile à suivre jusqu’au moment où le liquide semble s’évanouir
tout-à-coup.

3. Que l’eau, quoique susceptible sans doute d’être réduite en vapeur
très-comprimée, n’a pu être soumise à des experiences complètes,
faute de moyens suffisans pour assurer l’exacte fermeture de la
marmite de compression, non plus que dans les tubes de verre dont elle
altère la transparence en s’emparant de l’alcali qui entre dans leur
composition.--Annales de Chimie, vol. xxi.

[78] _Sur les phénomènes qui présentent les corps projetés sur des
surfaces chaudes_: par M. Boutigny (d’Evreux).--Annales de Chimie et de
Physique, vol. xi. p. 16. _Congélation du mercure en trois secondes,
en vertu de l’état sphéroïdal dans un creuset incandescent_: by M.
Faraday.--Ibid., vol. xix. p. 383.

_Spheroidal Condition of Bodies_ (Extrait d’une Note de M. Boutigny
d’Evreux).

“Au nombre des propriétés des corps à l’état sphéroïdal, il en est cinq
qui me paraissent caractéristiques et fondamentales, et c’est sur ces
cinq propriétés que je base la définition que je soumets aujourd’hui au
jugement de l’Académie. Ces cinq propriétés sont:--

“1. La forme arrondie que prend la matière sur une surface chauffée à
une certaine température.

“2. Le fait de la distance permanente qui existe entre le corps à
l’état sphéroïdal et le corps sphéroïdalisant.

“3. La propriété de réfléchir le calorique rayonnant.

“4. La suspension de l’action chimique.

“5. La fixité de la température des corps à l’état sphéroïdal.

“Cela posé, voici la définition que je propose: un corps projeté sur
une surface chaude est à l’état sphéroïdal quand il revêt la forme
arrondie et qu’il se maintient sur cette surface au delà du rayon de sa
sphère d’activité physique et chimique; alors il réfléchit le calorique
rayonnant, et ses molécules sont, quant à la chaleur, dans un état
d’équilibre stable; c’est-à-dire, à une température invariable, ou qui
ne varie que dans des limites étroites.”--Comptes Rendus, 6 Mars, 1848.

[79] _Some Facts relative to the Spheroidal State of Bodies, Fire
Ordeal, Incombustible Man, &c._: by P. H. Boutigny (d’Evreux),
Philosophical Magazine, No. 233 (third, series), p. 80; Comptes Rendus,
May 14, 1849.

[80] The theory of freezing mixtures is deduced from the doctrine of
latent caloric. These are mixtures of saline substances which, at the
common temperature, by their mutual chemical action, pass rapidly into
the fluid form, or are capable of being rapidly dissolved in water,
and, by this quick transition to fluidity, absorb caloric, and produce
degrees of cold more or less intense.--Rev. Francis Lunn, _On Heat_:
Encyclopædia Metropolitana.

[81] _Propriétés de l’Acide Carbonique liquide_, par M. Thilorier,
Annales de Chimie, vol. lx. p. 427. _Solidification de l’Acide
Carbonique_: Ibid. p. 432.

[82] _On the Liquefaction and Solidification of Bodies generally
existing as Gases_, by Michael Faraday, D.C.L., F.R.S., &c.;
Philosophical Transactions, vol. cxxxvi, p. 155.

[83] Burns, in one of his most natural and pathetic letters.




CHAPTER VII.

LIGHT.

  Theories of the Nature of Light--Hypotheses of Newton
    and Huygens--Sources of Light--The Sun--Velocity of
    Light--Transparency--Dark Lines of the Spectrum--Absorption
    of Light--Colour--Prismatic Analysis--Rays of the
    Spectrum--Rainbow--Diffraction--Interference--Goethe’s
    Theory--Polarisation--Magnetisation of Light--Vision--The
    Eye--Analogy--Sound and Light--Influence of Light on Animals and
    Vegetables--Phosphorescence arising from several Causes--Artificial
    Light--Its Colour dependent on Matter.


Light, the first creation, presents to the enquiring mind a series
of phenomena of the most exalted character. The glowing sunshine,
painting the earth with all the brilliancy of colour, and giving to the
landscape the inimitable charm of every degree of illumination, from
the grey shadow to the golden glow;--the calm of evening, when, weary
of the “excess of splendour,” the eye can repose in tranquillity upon
the “cloud-land” of the west, and watch the golden and the ruddy hues
fade slowly into the blue tincture of night;--and the pale refulgence
of the moon, with the quiet sparkle of the sun-lit stars,--all tend
to impress upon the soul, the great truth that, where there is light,
organisation and life are found, and beyond its influence death and
silence hold supreme dominion.[84] Through all time we have evidences
that this has been the prevailing feeling of the human race, derived,
of course, from their observation of the natural phenomena dependent
upon luminous agency. In the myths of every country, impersonations of
light prevail, and to these are referred the mysteries of the perpetual
renewal of life on the surface of the earth.

This presentiment of a philosophic truth, in the instance of the poet
sages of intellectual Greece, was advanced to the highest degree of
refinement; and the sublime exclamation of Plato: “Light is truth, and
God is light,” approaches nearly to a divine revelation.

As the medium of vision--as the cause of colour--as a power influencing
in a most striking manner all the forms of organisation around us,
light presented to the inquiring minds of all ages a subject of the
highest interest.

The ancient philosophers, although they lost themselves in the
metaphysical subtleties of their schools, could not but discover in
light an element of the utmost importance in natural operations. The
alchemists regarded the luminous principle as a most subtile fluid,
capable of interpenetrating and mingling with gross matter: gold
being supposed to differ from the baser metals only in containing a
larger quantity of this ethereal essence.[85] Modern science, after
investigating most attentively a greater number of the phenomena of
light, has endeavoured to assist the inquiry by the aid of hypotheses.
Newton, in a theory, which exhibits the refined character of that
great philosopher’s mind, supposes luminous particles to dart from the
surfaces of bodies in all directions--that these infinitely minute
particles are influenced by the attracting and repelling forces of
matter, and thus turned back, or reflected, from their superficies in
some cases, and absorbed into their interstitial spaces in others.

Huyghens, on the contrary, supposes light to be caused by the waves or
vibrations of an infinitely elastic medium--ETHER--diffused through all
space, which waves are propagated in every direction from the luminous
body. In the first theory, a luminous particle is supposed actually to
come from the sun to the earth; in the other, the sun only occasions a
disturbance of the _ether_, which extends with great rapidity, in the
same manner as a wave spreads itself over the surface of a lake.

Nearly all the facts known in the time of Newton, and those discovered
by him, were explained most satisfactorily by his hypothesis; but
it was found they could be interpreted equally as the effects of
undulation, with the exception of the production of colour by prismatic
refraction. Although the labours of many gifted minds have been given,
with the utmost devotion, to the support of the vibratory theory,
this simple fact has never yet received any satisfactory explanation;
and there are numerous discoveries connected with the molecular and
chemical disturbances produced by the sun’s rays, which do not appear
to be explained by the hypothesis of emission or of undulation.

In both theories a wave motion is admitted, and every fact renders
it probable that this mode of progression applies not only to light,
but to the so-called _imponderable forces_ in general. Admitting,
therefore, the undulatory movement of luminous rays, we shall not stop
to consider those points of the discussion which have been so ably
dealt with by Young, Laplace, Fresnel, Biot, Fraunhofer, Herschel,
Brewster, and others, but proceed at once to consider the sources of
light, and its more remarkable phenomena.[86]

The sun is the greatest permanently luminous body we are acquainted
with, and that orb is continually pouring off light from its surface
in all directions at the rate, through the resisting medium of space
and of our own atmosphere, of 192,000 miles in a second of time. It has
been calculated, however, that light would move through a vacuum with
the speed of 192,500 miles in the same period. We, therefore, learn
that a ray of light requires eight minutes and thirteen seconds to
come from the sun to us. In travelling from the distant planet Uranus,
nearly three hours are exhausted; and from the nearest of the fixed
stars each ray of light requires more than six years to traverse the
intervening space between it and the earth. Allow the mind to advance
to the regions of nebulæ, and it will be found that hundreds of years
must glide away during the passage of their radiations. Consequently,
if one of those masses of matter, or even one of the remote fixed
stars, was “blotted out of heaven” to-day, several generations of
the finite inhabitants of this world would fade out of time before
the obliteration could be known to man. Here the immensity of space
assists us in our conception, limited though it be, of the for-ever of
eternity.[87]

All the planets of our system shine with reflected light, and the
moon, our satellite, also owes her silvery lustre to the sun’s
radiations. The fixed stars are, in all probability, suns shining from
the far distance of space, with their own self-emitted lights. By the
photometric researches of Dr. Wollaston, we learn, however, that it
would take 20,000 millions of such orbs as Sirius, the brightest of the
fixed stars, to afford as much light as we derive from the sun. The
same observer has proved that the brightest effulgence of the full moon
is yet 801,072 times less than the luminous power of our solar centre.

The cultivators of modern science are a bold race; not contented with
endeavouring to understand the physical earth, they are endeavouring
to comprehend the condition of the solar surface. The mind of man can
penetrate far into nature, and, as it were, feel out the mysteries of
untraversed space. The astronomer learns of a peculiar condition of
light, which is termed polarisation, and he learns by this, too, that
he can determine if from a bright luminous disc the light is derived
from a solid mass in a state of intense ignition, or from vapour in
an incandescent condition. He adds a polarising apparatus to his
telescopes, and he determines that the light we derive from the sun
is due to an envelope of vapour--burning, in all probability--only
with greater intensity, as the gas which we now employ. This
_Photosphere_--as it has been called by the late French philosopher
Arago, is found to be subjected to violent disturbances, and the dark
spots seen on the sun’s disc are now known to be openings through this
mysterious envelope of light, which enable us to look in upon the dark
body of the sun itself.

Luminous phenomena may be produced by various means--chemical action
is a source of light; and, under several circumstances in which the
laws of affinity are strongly exerted, a very intense luminous effect
is produced. Under this head all the phenomena of combustion are
included. In the electric spark we have the development of light;
and the arc which is formed between charcoal points at the poles of
a powerful voltaic battery affords us the most intense artificial
illumination with which we are acquainted. In addition to these, we
have the peculiar phenomena of phosphorescence arising from chemical,
calorific, electrical, actinic, and vital excitation, all of which must
be particularly examined.

From whatever source we procure light, it is the same in character,
differing only in intensity. In its action upon matter, we have the
phenomena of transmission, of reflection, of refraction, of colour, of
polarisation, and of vision, to engage our attention.

A beam of white light falls upon a plate of colourless glass, and it
passes freely through it, losing but little of its intensity; the
largest portion being lost by reflection from the first surface upon
which the light impinges. If the glass is roughened by grinding, we
lose more light by absorption and by reflection from the asperities of
the roughened surface; but if we cover that face with any oleaginous
fluid, as, for instance, turpentine, its transparency is restored. We
have thus direct proof that transparency to light is due to molecular
condition. This may be most strikingly shown by an interesting
experiment of Sir David Brewster’s:--

If a glass tube is filled with nitrous acid vapour, which is of a dull
red colour, it admits freely the passage of the red and orange rays
with some of the others, and, if held upright in the sunshine, casts
a red shadow on the ground; by gently warming it with a spirit-lamp,
whilst in this position, it acquires a much deeper and blacker colour,
and becomes almost impervious to any of the rays of light; but upon
cooling it again recovers its transparency.

It has also been stated by the same exact experimentalist, that having
brought a purple glass to a red heat, its transparency was improved, so
that it transmitted green, yellow, and red rays, which it previously
absorbed; but the glass recovered its absorptive powers as it cooled.
A piece of yellowish-green glass lost its transparency almost entirely
by being heated. Native yellow orpiment becomes blood-red upon being
warmed, when nearly all but the red rays are absorbed; and pure
phosphorus, which is of a pale yellow colour, and transmits freely all
the  rays upon being melted, becomes very dark, and transmits
no light.

Chemistry affords numerous examples of a very slight change of
condition, producing absolute opacity in fluids which were previously
diaphanous.[88]

Charcoal absorbs all the light which falls upon it, but in some
of its states of combination, and in the diamond, which is pure
carbon, it is highly transparent. Gold and silver beaten into thin
leaves are permeated by the green and blue rays, and the metals in
combination with acids are all of them more or less transparent. What
becomes of the light which falls upon and is absorbed by bodies,
is a question which we cannot yet, notwithstanding the extensive
observations that have been made by some of the most gifted of men,
answer satisfactorily. In all probability, as already stated, it
is permanently retained within their substances; and many of the
experiments of exciting light in bodies when in perfect darkness, by
the electric spark and other means, appear to support the idea of light
becoming latent or hidden.

No body is absolutely transparent; some light is lost in passing even
through ethereal space, and still more in traversing our atmosphere.

Amongst the most curious instances of absorption is that which is
uniformly discovered in the solar spectrum, particularly when we
examine it with a telescope. We then find that the  rays are
crossed by a great number of dark bands or lines, giving no light;
these are generally called Fraunhofer’s dark lines, as it was to the
indefatigable exertions of that experimentalist, and by the aid of his
beautiful instruments, that most of them were discovered and measured,
and enumerated, although they were previously noticed by Dr. Wollaston.
It is quite clear that those lines represent rays which have been
absorbed in their passage from the sun to the earth: although some
of them have no doubt undergone absorption within the limits of the
earth’s atmosphere, we have every reason to believe, with Sir John
Herschel, that the principal absorption takes place in the atmosphere
of the sun.[89]

It has been proved by Dr. Miller, that the number of those dark
lines is continually varying with the alteration of atmospheric
conditions;[90] and the evidences which have been afforded, of peculiar
states of absorption by the gaseous envelope of the earth,--during the
prosecution of investigations on the chemical agencies of the sun’s
rays,--are of a sufficiently convincing character.

It has been calculated by Bouguer, that if our atmosphere, in its
purest state, could be extended rather more than 700 miles from the
earth’s surface instead of nearly 40, as it is at present, the sun’s
rays could not penetrate it, and this globe would roll on in darkness
and silence, without a vestige of vegetable form or of animal life. In
the Hebrew version of the Mosaic History, the reading is, “Let light
appear:” may not this really mean that the earth’s atmosphere was so
cleared of obstructing vapours, that the solar rays were enabled to
reach the earth? The same calculation supposes that sea-water loses
all its transparency at the depth of 730 feet; but a dim twilight must
prevail much deeper in the ocean.

The researches of Professor Edward Forbes have proved, that at the
depth of 230 fathoms in the Ægean sea, the few shelled animals that
exist are colourless: no plants are found within that zone; and that
industrious naturalist fixes the zero of animal life of those waters at
about 300 fathoms.[91] Since these zones mark the rapidly diminishing
light, it is evident that where life ceases to be must be beyond the
limits to which life can penetrate.

Our atmosphere, charged with aqueous vapour, serves to shield us from
the intense action of the solar powers. By it we are protected from
the destructive influences of the sun’s light and heat; enjoy those
modified conditions which are most conducive to the healthful being of
organic forms; to it we owe “the blue sky bending over all,” and those
beauties of morning and evening twilight of which

    ---- Sound and motion own the potent sway.
    Responding to the charm with its own mystery.

To defective transparency, or rather to the different degrees of it, we
must attribute, in part, the colours of permeable media. Thus, a glass
or fluid appears yellow to the eye, because it has the property of
admitting the permeation of a larger quantity of the yellow rays than
of any others;--red, because the red rays pass it with the greatest
freedom; and so on for every other colour. In most cases the powers of
transmission and of reflection are similar; but it is not so in all; a
variety of fluor spar, which, while it transmits green light, reflects
blue, and the precious opal, are striking instances to the contrary.
Some glasses, which transmit yellow light have the singular power of
dispersing blue rays from one surface; and a solution of quinine in
water acidulated with sulphuric acid, although perfectly transparent
and colourless when held between the eye and the light, exhibits, if
viewed in a particular direction, a lively cerulean tint. These effects
being supposed to be due to the conditions of the surface, have been
called _epipolic_ phenomena.[92]

The careful investigation of these phenomena has made us acquainted
with some very interesting facts, and indeed discovered to us a set
of luminous rays which were previously unknown. The dispersion of
blue light from the surface of some yellow glasses--such as have been
 by the oxide of silver--is of a different order from that
which takes place with the solution of sulphate of quinine, or with
the fluor spar. The first depends upon a peculiar condition of the
surface, while the latter phenomena are due to a dispersion which
takes place _within_ the solid or fluid. In addition to the sulphate
of quinine, and the fluor spar, we obtain the same results in a very
marked manner by a canary yellow glass,  with the oxide of
uranium, and by a decoction of the inner bark of the horse-chesnut
tree. Mr. Stokes, who has investigated this class of phenomena, and
proposes to call it _Fluorescence_, from its being naturally seen in
fluor-spar, has shown that the peculiar internal dispersion, and the
consequent alteration of the colour of the ray, is due to an alteration
in its refrangibility. Whether this hypothesis prove to be the correct
one or not, it is certain that there exists a set of rays of far higher
refrangibility than those seen in the ordinary Newtonian spectrum. This
may be shown in the following manner: taking either of the solutions
named, or a block of uranium glass, throw upon one face, by means of
a prism, a very pure spectrum. On looking _into_ the glass or fluid
there will be seen, commencing amidst the most refrangible rays, a
new set of spectral rays, struggling to make their way through the
absorbent medium. These are of a blue colour in the quinine or chesnut
solution, and green in the uranium glass, and are seen extending
themselves far beyond the most refrangible rays of the ordinary
Newtonian spectrum. This is the space over which those rays which
have the power of producing chemical changes, such as are rendered
familiar by the practice of Photography, are detected in their greatest
activity. It has, therefore, been supposed that these fluorescent rays
are the chemical rays rendered luminous by the alteration of their
refrangibility. This view has received much support from the fact that
the extra spectral rays are crossed with numerous dark lines, and that
in the chemical impressions these lines are marked by unchanged spaces
which exactly coincide with them. There is, however, much doubt of the
correctness of this, since, in the uranium glass of such a thickness
that these visible rays are quite absorbed, the chemical rays still
pass.

However, the whole question requires, and is receiving, the most
searching investigation. The discovery of these phenomena, which are
included under the term of Fluorescence, is of that interesting and
important character, that it must be ranked as the most decided advance
which has been made in physical optics since the days of Newton.

It is not improbable that those rays of such high refrangibility may,
although they are under ordinary circumstances invisible to the human
eye, be adapted to produce the necessary degree of excitement upon
which vision depends in the optic nerves of the night-roaming animals.
The bat, the owl, and the cat, may see in the gloom of night by the aid
of rays which are invisible to, or inactive on the eyes of man, or of
those animals which require the light of day for perfect vision.

It is a general law of the radiant forces, that whenever they fall upon
any surface, a portion is thrown back or reflected at the same time
as other portions are absorbed or transmitted. Upon this peculiarity
appear to depend the phenomena of natural colour in bodies.

The white light of the sun is well known to be composed of several
 rays. Or rather, according to the theory of undulations, when
the rate at which a ray vibrates is altered, a different sensation
is produced upon the optic nerve. The analytical examination of
this question shows, that to produce a red colour the ray of light
must give 37,640 undulations in an inch, and 458,000000,000000 in
a second. Yellow light requires 44,000 undulations in an inch, and
535,000000,000000 in a second; whilst the effect of blue results from
51,110 undulations within an inch, and 622,000000,000000 of waves in
a second of time.[93] The determination of such points as these is
among the highest refinements of science, and, when contrasted with the
most sublime efforts of the imagination, they must appear immeasurably
superior.

If a body sends back white light unchanged, it appears white; if the
surface has the property of altering the vibration to that degree which
is calculated to produce redness, the result is a red colour: the
annihilation of the undulations produces blackness. By the other view,
or the corpuscular hypothesis, the beam of white light is supposed to
consist of certain  rays, each of which has physical properties
peculiar to itself, and thus is capable of producing different
physiological effects. These rays falling upon a transparent or an
opaque body suffer more or less absorption, and being thus dissevered,
we have the effect of colour. A red body absorbs all the rays but the
red; a blue surface, all but the blue; a yellow, all but the yellow;
and a black surface absorbs the whole of the light which falls upon it.

That natural colours are the result of white light, and not innate
properties of the bodies themselves, is most conclusively shown by
placing  bodies in monochromatic light of another kind, when
they will appear either of the colour of that light, or, by absorbing
it, become black; whereas, when placed in light of their own character,
the intensity of colour is greatly increasing.

Every surface has, therefore, a peculiar constitution, by which it
gives rise to the diversified hues of nature. The rich and lively
green, which so abundantly overspreads the surface of the earth, the
varied colours of the flowers, and the numberless tints of animals,
together with all those of the productions of the mineral kingdom,
and of the artificial combinations of chemical manufacture, result
from powers by which the relations of matter to light are rendered
permanent, until its physical conditions undergo some change.

There is a remarkable correspondence between the geographical position
of a region and the colours of its plants and animals. Within the
tropics, where

    “The sun shines for ever unchangeably bright,”

the darkest green prevails over the leaves of plants; the flowers
and fruits are tinctured with colours of the deepest dye, whilst the
plumage of the birds is of the most variegated description and of the
richest hues. In the people also of these climes there is manifested
a desire for the most striking colours, and their dresses have all
a distinguishing character, not of shape merely, but of chromatic
arrangement. In the temperate climates everything is of a more subdued
variety: the flowers are less bright of hue; the prevailing tint of the
winged tribes is a russet brown; and the dresses of the inhabitants of
these regions are of a sombre character. In the colder portions of the
earth there is but little colour; the flowers are generally white or
yellow, and the animals exhibit no other contrast than that which white
and black afford. A chromatic scale might be formed, its maximum point
being at the equator, and its minimum at the poles.[94]

The influence of light on the colours of organized creation is well
shown in the sea. Near the shores we find sea-weeds of the most
beautiful hues, particularly on the rocks which are left dry by the
tides; and the rich tints of the actiniæ, which inhabit shallow water,
must have been often observed. The fishes which swim near the surface
are also distinguished by the variety of their colours, whereas those
which live at greater depths are grey, brown, or black. It has been
found that after a certain depth, where the quantity of light is so
reduced that a mere twilight prevails, the inhabitants of the ocean
become nearly colourless. That the sun’s ray alone gives to plants the
property of reflecting colour is proved by the process of blanching, or
_etiolation_, produced by artificially excluding the light.

By a triangular piece of glass--a prism,--we are enabled to resolve
light into its ultimate rays. The white pencil of light which falls
on the first surface of the prism is bent from its path, and 
bands of different colours are obtained. These bands or rays observe a
curious constancy in their positions: the red ray is always the least
bent out of the straight path: the yellow class comes next in the
order of refrangibility; and the blue are the most diverted from the
vertex of the prism. The largest amount of illuminating power exists
in the yellow ray, and it diminishes towards either end.[95] It is not
uninteresting to observe something like the same variety of colour
occurring at each end of the prismatic spectrum. The strict order
in which the pure and mixed  rays present themselves is as
follows:--

1. The _extreme red_: a ray which can only be discovered when the eye
is protected from the glare of the other rays by a cobalt blue glass,
is of a crimson character--a mixture of the _red_ and the _blue_, red
predominating.[96]

2. The _red_: the first ray visible under ordinary circumstances.

3. The _orange_: red passing into and combining with yellow.

4. The _yellow_: the most intensely luminous of the rays.

5. The _green_: the yellow passing into and blending with the blue.

6. The _blue_: in which the light very rapidly diminishes.

7. The _indigo_: the dark intensity of blue.

8. The _violet_: the _blue_ mingled again with the _red_--blue being in
excess.

9. The _lavender grey_: a neutral tint, produced by the combination of
the red, blue, and yellow rays, which is discovered most easily when
the spectrum is thrown upon a sheet of turmeric paper.

10. The fluorescent rays: which are either a _pure silvery blue_ or a
delicate _green_.

Newton regarded the spectrum as consisting of seven colours of
definite and unvarying refrangibility. Brewster and others appear to
have detected a great diffusion of the colours over the spectrum,
and regard white light as consisting only of three rays, which in the
prismatic images overlap each other; and from these--red, yellow,
and blue--all the others can be formed by combination in varying
proportions. The truth will probably be found to be, that the ordinary
prismatic spectrum is a compound of two spectra:--that is, as we have
the ordinary rainbow, and a supplementary bow, the colours of which are
inverted, so the extraordinary may be somewhat masked by the intense
light of the ordinary spectrum; and yet by overlapping produce the
variations of colour in the rays. We have already examined the heating
power found in these  bands, which, although shown to be in a
remarkable manner in constant agreement with the colour of a particular
ray, is not directly connected with it; that is, not as the effect of a
cause, or the contrary. The chemical action of the solar rays, to which
from its important bearings we shall devote a separate chapter, has, in
like manner with heat, been confounded with the sun’s luminous power;
but although associated with light and heat, and modified by their
presence, it must be distinguished from them.

We find the maximum of heat at one end of the spectrum, and that of
chemical excitation at the other--luminous power observing a mean point
between them. Without doubt we have these powers acting reciprocally,
modifying all the phenomena of each other, and thus giving rise to the
difficulties which beset the inquirer on every side.

We have beautiful natural illustrations of luminous refraction in
the rainbow and in the halo: in both cases the rays of light being
separated by the refractive power of the falling rain drop, or the
vesicles which form the moisture constituting a fog. In the simple toy
of the child--the soap-bubble floating upon the air--the philosopher
finds subjects for his contemplation; and from the unrivalled play of
colours which he discovers in that attenuated film, he learns that the
varying thicknesses of surfaces influence, in a most remarkable manner,
the colours of the sunbeam. Films of oil floating upon water present
similar appearances; and the colours developed in tempering steel
are due entirely to the thickness of the oxidized surface produced
by heat. There have lately been introduced some beautiful specimens
of paper rendered richly iridescent by the following process:--A
solution of a gum resin in chloroform is floated upon water, where
it forms a film giving all the colours of Newton’s rings. A sheet of
paper which has been previously sunk in the water is carefully lifted,
and the film thus removed adheres with great firmness to the paper,
and produces this rich and curious play of colour. The rich tints
upon mother-of-pearl, in the feathers of many birds, the rings seen
in the cracks of rock-crystal, or between the unequal faces of two
pieces of glass, and produced by many chemical and indeed mechanical
operations--are all owing to the same cause;--the refraction of the
luminous pencil by the condition of the film or surface. If we take
one of those steel ornaments which are formed by being covered with
an immense number of fine lines, it will be evident that these striæ
present many different angles of reflection, and that, consequently,
the rays thrown back will, at some point or another, have a tendency
to cross each other. The result of this is, that the quantity of
light is augmented at some points of intersection, and annihilated at
others.[97] Out of the investigation of the phenomena of diffraction,
of the effects of thin and thick plates upon light, and the results of
interference, has arisen the discovery of one of the most remarkable
conditions within the range of physical science.

_Two bright lights may be made to produce darkness._--If two pencils
of light radiate from two spots very close to each other in such a
manner that they cross each other at a given point, any object placed
at that line of interference will be illuminated with the sum of the
two luminous pencils. If we suppose those rays to move in waves, and
the elevation of the wave to represent the maximum of luminous effect,
then the two waves meeting, when they are both at the height of their
undulation, will necessarily produce a spot of greater intensity. If
now we so arrange the points of radiation, that the systems of luminous
waves proceed irregularly, and that one arrives at the screen half an
undulation before the other, the one in elevation falling into the
depression of the other, a mutual annihilation is the consequence. This
fact, paradoxical as it may appear, was broadly stated by Grimaldi,
in the description of his experiments on the inflection of light, and
has been observed by many others. The vibratory hypothesis, seizing
upon the analogy presented by two systems of waves in water, explains
this plausibly, and many similar phenomena of what is called the
_interference of light_; but still upon examination it does not appear
that the explanation is quite free from objection.[98]

Another theory, not altogether new to us, it being indicated in Mayer’s
hypothesis of three primary colours (1775), and to be found as a
problem in some of the Encyclopædias of the last century, has been put
forth, in a very original manner, by that master-mind of intellectual
Germany, Goethe; and from the very comprehensive views which this
poet-philosopher has taken of both animal and vegetable physiology
(views which have been adopted by some of the first naturalists of
Europe), we are bound to receive his theory of colours with every
respect and attention.

Goethe regards colour as the “thinning” of light; for example, by
obstructing a portion of white light, yellow is produced; by reducing
it still farther, red is supposed to result; and by yet farther
retarding the free passage of the beam, we procure a blue colour, which
is the next remove from blackness, or the absence of light. There is
truth in this; it bears about it a simplicity which will satisfy many
minds; by it many of the phenomena of colour may be explained: but it
is insufficient for any interpretation of several of those laws to
which the other theories do give us some insight.

Newton may have allowed himself to be misled by the analogy presented
between the seven rays of the spectrum and the notes in an octave.
The mystic number, seven, may have clung like a fibre of the web of
superstition to the cloak of the great philosopher; but the attack made
by Goethe upon the Newtonian philosophy betrays the melancholy fact of
his being diseased with the lamentable weakness of too many exalted
minds--an overweening self-esteem.

The polarization of light, as it has been unfortunately
called--unfortunately, as conveying an idea of determinate and
different points or poles, which only exists in hypothetical
analogy--presents to us a class of phenomena which promise to unclose
the mysterious doors of the molecular constitution of bodies.

This remarkable condition, as produced by the reflection of light from
glass at a particular angle, was first observed by Malus, in 1808,[99]
when amusing himself by looking at the beams of the setting sun,
reflected from the windows of the Luxembourg Palace through a double
refracting prism. He observed that when the prism was in one position,
the windows with their golden rays were visible; but that turned
round a quarter of a circle from that position, the reflected rays
disappeared although the windows were still seen.

The phenomenon of double refraction was noticed, in the first instance,
by Erasmus Bartholin, in Iceland-spar, a crystal the primary form of
which is a rhombohedron; who perceived that the two images produced by
this body were not in the same physical conditions.[100] It was also
studied by Huyghens and Sir Isaac Newton, and to our countryman we owe
the singular idea that a ray of light emerging from such a crystal
has _sides_. This breaking up of the beam of light into two,--which
is shown by looking through a pin-hole on a card through a crystal of
Iceland spar, when two holes become visible, is due to the different
states of tension in which the different layers constituting the
crystal exist.

In thus separating the ray of light into two rays, the condition
called polarisation has been produced, and by experiment we discover
that the single ray has properties different from those of the compound
or ordinary ray.

It is somewhat difficult to explain what is meant by, and what are the
conditions of, _polarised light_. In the first instance let us see by
what methods this peculiar state may be brought about.

If we reflect a ray of light from the surface of any body, fluid or
solid, but not metallic, at an angle between 53° and 68° it undergoes
what has been called _plane polarisation_. It may also be produced by
the refraction of light from several refracting surfaces acting upon
the pencil of light in succession; as by a bundle of plates of glass.
Each surface polarises a portion of the pencil, and the number of
plates necessary to polarise a whole beam depends upon the intensity of
the beam and the angle of incidence. Thus, the light of a wax candle
is wholly polarised by forty-seven plates of glass at an angle of 40°
41'; while at an angle of 79° 11' it is polarised by eight plates.
Again, plane polarisation may be produced by the double refraction of
crystals. Each of the two pencils is polarised, like light reflected
from glass at an angle of 56° 45', but in opposite planes.

Non-scientific readers will still ask,--What is this mysterious
condition of light which is produced by reflection and refraction at
peculiar angles to the incident ray. It is one of the most difficult of
problems to express in popular language. The conditions are, however,
these:--

An ordinary ray of light will be reflected from a reflecting surface at
whatever angle that surface may be placed in relation to the incident
beam.

A polarised ray of light is not reflected in all positions of the
reflecting surface.

An ordinary ray of light is freely transmitted through a transparent
medium, as glass, in whatever position it may be placed relative to the
source of light.

A polarised ray of light is not transmitted in all the positions of the
permeable medium.

Supposing a plate of glass is presented at the angle 56° to a polarised
ray, and the plane of incidence or reflexion is at right angles to the
plane of polarisation of the ray, _no light is reflected_. If we turn
the plate of glass round through 90°, when the plane of reflexion is
parallel to that of polarisation _the light is reflected_. If we turn
the plate round another 90°, so that the plane of reflexion and of
polarisation are parallel to each other, again _no light is reflected_;
and if we turn it through another 90° the reflection of the ray again
takes place.

Precisely the same result takes place when, instead of being reflected,
the polarised ray is transmitted.

Some substances have peculiar polarizing powers: _the tourmaline_ is a
familiar example. If a slice of tourmaline is taken, and we look at a
common pencil of light through it, we see it in whatever position we
may place the transparent medium. If, however, we look at a pencil of
polarised light, and turn the crystal round, it will be found that in
two positions the light is stopped, and that in two other positions it
passes freely through it to the eye.

By way of endeavouring to conceive something of what may be the
conditions which determine this very mysterious state, let us suppose
each ray of light to vibrate in two planes at right angles to each
other: one wave being vertical and the other horizontal. We have many
examples of this compound motion. The mast of a ship, by the force with
which she is urged through the water, describes a vertical wave, while
by the roll of the billows across which she sails, a lateral undulation
is produced at the same time. We may sometimes observe the same thing
when a field of corn is agitated by a shifting wind on a gusty day.

The hypothesis therefore is, that every ray of ordinary light consists
of two rays vibrating in different planes; and that these rays,
separated one from the other, have the physical conditions which we
call _polarized_.

The most transparent bodies may be regarded as being made up of atoms
arranged in certain planes. Suppose the plane of lamination of any
substance to be vertical in position, it would appear that the ray
which has a vertical motion passes it freely, whereas if we turn the
body round so that the planes of lamination are at right angles to the
plane of vibration of the ray, it cannot pass.

That some action similar to that which it is here endeavoured to
express in popular language does take place, is proved by the
correctness of the results deduced by rigid mathematical analyses
founded on this hypothesis.

There are two other conditions of the polarization of light--called
_circular_ and _elliptical_ polarization. The first is produced by
light when it is twice reflected from the second surface of bodies at
their angle of maximum polarization, and the second by reflexions from
the surfaces of metals at angles varying from 70° 45' to 78° 30'. The
motion of the wave in the first is supposed to be circular, or to be
that which is represented by looking along the centre of a corkscrew
as it is turned round. At every turn of the medium effecting _circular
polarization_ the colour of the ray of light is changed after a uniform
order. If turned in one direction, they change through red, orange,
yellow, green, and violet; and if in the other direction, the colours
appear in the contrary order.

The variety of striking effects produced by the polarization of light;
the unexpected results which have sprung from the investigation of the
laws by which it is regulated; and the singular beauty of many of its
phenomena, have made it one of the most attractive subjects of modern
science.

Ordinary light passes through transparent bodies without producing any
very striking effects in its passage; but this _extraordinary_ beam
of light has the power of insinuating itself between the molecules
of bodies, and by illuminating them, and giving them every variety
of prismatic hue, of enabling the eye to detect something of the
structure of the mass. The chromatic phenomena of polarized light are
so striking, that no description can convey an adequate idea of their
character.

Spectra more beautiful and intense than the prismatic image,--systems
of rings far excelling those of thin plates,--and forms of the most
symmetric order, are constantly presenting themselves, as the polarized
ray is passed through various transparent substances; the path of the
ray indicating whether the crystal has been formed round a single
nucleus or axis, or whether it has been produced by aggregation
around two axes. The  rings, and the dark or luminous crosses
which distinguish the path of the polarized ray, are respectively
due to different states of tension amongst the particles, although
those differences are so slight, that no other means is of sufficient
delicacy to detect the variation.

The poetry which surrounds these, in every way, mysterious conditions
of the solar beam, is such, that it is with difficulty that imagination
is restrained by the stern features of truth. The uses of this peculiar
property in great natural phenomena are not yet made known to us; but,
since we find on every side of us the natural conditions for thus
separating the beam of light, and effecting its polarization, there
must certainly be some most important end for which it is designed by
Him who said, “Let there be Light.”

It must not be forgotten that we have at command the means of showing
that the chromatic phenomena of polarized light are due to atomic
arrangement. By altering the molecular arrangement of transparent
bodies, either by heat or by mere mechanical pressure, the unequal
tension or strain of the particles is at once indicated by means of
the polarized ray of light and its rings of colour. Differences in the
chemical constitution of bodies, too slight to be discovered by any
other mode of analysis, can be most readily and certainly detected by
this luminous investigator of the molecular forces.[101]

Although we cannot enter into an examination of all the conditions
involved in the polarization of, and the action of matter on, ordinary
light, it will be readily conceived, from what has been already stated,
that some most important properties are indicated, beyond those which
science has made known.

Almost every substance in nature, in some definite position, appears
to have the power of producing this change upon the solar ray, as
may be satisfactorily shown by examining them with a polarizing
apparatus.[102] The sky at all times furnishes polarized light, which
is most intense where it is blue and unclouded, and the point of
maximum polarization is varied according to the relative position of
the sun and the observer. A knowledge of this fact has led to the
construction of a “Solar Clock,”[103] with which the hour can be
readily determined by examining the polarized condition of the sky.
It has been stated, that chemical change on the Daguerreotype plates
and on photographic papers is more readily produced by the polarized
than by the ordinary sunbeam.[104] If this fact be established by
future investigations, we advance a step towards the discovery so much
desiderated of the part it plays in natural operations.

The refined and accurate investigations of Dr. Faraday stand
prominently forward amid those which will redeem the present age from
the charge of being superficial, and they will, through all time, be
referred to as illustrious examples of the influence of a love of truth
for truth’s sake, in entire independence of the marketable value, which
it has been unfortunately too much the fashion to regard. The searching
examination made by this “interpreter of nature” into the phenomena
of electricity in all its forms, has led him onward to trace what
connexion, if any, existed between this great natural agent and the
luminous principle.

By employing that subtile analyzer, a polarized ray, Dr. Faraday
has been enabled to detect and exhibit effects of a most startling
character. He has proved magnetism to have the power of influencing a
ray of light in its passage through transparent bodies. A polarized ray
is passed through a piece of glass or a crystal, or along the length
of a tube filled with some transparent fluid, and the line of its path
carefully observed; if, when this is done, the solid or fluid body is
brought under powerful magnetic influence, such as we have at command
by making a very energetic voltaic current circulate around a bar of
soft iron, it will be found that the polarized light is disturbed;
that, indeed, it does not permeate the medium along the same line.[105]
This effect is most strikingly shown in bodies of the greatest density,
and diminished in fluids, the particles of which are easily moveable
over each other, and has not hitherto been observed in any gaseous
medium. The question, therefore, arises,--does magnetism act directly
upon the ray of light, or only indirectly, by producing a molecular
change in the body through which the ray is passing? This question,
so important in its bearings upon the connexion between the great
physical powers, will, no doubt, before long receive a satisfactory
reply. A medium is necessary to the production of the result, and, as
the density of the medium increases, the effect is enlarged: it would
therefore appear to be due to a disturbance by magnetic force of the
particles which constitute the medium employed.

Without any desire to generalize too hastily, we cannot but express
a feeling,--amounting to a certainty in our own mind,--that those
manifestations of luminous power, connected with the phenomena of
terrestrial magnetism, which are so evident in all the circumstances
attendant upon the exhibition of Aurora Borealis, and those luminous
clouds which are often seen, independent of the Northern Lights, that
a very intimate, relation exists between the solar radiations and that
power which so strangely gives polarity to this globe of ours.

In connexion with the mysterious subject of solar light, it is
important that we should occupy a brief space in these pages with the
phenomena of vision, which is so directly dependent upon luminous
radiation.

The human eye has been rightly called the “masterpiece of divine
mechanism;” its structure is complicated, yet all the adjustments of
its parts are as simple as they are perfect. The eye-ball consists of
four coats. The cornea is the transparent coat in front of the globe;
it is the first optical surface, and this is attached to the sclerotic
membrane, filling up the circular aperture in the white of the eye;
the choroid coat is a very delicate membrane, lining the sclerotic,
and covered with a perfectly black pigment on the inside; and close to
this lies the most delicately reticulated membrane, the retina, which
is, indeed, an extension of the optic nerve. These coats enclose three
humours,--the aqueous, the vitreous, and the crystalline humours.

The eye, in its more superficial mechanical arrangements, presents
exactly the same character as a camera obscura, the cornea and
crystalline lens receiving the images of objects refracting and
inverting them; but how infinitely more beautiful are all the
arrangements of the organ of vision than the dark chamber of Baptista
Porta![106] The humours of the eye are for the purpose of correcting
the aberrations of light, which are so evident in ordinary lenses,
and for giving to the whole an achromatic character. Both spherical
and chromatic aberration are corrected, the latter not entirely, and
by the agency of the cornea and the crystalline lens perfect images
are depicted on the retina, in a similar way to those very charming
pictures which present themselves in the table of the camera obscura.

The seat of vision has been generally supposed to be the retina;
but Mariotte has shown that the base of the optic nerve, which is
immediately connected with the retina, is incapable of conveying an
impression to the brain. The choroid coat, which lies immediately
behind the retina, is regarded by Mariotte and Bernoulli as the more
probable seat of vision. The retina, being transparent, offers no
obstruction to the passage of the light onward to the black surface of
the choroid coat, from which the vibrations are, in all probability,
communicated to the retina and conveyed to the brain. Howbeit, upon one
or the other of these delicate coats a distinct image is impressed
by light, and the communication made with the brain possibly by a
vibratory action. We may trace up the phenomena of vision to this
point; we may conceive undulations of light, differing in velocity and
length of wave, occasioning corresponding tremors in the neuralgic
system of the eye; but how these vibrations are to communicate
correct impressions of length, breadth, and thickness, no one has yet
undertaken to explain.

It has, however, been justly said by Herschel:--

“It is the boast of science to have been able to trace so far the
refined contrivances of this most admirable organ, not its shame to
find something still concealed from scrutiny; for, however anatomists
may differ on points of structure, or physiologists dispute on modes
of action, there is that in what we _do_ understand of the formation
of the eye, so similar, and yet so infinitely superior to a product
of human ingenuity; such thought, such care, such refinement, such
advantage taken of the properties of natural agents used as mere
instruments for accomplishing a given end, as force upon us a
conviction of deliberate choice and premeditated design, more strongly,
perhaps, than any single contrivance to be found whether in art or
nature, and renders its study an object of the greatest interest.”[107]

Has the reader ever asked himself why it is, having two eyes, and
consequently two pictures produced upon the tablets of vision, that we
see only one object? According to the law of visible direction, all the
rays passing through the crystalline lenses converge to one point upon
the retina,--and as the two images are coincident and nearly identical,
they can only produce the sensation of one upon the brain.

When we look at any round object, as the ornamented moderator lamp
before us, first with one eye, and then with the other, we discover
that, with the right eye, we see most of the right-hand side of the
lamp, and with the left eye more of the left-hand side. These two
images are combined, and we see an object which we know to be round.

This is illustrated in a most interesting manner by the little optical
instrument, _the Stereoscope_. It consists either of two mirrors placed
each at an angle of 45°, or of two semi-lenses turned with their curved
sides towards each other. To view its phenomena, two pictures are
obtained by the camera obscura on photographic paper of any object in
two positions, corresponding with the conditions of viewing it with the
two eyes. By the mirrors or the lenses these dissimilar pictures are
combined within the eye, and the vision of an actually solid object is
produced from the pictures represented on a plane surface. Hence the
name of the instrument; which signifies, _Solid I see_.

Analogy is often of great value in indicating the direction in which to
seek for a truth; but analogical evidence, unless where the resemblance
is very striking, should be received with caution. Mankind are so ready
to leap to conclusions without the labour necessary for a faithful
elucidation of the truth, that too often a few points of resemblance
are seized upon, and an inference is drawn which is calculated to
mislead.

There is an idea that the phenomena of sound bear a relation to those
of light,--that there exists a resemblance between the chromatic
and the diatonic scales. Sound, we know, is conveyed by the beating
of material particles--the air--upon the auditory membrane of the
ear, which have been set in motion by some distant disturbance of
the medium through which it passes. Light has been supposed to act
on the optic nerve in the same manner. If we imagine colour to be
the result of vibrations of different velocities and lengths, we can
understand that under some of these tremors, first established on the
nerves, and through them conveyed to the brain, sensations of pain
or pleasure may result, in the same way as sharp or subdued sounds
are disagreeable or otherwise. Intensely  bodies do make an
impression upon perfectly blind men; and those who, being born blind,
know no condition of light or colour, will point out a difference
between strongly illuminated red and yellow media. When the eyes are
closed we are sensible to luminous influence, and even to differences
of colour. We must consequently infer that light produces some peculiar
action upon the system of nerves in general; this may or may not
be independent of the chemical agency of the solar radiations; but
certainly the excitement is not owing to any calorific influence. The
system of nerves in the eye is more delicately organized, and of course
peculiarly adapted to all the necessities of vision.

Thus far some analogy does appear to exist between light and sound;
but the phenomena of the one are so much more refined than those of
the other--the impressions being all of them of a far more complicated
character, that we must not be led too far by the analogical evidence
in referring light, like sound, to mere material motion.

It was a beautiful idea that real impressions of external objects
are made upon the seat of vision, and that they are viewed, as in a
picture, by something behind the screen,--that these pictures become
dormant, but are capable of being revived by the operations of the mind
in peculiar conditions; but we can only regard it as a philosophical
speculation of a poetic character, the truth or falsehood of which we
are never likely to be enabled to establish.[108]

That which sees will never itself be visible. The secret principle
of sensation,--the mystery of the life that is in us,--will never be
unfolded to finite minds.

Numerous experiments have been made from time to time on the influence
of light upon animal life. It has been proved that the excitement of
the solar rays is too great for the healthful growth of young animals;
but, at the same time, it appears probable that the development of
the functional organs of animals requires, in some way, the influence
of the solar rays. This might, indeed, have been inferred from the
discovery that animal life ceases in situations from which light is
absolutely excluded. The instance of the Proteus of the Illyrian lakes
may appear against this conclusion. This remarkable creature is found
in the deep and dark recesses of the calcareous rocks of Adelsburg, at
Sittich; and it is stated, also in Sicily, and in the Mammoth caves
of Kentucky. Sir Humphry Davy describes the Proteus anguinus as “an
animal to whom the presence of light is not essential, and who can
live indifferently in air and in water, on the surface of the rock,
or in the depths of the mud.” The geological character of rocks,
however, renders it extremely probable that these animals may have
descended with the water, percolating through fissures from very near
the surface of the ground. All the facts with which science has made us
acquainted--and both natural and physical science has been labouring
with most untiring industry in the pursuit of truth--go to prove
that light is absolutely necessary to organization. It is possible
the influence of the solar radiations may extend beyond the powers
of the human senses to detect luminous or thermic action, and that
consequently a development of animal and vegetable forms may occur
where the human eye can detect no light; and under such conditions
the Proteus may be produced in its cavernous abodes, and also those
creatures which live buried deep in mud. Some further consideration of
the probable agency of light will occupy us, when we come to examine
the phenomena of vital forces.

Light is essentially necessary to vegetable life; and to it science
refers the powers which the plant possesses of separating carbon from
the air breathed by the leaves, and secreting it within its tissues for
the purpose of adding to its woody structure. As, however, we have, in
the growing plant, the action of several physical powers exerted to
different ends at the same time, the remarkable facts which connect
themselves with vegetable chemistry and physiology are deferred for a
separate examination.

The power of the solar rays to produce in bodies that peculiar gleaming
light which we call phosphorescence, and the curious conditions under
which this phenomenon is sometimes apparent, independent of the sun’s
direct influence, present a very remarkable chapter in the science of
luminous powers.

The phosphorescence of animals is amongst the most surprising of
nature’s phenomena, and it is not the less so from our almost entire
ignorance of the cause of it. Many very poetical fancies have been
applied in description of these luminous creations; and imagination
has found reason why they should be gifted with these extraordinary
powers. The glow-worm lights her lamp to lure her lover to her bower,
and the luminous animalcules of the ocean are employed in lighting up
the fathomless depths where the sun’s rays cannot penetrate, to aid its
monsters in their search for prey. “The lamp of love--the pharos--the
telegraph of the night,--which scintillates and marks, in the silence
of darkness, the spot appointed for the lover’s rendezvous,”[109] is
but a pretty fiction; for the glow-worm shines in its infant state,
in that of the larva, and when in its aurelian condition. Of the
dark depths of the ocean it may be safely affirmed that no organized
creation lives or moves in its grave-like silence to require this
fairy aid. Fiction has frequently borrowed her creations from science.
In these cases science appears to have made free with the rights of
fiction.

The glow-worms (_lampyris noctiluca_), it is well known, have the
power of emitting from their bodies a beautiful pale bluish-white
light, shining during the hours of night in the hedge-row, like crystal
spheres. It appears, from the observations of naturalists, that these
insects never exhibit their light without some motion of the body or
legs;--from this it would seem that the phosphorescence was dependent
upon nervous action, regulated at pleasure by the insect; for they
certainly have the power of obscuring it entirely. If the glow-worm is
crushed, and the hands or face are rubbed with it, luminous streaks,
similar to those produced by phosphorus, appear. They shine with
greatly increased brilliancy in oxygen gas and in nitrous oxide. From
these facts may we not infer that the process by which this luminosity
is produced, whatever it may be, has a strong resemblance to that of
respiration?

There are several varieties of flies, and three species of beetles of
the genus _Elater_, which have the power of emitting luminous rays.
The great lantern-fly of South America is one of the most brilliant, a
single insect giving sufficient light to enable a person to read. In
Surinam a very numerous class of these insects are found, which often
illuminate the air in a remarkable manner. In some of the bogs of
Ireland a worm exists which gives out a bright green light; and there
are many other kinds of creatures which, under certain circumstances,
become luminous in the dark. This is always dependent upon vitality;
for all these animals, when deprived of life, cease to shine.

At the same time we have many very curious instances of phosphorescence
in dead animal and vegetable matter; the lobster among the Crustacea,
and the whiting among fishes, are striking examples; decayed wood
also emits much light under certain conditions of the atmosphere.
This development of light does not appear to be at all dependent upon
putrefaction; indeed, as this process progresses, the luminosity
diminishes. We cannot but imagine that this light is owing, in the
first place, to direct absorption by, and fixation within, the
corpuscular structure of those bodies, and that it is developed by the
decomposition of the particles under the influence of our oxygenous
atmosphere.

The pale light emitted by phosphorus in the dark is well known; and
this is evidently only a species of slow combustion, a combination of
the phosphorus with the oxygen of the air. Where there is no oxygen,
phosphorus will not shine; its combustion in chlorine or iodine vapour
is a phenomenon of a totally different character from that which we are
now considering. This phosphorescence of animal and vegetable matter
has been regarded as something different from the slow combustion of
phosphorus; but, upon examination, all the chemical conditions are
found to be the same, and it is certainly due to a similar chemical
change.

The luminous matter of the dead whiting or the mackerel may be
separated by a solution of common salt or of sulphate of magnesia; by
concentrating these solutions the light disappears; but it is again
emitted when the fluid is diluted. The entire subject is, however,
involved in the mystery of ignorance, although it is a matter quite
within the scope of any industrious observer. The self-emitted light
of the carbuncle of the romancer is realized in these remarkable
phenomena.

The phosphorescence of some plants and flowers is not, perhaps, of
the same order as that which belongs to either of the conditions we
have been considering. It appears to be due rather to an absorption of
light and its subsequent liberation. If a nasturtium is plucked during
sunshine, and carried into a dark room, the eye, after it has reposed
for a short time, will discover the flower by a light emitted from its
leaves.

The following remarkable example, and an explanation of it by the poet
Goethe, is instructive:--

“On the 19th of June, 1799, late in the evening, when the twilight was
deepening into a clear night, as I was walking up and down the garden
with a friend, we very distinctly observed a flame-like appearance
near the oriental poppy, the flowers of which are remarkable for their
powerful red colour. We approached the place, and looked attentively
at the flowers, but could perceive nothing further, till at last, by
passing and repassing repeatedly, while we looked side-ways on them, we
succeeded in renewing the appearance as often as we pleased. It proved
to be a physiological phenomenon, and the apparent corruscation was
nothing but the spectrum of the flower in the complementary blue-green
colour. The twilight accounts for the eye being in a perfect state
of repose, and thus very susceptible, and the colour of the poppy is
sufficiently powerful in the summer twilight of the longest days to act
with full effect, and produce a complementary image.”[110]

The leaves of the _œnothera macrocarpa_ are said to exhibit phosphoric
light when the air is highly charged with electricity. The agarics
of the olive-grounds of Montpelier have been observed to be luminous
at night; but they are said to exhibit no light, even in darkness,
_during the day_. The subterranean passages of the coal mines near
Dresden are illuminated by the phosphorescent light of the _rhizomorpha
phosphoreus_, a peculiar fungus. On the leaves of the Pindoba palm, a
species of agaric grows which is exceedingly luminous at night; and
many varieties of the lichens, creeping along the roofs of caverns,
lend to them an air of enchantment by the soft and clear light which
they diffuse. In a small cave near Penryn, a luminous moss is abundant;
and it is also found in the mines of Hesse. According to Heinzmann, the
_rhizomorpha subterranea_ and _aidulæ_ are also phosphorescent.

It is but lately that a plant which abounds in the jungles in the
Madura district of the East Indies was sent to this country, which,
although dead, was remarkably phosphorescent; and, when in the
living state, the light which it emitted was extraordinarily vivid,
illuminating the ground for some distance. Those remarkable effects
may be due, in some cases, to the separation of phosphuretted hydrogen
from decomposing matter, and, in others, to some peculiar electric
manifestation.

The phosphorescence of the sea, or that condition called by fishermen
_brimy_, when the surface, being struck by an oar, or the paddle-wheels
of a steamer, gives out large quantities of light, has been attributed
to the presence of myriads of minute insects which have the power
of emitting light when irritated. The night-shining nereis (_Nereis
noctiluca_) emits a light of great brilliancy, as do several kinds of
the mollusca. The nereides attach themselves to the scales of fishes,
and thus frequently render them exceedingly luminous. Some of the
crustaceæ possess the same remarkable property;--twelve different
species of _cancer_ were taken up by the naturalists of the Zaire
in the Gulf of Guinea.[111] The _cancer fulgens_, discovered by Sir
Joseph Banks, is enabled to illuminate its whole body, and emits
vivid flashes of light. Many of the medusæ also exhibit powerful
phosphorescence.[112] These noctilucous creatures are, many of them,
exceedingly minute, several thousands being found in a tea-cup of sea
water. They float near the surface in countless myriads, and when
disturbed they give out brilliant scintillations, often leaving a train
of light behind them.[113] By microscopic examination no other fact has
been elicited than that these minute beings contain a fluid which, when
squeezed out, leaves a line of light upon the surface of water. The
appearance of these creatures is almost invariably on the eve of some
change of weather, which would lead us to suppose that their luminous
phenomena must be connected with electrical excitation; and of this,
the investigations of Mr. C. Peach, of Fowey, communicated to the
British Association at Birmingham, furnish the most satisfactory proofs
we have as yet obtained.

Benvenuto Cellini gave a curious account of a carbuncle which shone
with great brilliancy in the dark.[114] The same thing has been stated
of the diamond; but it appears to be necessary to procure these
emissions of light, that the minerals should be first warmed near a
fire. From this it may be inferred that the luminous appearance is
of a similar character to that of fluor spar, and of numerous other
earthy minerals, which, when exposed to heat, phosphoresce with great
brilliancy. Phosphorescent glow can also be excited in similar bodies
by electricity, as was first pointed out by Father Beccaria, and
confirmed by Mr. Pearsall.[115] These effects, it must be remembered,
are distinct from the electric spark manifested upon breaking white
sugar in the dark, or scratching sulphuret of zinc.

In the instances adduced there is not necessarily any exposure to the
sunshine required. It is probable that two, if not three, distinct
phenomena are concerned in the cases above quoted, and that all of them
are distinct from animal phosphorescence, or the luminous appearance
of vegetables. They, however, certainly prove, either that light is
capable of becoming latent, or that it is only a condition of matter,
in which it may be made manifest by any disturbance of the molecular
forces. We have, in answer to this, very distinct evidence that
some bodies do derive this property from the solar rays. Canton’s
phosphorus, which is a sulphuret of calcium, will, having been exposed
to the sun, continue luminous for some time after it is carried into
the dark; as will also the Bolognian stone,--a sulphuret of barium.
This result appears to be due to a particular class of the solar rays;
for it has been found, if these sulphurets, spread smoothly on paper,
are exposed to the influence of the solar spectrum for some little
time, and then examined in the dark, that luminous spaces appear,
exactly corresponding with the most refrangible rays, or those which
excite chemical change; and one very remarkable fact must not be
forgotten--the dark rays of the spectrum beyond the violet produce a
lively phosphorescence, which is _extinguished_ by the action of the
rays of least refrangibility, or the heat rays--whilst artificial heat,
such as a warm iron, produces a very considerable elevation of the
phosphorescent effect.[116] It is not improbable, that the fluorescent
rays of Mr. Stokes may be materially concerned in producing the
phenomena of phosphorescence: experiments are, however, required to
prove this.

In these allied phenomena we have effects which are evidently dependent
upon several dissimilar causes. The phosphorescence of the living
animal is due, without doubt, to nervous excitation: that of the living
vegetable to solar luminous influence; and in the case of the mosses of
caverns, &c. to the chemical agency of the sun’s rays, which appears to
be capable of conduction. In the dead organic matter we have a purely
chemical action developing the light, and in the inorganic bodies we
have peculiar molecular constitution, by which an absorption of light
appears to take place.

The subject is one of the greatest difficulty; the torch of science
is too dim to enable us to see the causes at work in producing these
marvellous effects. The investigation leads, to a certain extent, to
the elucidation of many of the secrets of luminous action; and the
determination of the question, whether light is an emanation from the
sun, or only a subtile principle diffused through all matter, which is
excited by solar influence, is intimately connected with the inquiry.

It has been stated that matter is necessary to the development of
light; that no luminous effect would be produced if it were not for
the presence of matter. Of this we not only have no proof, but such
evidence as we have is against the position. There is no loss of light
in the most perfect vacuum we can produce by any artificial means,
which should be the case if matter was concerned in the phenomena of
light, as a cause.

Colour is certainly a property regulated by material bodies; or
rather, the presence of matter is necessary to the production of
colour. Chlorine gas is a pale yellow, and nitrous vapour a yellowish
red. These and one or two other vapours, which are near the point of
condensation into fluids, are the only  gaseous or vaporiform
bodies. The sky is blue, because the material particles of the
atmosphere reflect back the blue rays. But we have more practical
illustrations than this. The flame of hydrogen burning with oxygen
gives scarcely any light; allow it to impinge on lime, a portion of
which is carried off by the heat of the flame, and the most intense
artificial light with which we are acquainted is produced. Hydrogen gas
alone gives a flame in which nearly all but the blue rays are wanting:
place a brush of steel or asbestos in it, and many of the other rays
are at once produced. An argand lamp, and more particularly the lamp
in which camphine--a purified turpentine,--is burnt, gives a flame
which emits most of the rays found in sunlight. Spirit of wine mixed
with water, warmed and ignited, gives only yellow rays; add nitrate
of strontian and they become red; but nitrate of barytes being mixed
with the fluid, they are changed to green and yellow; salts of copper
afford fine blue rays, and common salt intense yellow ones. Many of
these  rays and others can be produced in great power by the
use of various solid bodies introduced into flame. This has not been
sufficiently pointed out by authors; but it is clear from experiments
that light requires the presence of matter to enable it to diffuse its
 glories. How is it that the oxygen and hydrogen flame gives so
little light, and with a solid body present, pours forth such a flood
of brilliancy?

The production of artificial light by electrical and chemical agencies
will necessarily find some consideration under their respective
heads. There are numerous phenomena which connect themselves with
luminous power, or appear to do so, which, in the present state of
our knowledge, cannot come immediately under our attention. We are
compelled to reserve our limited space for those branches of science
which we are enabled to connect with the great natural operations
constantly going on around us. Many of these more abstruse results
will, however, receive some incidental notice when we come to examine
the operation of the combined physical forces on matter.

We see in light a principle which, if it has not its source in the
sun, is certainly dependent upon that luminary for its manifestations
and powers. From that “fountain of light” we find this principle
travelling to us at a speed which almost approaches the quickness of
thought itself; yet by the refinements of science we have been enabled
to measure its velocity with the utmost accuracy. The immortal poet of
our own land and language, in his creations of Ariel, that “tricksy
spirit,” who could creep like music upon the waters, and of the
fantastic Puck, who could girdle the earth in thirty minutes, appears
to have approached to the highest point to which mere imagination could
carry the human mind as to the powers of things ethereal. Science has,
since then, shown to man that this “spirit, fine spirit,” was a laggard
in his tasks, and a gross piece of matter, when compared with the
subtile essences which man, like a nobler Prospero, has now subdued to
do him service.

Light is necessary to life; the world was a dead chaos before its
creation, and mute disorder would again be the consequence of its
annihilation. Every charm which spreads itself over this rolling globe
is directly dependent upon luminous power. Colours, and probably,
forms, are the result of light; certainly the consequence of solar
radiations. We know much of the mysterious influences of this great
agent, but we know nothing of the principle itself. The solar beam has
been tortured through prismatic glasses and natural crystals; every
chemical agent has been tried upon it, every electrical force in the
most excited state brought to bear upon its operations, with a view
to the discovery of the most refined of earthly agencies; but it has
passed through every trial without revealing its secrets, and even the
effects which it produces in its path are unexplained problems, still
to tax the intellect of man.

Every animal and every plant alike proclaim that life and health are
due to light; and even the crystallizing forms of inorganic matter, by
bending towards it, confess its all-prevailing sway. From the sun to
each planet revolving around that orb, and to the remotest stars which
gleam through the vast immensity of heaven, we discover this power
still in its brightness, giving beauty and order to these unnumbered
creations; no less completely than to this small island of the universe
which we call our Earth. Through every form of matter we can mark
its power, and from all, we can, under certain conditions, evoke it
in lustre and activity. Over all and through all light spreads its
ethereal force, and manifests, in all its operations, powers which
might well exalt the mind of Plato to the idea of an omniscient and
omnipresent God. Science, with her Ithuriel wand, has, however, shown
that light is itself the effect of a yet more exalted cause, which we
cannot reach.

Indeed, the attentive study of the fine abstractions of science lifts
the mind from the grossness of matter, step by step, to the refinements
of immateriality, and there appear, shadowed out beyond the physical
forces which man can test and try, other powers still ascending, until
they reach the Source of every good and every perfect gift.


FOOTNOTES:

[84] “These--oxygen, hydrogen, nitrogen, and carbon--are the four
bodies, in fact, which, becoming animated at the fire of the sun,
the true torch of Prometheus, approve themselves upon the earth
the eternal agents of organisation, of sensation, of motion and of
thought.”--Dumas, _Leçons de Philosophie Chimique_, p. 100. Paris, 1837.

[85] It will be found in examining any of the works of the
alchemists,--particularly those of Geber, _De inveniendi arte Auri et
Argenti_, and his _De Alchemiâ_; Roger Bacon’s _Opus Majus, or Alchymia
Major_; Helvetius’ _Brief of the Golden Calf_; or Basil Valentine’s
_Currus Triumphalis_,--that in the processes of transmutation the solar
light was supposed to be marvellously effective. In Boyle’s _Sceptical
Chemist_ the same idea will be found pervading it.

Amid all their errors, the alchemists were assiduous workmen, and to
them we are indebted for numerous facts. Of them, and of their age, as
contrasted with our own, Gibbon remarks:--“Congenial to the avarice
of the human heart, it was studied in China, as in Europe, with equal
eagerness and equal success. The darkness of the middle ages ensured
a favourable reception to every tale of wonder; and the revival of
learning gave new vigour to hope, and suggested more specious arts
of deception. Philosophy, with the aid of experience, has at length
banished the study of alchemy; and the present age, however desirous of
riches, is content to seek them by the humbler means of commerce and
industry.”--_Decline and Fall_, vol. ii. p. 137.

[86] On the two theories the following maybe consulted:--Young,
_Supplement to Encyclopædia Britannica_, article _Chromatics_;
Fresnel, _Supplément à la Traduction Française de la 5ième édition du
Traité de Chimie de Thomson_, par Riffault, Paris, 1822; Herschel’s
Article, _Light_, in the Encyclopædia Metropolitana, and the French
Translation of it by Quetelet and Verhulst; Airy’s _Tract on the
Undulatory Theory_, in his Tracts, 2nd edition, Cambridge, 1831; Powel,
_The Undulatory Theory applied to Dispersion_, &c. p. 184; Lloyd’s
_Lectures_, Dublin, 1836-41; Cauchy, _Sur le Mouvement des Corps
élastiques_, Mémoires de l’Institut, 1827, vol. ix. p. 114; _Théorie de
la Lumière_, Ibid. vol. x. p. 293; M’Cullagh, _On Double Refraction_,
Ibid., vol. xvi.; _Geometrical Propositions applied to the Wave Theory
of Light_, Ibid., vol. xvii.; Sir David Brewster’s papers in the
Transactions of the Royal Society of Edinburgh, and the Philosophical
Magazine.

[87] _Results of Astronomical Observations made during the years
1834-38, at the Cape of Good Hope, &c._ By Sir John Herschel, Bart.,
K.H., D.C.L., F.R.S.--“In the contemplation of the infinite, in number
and in magnitude, the mind ever fails us. We stand appalled before this
mighty spectre of boundless space, and faltering reason sinks under the
load of its bursting conceptions. But, placed as we are on the great
locomotive of our system, destined surely to complete at least one
round of its ethereal course, and learning that we can make no apparent
advance on our sidereal journey, we pant with new ardour for that
distant bourne which we constantly approach without the possibility
of reaching it. In feeling this disappointment, and patiently bearing
it, let us endeavour to realise the great truth from which it flows.
It cannot occupy our mind without exalting and improving it.”--_Sir D.
Brewster_: North British Review.

[88] For examples of this, consult Graham’s _Elements of Chemistry_;
Brande’s _Manual of Chemistry_; or, indeed, any work treating of the
science. The formation of ink, by mixing two colourless solutions,
one of gallic acid and another of sulphate of iron, may be taken as a
familiar instance.

[89] Sir John Herschel, in his paper _On the Chemical Action of the
Rays of the Solar Spectrum on Preparations of Silver_, remarks that,
“it may seem too hazardous to look for the cause of this very singular
phenomenon in a real difference between the chemical agencies of those
rays which issue from the central portion of the sun’s disc, and those
which, emanating from its borders, have undergone the absorptive
action of a much greater depth of its atmosphere; and yet I confess
myself somewhat at a loss what other cause to assign for it. It must
suffice, however, to have thrown out the hint; remarking only, that
I have other, and, I am disposed to think, decisive evidence (which
will find its place elsewhere) of the existence of an absorptive solar
atmosphere, extending beyond the luminous one. The breadth of the
border, I should observe, is small, not exceeding 0·5 or 1/7 part of
the sun’s radius, and this, from the circumstances of the experiment,
must necessarily err in excess.”--Philosophical Transactions, 1840.

[90] _Experiments and Observations on some Cases of Lines in the
Prismatic Spectrum, produced by the passage of Light through 
Vapours and Gases, and from certain  Flames._ By W. A.
Miller, M.D., F.R.S., Professor of Chemistry in King’s College,
London.--Philosophical Magazine, vol. xxvii.

[91] _Report on the Mollusca and Radiata of the Ægean Sea, and on their
distribution, considered as bearing on Geology._ By Edward Forbes,
F.R.S., &c.--Reports of the British Association, vol. xii. Professor
Forbes remarks:--“A comparison of the testacea, and other animals of
the lowest zones, with those of the higher, exhibits a very great
distinction in the hues of the species, those of the depths being, for
the most part, white or colourless, while those of the higher regions,
in a great number of instances, exhibit brilliant combinations of
colour. The results of an enquiry into this subject are as follows:--

“The majority of shells of the lowest zone are white or transparent; if
tinted rose is the hue, a very few exhibit markings of another colour.
In the seventh region, white species are also very abundant, though
by no means forming a proportion so great as the eighth. Brownish
red, the prevalent hue of the brachiopoda, also gives a character
of colour to the fauna of this zone; the crustacea found in it are
red. In the sixth zone the colours become brighter, reds and yellows
prevailing,--generally, however, uniformly colouring the shell. In
the fifth region many species are banded or clouded with various
combinations of colours, and the number of white species has greatly
diminished. In the fourth, purple hues are frequent, and contrasts of
colour common. In the second and third, green and blue tints are met
with, sometimes very vivid; but the gayest combinations of colour are
seen in the littoral zone, as well as the most brilliant whites.

“The animals of Testacea, and the Radiata of the higher zones, are
much more brilliantly  than those of the lower, where they are
usually white, whatever the hue of the shell may be. Thus the genus
_Trochus_ is an example of a group of forms mostly presenting the
most brilliant hues both of shell and animal; but whilst the animals
of such species as inhabit the littoral zone are gaily chequered with
many vivid hues, those of the greater depth, though their shells are
almost as brightly covered as the coverings of their allies nearer the
surface, have their animals, for the most part, of a uniform yellow or
reddish hue, or else entirely white. The chief cause of this increase
of intensity of colour as we ascend is, doubtless, the increased amount
of light above a certain depth.”--p. 172.

[92] Ἁμὁρφωτα. _On the Epipolic Dispersion of Light_, being a paper
entitled, _On a case of Superficial Colour presented, by a homogeneous
liquid internally colourless_. By Sir J. F. W. Herschel, Bart, K.H.,
F.R.S., &c.--_An epipolized beam of light_ (meaning thereby a beam
which has once been transmitted through a quiniferous solution, and
undergone its dispersing action) _is incapable of further undergoing
epipolic dispersion_. In proof of this the following experiment may be
adduced,--

A glass jar being filled with a quiniferous solution, a piece of plate
glass was immersed in it vertically, so as to be entirely covered, and
to present one face directly to the incident light. In this situation,
when viewed by an eye almost perpendicularly over it, so as to graze
either surface very obliquely, neither the anterior nor posterior face
showed the slightest trace of epipolic colour. Now, the light, at its
egress from the immersed glass, entered the liquid under precisely the
same circumstances as that which, when traversing the anterior surface
of the glass jar, underwent epipolic dispersion on first entering
the liquid. It had, therefore, lost a property which it originally
possessed, and could not, therefore, be considered _qualitatively_ the
same light.--Philosophical Transactions, vol. cxxxvi.

[93] In connection with this view, the Newtonian theory should be
consulted, for which see--_A Letter of_ Mr. Isaac Newton, _Professor
of the Mathematicks in the University of Cambridge; containing his new
Theory about Light and Colors: sent by the Author to the Publisher,
from Cambridge, Feb. 6, 1671-72, in order to be communicated to the
Royal Society._

[94] In that admirable work, _The Physical Atlas_ of Dr. Berghaus, of
which a very complete edition by Alexander Keith Johnstone is published
in this country, the following order of the distribution of plants is
given:--

    1. The region of palms and bananas    Equatorial zone.
    2. Tree ferns and figs                Tropical zone.
    3. Myrtles and laurels                Sub-tropical zone.
    4. Evergreen trees                    Warm temperate zone.
    5. European trees                     Cold temperate zone.
    6. Pines                              Sub-arctic zone.
    7. Rhododendrons                      Arctic zone.
    8. Alpine plants                      Polar zone.

Consult Humboldt, _Essai sur la Géographie des Plantes_, Paris,
1807; _De Distributione Geographicâ Plantarum_, Paris, 1817. Schouw,
_Grundzüge der Pflanzengeographie_. Also his _Earth, Plants, and Man_;
translated by Henfrey, in _Bohn’s Scientific Library_. Lamouroux,
_Géographie Physique_. _The Plant, a Biography_: by Schleiden;
translated by Henfrey. _Physical Geography_: by Mrs. Somerville.

[95] Fraunhofer’s measure of illuminating power is as follows:--

    At the 22nd degree of the red       0·032
       "   34th degree of the red       0·094
       "   22nd degree of the orange    0·640
       "   10th degree of the yellow    1·000
       "   42nd degree of the yellow    0·480
       "   2nd degree of the blue       0·170
       "   16th degree of the indigo    0·031
       "   43rd degree of the violet    0·0056

[96] Herschel, _On the Action of Crystallized Bodies on Homogeneous
Light, and on the causes of the deviation from Newtons scale in
the tints which many of them develope on exposure to a polarized
ray_.--Phil. Trans., vol. cx., p. 88.

[97] _On the Nature of Light and Colours_: Lecture 39, in Young’s
_Lectures on Natural Philosophy_, Kelland’s Edition, p. 373, and the
authorities there quoted.

[98] Brewster’s _Optics_: Lardner’s Cabinet Cyclopædia. Herschel, _On
Light_: Encyclopædia Metropolitana.

[99] Malus, _Sur une Propriété de la Lumière Réfléchie_: Mémoires
d’Arcueil. Numerous memoirs by Sir David Brewster, in the Philosophical
Transactions.

[100] Bartholin, _On Iceland Crystals_: Copenhagen, 1669. _An
Accompt of sundry Experiments made and communicated by that Learn’d
Mathematician_ Dr. Erasmus Bartholin, _upon a Chrystal like Body sent
to him out of Island_: in connection with which Dr. Matthias Paissenius
writes:--The observations of the excellent Bartholin upon the Island
Chrystal are, indeed, considerable, as well as painful. We have here,
also, made some tryals of it upon a piece he presented me with, which
confirm his observations. Mean time he found it somewhat scissile and
reducible by a knife into thin laminas or plates, which, when single,
shew’d the object single, but laid upon one another shew’d it double;
the two images appearing the more distant from one another, the
greater the number was of those thin plates laid on one another. With
submission to better judgements I think it to be a kind of Selenites.
Some of our curious men here were of opinion that the Rhomboid figure
proper to this stone was the cause of the appearances doubled thereby.
But having tryed whether in other transparent bodies of the like figure
the like would happen, we found no such thing in them, which made us
suspect some peculiarity in the very Body of the stone.--Phil. Trans.
for 1670, vol. v.

[101] _On the Application of the Laws of Circular Polarization to the
Researches of Chemistry_: by M. Biot.--Nouvelles Annales du Muséum
d’Histoire Naturelle, vol. iii., and Scientific Memoirs, vol. i.
p. 600. _On Circular Polarization_: by Dr. Leeson.--Memoirs of the
Chemical Society.

[102] In Sir David Brewster’s Treatise _On Optics_, chap, xviii., _On
Polarization_, the best arrangements for a polarizing apparatus will be
found described.

[103] This beautiful application was recently made by Professor
Wheatstone, the particulars of which will be found in his interesting
communication.--_On a means of determining the apparent Solar Time
by the diurnal changes of the Plane of Polarization at the Northern
Pole of the Sky_: Report of the Eighteenth Meeting of the British
Association.

[104] _On the Polarization of the Chemical Rays of Light_: by John
Sutherland, M.D., in which the author refers to the following
experiment of M. J. E. Bérard--“I received the chemical rays directed
into the plane of the meridian on an unsilvered glass, under an
incidence of 35° 61'. The rays reflected by the first glass were
received upon a second, under the same incidence. I found that when
this was turned towards the south, the muriate of silver exposed to
the invisible rays which it reflected was darkened in less than half
an hour; whereas, when it was turned towards the west, the muriate
of silver exposed in the place where the rays ought to have been
reflected, was not darkened, although it was left exposed for two
hours. It is consequently to be presumed that the chemical rays can
undergo double refraction in traversing certain diaphanous bodies; and
lastly, we may say that they enjoy the same physical properties as
light in general.”--Philosophical Magazine, vol. xx.

Dr. Leeson has stated that Daguerreotype pictures can be taken more
readily under the influence of polarized light, than by ordinary
radiation.

[105] _On the Magnetization of Light, and the Illumination of Magnetic
Lines of Force_: by Michael Faraday, D.C.L., F.R.S.--Philosophical
Transactions, vol. cxxxvii.--The following remarks are to the point
of doubt referred to in the text.--“The magnetic forces do not act
on the ray of light directly and without the intervention of matter,
but through the mediation of the substance in which they and the ray
have a simultaneous existence; the substances and the forces giving to
and receiving from each other the power of acting on the light. This
is shown by the non-action of a vacuum, of air or gases, and it is
also further shown by the special degree in which different matters
possess the property. That magnetic force acts upon the ray of light
always with the same character of manner, and in the same direction,
independent of the different varieties of substance, or their states
of solid or liquid, or their specific rotative force, shows that
the magnetic force and the light have a direct relation; but that
substances are necessary, and that these act in different degrees,
shows that the magnetism and the light act on each other through the
intervention of the matter. Recognising or perceiving _matter_ only by
its powers, and knowing nothing of any imaginary nucleus abstract from
the idea of these powers, the phenomena described must strengthen my
inclination to trust in the views I have advanced in reference to its
nature.”--Phil. Mag. vol. xxiv.

[106] The invention of the camera obscura certainly belongs to
Giambattista Porta, and is described in his _Magiæ Naturalis, sive de
Miraculis Rerum Naturalium, Libri Viginti_; Antwerp, 1561. An English
translation made in 1658 exists, but I have not seen it.

Hooke, in one of the earliest volumes of the Philosophical
Transactions, describes as new many of the phenomena mentioned by
Porta, and particularly the images of the dark chamber.

[107] Herschel, _On Light_,--Encyclopædia Metropolitana.

[108] “I would here observe that a consideration of many such
phenomena (the obliteration and revival of photographic drawings) has
led me to regard it as not impossible that the retina itself may be
_photographically_ impressed by strong light, and that some at least
of the phenomena of visual spectra and secondary colours may arise
from the sensorial perception of actual changes in progress in the
physical state of that organ itself subsequent to the cessation of the
direct stimulant.”--_On the action of the Rays of the Solar Spectrum on
Vegetable Colours, &c._: by Sir J. F. W. Herschel, Bart.

[109] Dumeril.

[110] _Theory of Colours_: by Goethe; translated by Eastlake.

[111] See Tuckey’s Narrative of the Expedition of the Zaire.

[112] The most complete examination of this subject will be found in
two Memoirs:--

1. _Experiments and observations on the light which is spontaneously
emitted with some degree, of permanency from various bodies._--Phil.
Trans., vol. xc.

2. _A continuation of the above, with some experiments and observations
on solar light, when imbibed by Canton’s phosphorus_: by Nathaniel
Hulm, M.D.--Phil. Trans., vol. xci.; and in the _Monograph of the
British Naked-eyed Medusæ_, by Professor Edward Forbes (published
for the Ray Society). See Wilson’s note to the account of _Pennalata
phosphorea_ in Johnston’s Zoophytes, 2nd edition.

[113] _A General Outline of the Animal Kingdom_: by Thomas Rymer Jones,
F.L.S.--Acalephæ, p. 64. _Lettre à M. Dumas sur la Phosphorescence des
Vers luisants_: par M. Ch. Matteucci.--Annales de Chimie, vol. ix. p.
71, 1843.

[114] _Memoirs of Benvenuto Cellini--Bohn’s Standard Library._ See also
his Treatise on his Art as a Sculptor and Engraver. Florence, 1568. 4to.

[115] _Phosphorescence of the Diamond_: by M. Reiss (Revue Scientifique
et Industrielle, vol. xxiii. p. 185).--“The diamond, phosphorescent
by insulation, lost rapidly its phosphorescence when submitted to the
action of the red rays of the solar spectrum. On the contrary, the
blue rays are those which render the diamond the most luminous in
the dark. It is probable that the phosphorescence produced by heat
is equally diminished by the action of the red rays of the solar
spectrum.” Giovanni Battista Beccaria published his experiments in
1769. See Priestley’s _History of Electricity_; and _On the Effects
of Electricity upon Minerals which are Phosphorescent by Heat_; and
_Further Experiments on the communication of Phosphorescence and Colour
to bodies of Electricity_; by Thomas J. Pearsall.--Journal of the
Royal Institution of Great Britain, Oct. 1830, Feb. 1831.--These two
memoirs contain the most complete set of experiments on this subject
which have yet been made; see _Placidus Heinrich_, _Phosphorescenz
der Körper_, vol. iv.; Gmelin’s _Handbuch der Chemie_, part 1.;--_On
the Phosphorescence of Minerals_, Brewster: Edinburgh Philosophical
Journal, vol. i. p. 137.;--_The Aërial Noctiluca, or some New
Phenomena, and a process of a factitious self shining substance_:
Boyle’s Works, vol. iv.

[116] _Des Effets produits sur les corps par les Rayons Solaires_: par
M. Edmond Becquerel.--Annales de Chimie, vol. ix. p. 257. 1843.

M. Becquerel has applied the term _phosphorogénique_ to those rays
producing phosphorescence.




CHAPTER VIII.

ACTINISM--CHEMICAL RADIATIONS.

  The Sun-ray and its Powers--Darkening of Horn Silver--Niepce’s
    Discovery--Prismatic Spectrum--Refrangibility of Light, Heat, and
    Actinism--Daguerre’s Discovery--Photography--Chemical Effects
    produced by Solar Radiations--Absorption of Actinism--Phenomena of
    the Daguerreotype--Chemical Change produced upon all Bodies--Power
    of Matter to restore its Condition--Light protects from Chemical
    Change--Photographs taken in Darkness--Chemical Effects of Light
    on organized Forms--Chemical Effects of Solar Heat--Influence
    of Actinism on Electricity--Radiations in Darkness--Moser’s
    Discoveries, &c.


Heat and light are derived from the sun, and we have attempted to show,
not only that the phenomena of these two principles are different, but
that they can scarcely, in the present condition of our knowledge, be
regarded as modified manifestations of _one_ superior power. Associated
with these two remarkable elements, others may exist in the solar rays.
Electrical phenomena are certainly developed by both heat and light,
and peculiar electric changes are produced by exposure to sunshine.
Electricity may be merely _excited_ by the solar rays, or it may
_flow_ like light from the sun. Chemical action may be only due to the
disturbance of some diffused principle; or it may be directly owing to
some agency which is radiated at once from the sun.

A sun ray is a magical thing: we connect it in our fancy with the
most ethereal of possible creations. Yet in its action on matter it
produces colour; it separates the particles of solid masses farther
from each other, and it breaks up some of the strongest forces of
chemical affinity. To modern science is entirely due the knowledge
we have gained of the marvellous powers of the sunbeam; and it has
rendered us familiar with phenomena, to which the incantation scenes
of the Cornelius Agrippas of the dark ages were but ill-contrived
delusions, and their magic mirrors poor instruments. The silver tablets
of the photographic artist receiving fixed impressions of the objects
represented in the dark chamber by a lens, are far superior as examples
of natural magic.

In the dark ages, or rather as the earliest gleams of the bright
morning of inductive research were dispelling the mists of that
phantom-peopled period, it was observed, for the first time, that the
sun’s rays turned a white compound black. Man must have witnessed, long
before, that change which is constantly taking place in all vegetable
colours: some darkening by exposure to sunlight, while others were
bleached by its influence. Yet those phenomena excited no attention,
and the world knew nothing of the mighty changes which were constantly
taking place around them. The alchemists--sublime pictures of credulous
humanity--toiling in the smoke of their secret laboratories, waiting
and watching for every change which could be produced by fire, or by
their “royal waters,” caught the first faint ray of an opening truth;
and their wild fancy, that light could change silver into gold, if they
but succeeded in getting its subtile beams to interpenetrate the metal,
was the clue afforded to the empirical philosopher to guide him through
a more than Cretan labyrinth.[117]

The first fact recorded upon this, point was, that horn silver
blackened when exposed to the light. Without doubt many anxious
thoughts were given by these alchemists to that fact. Here was, as it
appeared, a mixing up of light and matter, and behold the striking
change! It was a step towards the realization of their dreams. Alas!
poor visionaries! in pursuing an ideality they lost the reality which
was within their grasp.

Truths come slowly upon man, and long it is before these angel visits
are acknowledged by humanity. The world clings to its errors, and
avoids the truth, lest its light should betray their miserable follies.

At length a man of genius announced that “_No substance can be
exposed to the sun’s rays without undergoing a chemical change_;”
but his words fell idly upon the ear. His friends looked upon his
light-produced pictures as singular; they preserved them in their
cabinets of curiosities; but the truths which he enunciated were soon
forgotten. Howbeit his words were recorded, and it is due to the
solitary experimentalist of Châlons on the Saône, to couple the name
of Niepce with the discovery of a fact which is scarcely second to
the development of the great law of universal gravitation.[118] But
an examination awaits us, which, for its novelty, has more charms
than most branches of science, and which, for the extensive views it
opens to the inquirer, has an interest in nowise inferior to any other
physical investigation.

The prismatic spectrum affords us the means of examining the conditions
of the solar rays with great facility. In bending the ray of white
light out of its path, by means of a triangular piece of glass, we
divide it in a remarkable manner. We learn that heat is less refracted
by the glass than the other powers; we find the maximum point of the
calorific rays but slightly thrown out of the right line, which the
solar pencil would have taken, had it not been interrupted by the
prism; and the thermic action is found to diminish with much regularity
on either side of this line. We discover that the luminous power is
subject to greater refraction, and that its maximum lies considerably
above that of heat; and that, in like manner, on each side the light
diminishes, producing orange, red, and crimson colours below the
maximum point, and green, blue, and violet above it. Again, we find
that the radiations which produce chemical change are more refrangible
than either of the others, and the maximum of this power is found
at the point where light rapidly diminishes, and where scarcely any
heat can be detected: it extends in full activity, above its maximum,
to a considerable distance, where no trace of light under ordinary
conditions exists, and below that point, until light, appearing to
act as an interfering agent, quenches its peculiar properties. These
are strong evidences that _light_ and _actinism_--as this principle
has been named--are not identical: and we may separate them most
easily and effectually from each other. Certain glasses, stained dark
blue, with oxide of cobalt, admit scarcely any light; but they offer
no interruption to the passage of actinism or the chemical rays; on
the contrary, a pure yellow glass, or a yellow fluid, which does not
sensibly reduce the intensity of any one colour of the chromatic band
of luminous rays, completely cuts off this chemical principle, whatever
it may be. In addition to these, there are other results which we shall
have to describe, which prove that, although associated in the solar
beam, light and actinism are in constant antagonism.

When Daguerre first published his great discovery, the European public
regarded his metal tablets with feelings of wonder: we have grown
accustomed to the beautiful phenomena of this art, and we have become
acquainted with a number of no less beautiful processes on paper,
all of which, if studied aright, must convince the most superficial
thinker, that a world of wonder lies a little beyond our knowledge,
but within the reach of industrious and patient research. Photography
is the name by which the art of sun-painting will be for ever known.
We regard this as unfortunate, conveying as it does a false idea,--the
pictures not being _light-drawn_. Could we adopt the name given
by Niepce to the process, the difficulty would be avoided, since
Heliography involves no hypothesis, and strictly tells the undeniable
truth, that our pictures are _sun-drawn_. That pictures can be produced
by the rays from artificial sources, presents no objection to this;
these rays were still originally derived from the sun.

By whatever name we determine to convey our ideas of these phenomena,
it is certain that they involve a series of effects which are of the
highest interest to every lover of nature, and of the utmost importance
to the artist and the amateur. By easy manipulation we are now enabled
to give permanence to the charming pictures which are produced by means
of that pleasing invention of Baptista Porta, the _Camera Obscura_. Any
image, which being refracted by the lens of this instrument falls upon
the table in its dark chamber, may be secured with its most delicate
gradations of shadows, upon either a metallic or a paper tablet.

But let us proceed to the examination of a few of the more striking
phenomena of these chemical changes. To commence with some of the more
simple but no less important results.

Chlorine and hydrogen will not unite in darkness, nor will chlorine and
carbonic oxide; but, if either of those gaseous mixtures is exposed to
sunshine, they combine rapidly, and often with explosion. A solution of
the sulphate of iron in ordinary water may be preserved for a long time
in the dark without undergoing any change; expose it to the sunshine,
and a precipitation of oxide of iron is very rapidly produced. The
mineral chameleon, the _manganesiate of potash_ in solution, is
almost instantly decomposed in daylight; but it is a long time before
it undergoes any change in darkness. The same thing occurs with a
combination of platinum and lime: indeed, it appears that precipitation
is at all times, and under all circumstances, accelerated by the solar
rays. As these precipitations are in exact agreement with the quantity
of actinic radiation to which the solutions have been exposed, we may
actually weigh off the relative quantities, representing in grains the
equivalent numbers to the amount of actinism which has influenced the
chemical compound.[119]

We have evidence which appears to prove that this chemical agent may
be absorbed by simple bodies, and that by this absorption an actual
change of condition, is produced, in many respects analogous to those
allotropic changes which we have previously considered. Chlorine, in
its ordinary state, does not combine with hydrogen in the dark. If we
employ the yellow medium of chlorine gas, for the purpose of analyzing
the sun’s rays previously to their falling upon some chemical compound
which is sensitive to actinic power, we shall find that the chlorine
obstructs all this actinism, and, however unstable the compound,
it remains unchanged. But the chlorine gas which has interrupted
this wonderful agent, appears to have absorbed it, and it is so far
altered in its constitution that _it will unite with hydrogen in the
dark_.[120] In like manner, if, of two portions of the same solution
of sulphate of iron, one is kept in the dark and the other exposed
to the sunshine, it will be found that the solution which has been
exposed will precipitate gold and silver from their combinations much
more speedily than that which has been preserved in darkness--the
temperature and every other condition being the same.

The phenomena of the Daguerreotype involve many strange conditions.
A plate of silver, on which a slight chemical action has been
established by the use of iodine, is exposed to the lenticular image
in the camera obscura. If allowed to remain under the influence of
these radiations for a sufficient length of time, a faithful picture
of the illuminated objects is delineated on the plate, as shown by
the visible decomposition and darkening of the iodized surface. The
plate is not, however, in practice allowed to assume this condition;
after an exposure of a few seconds the radiant influence is cut off,
and the eye cannot detect any evidence of change upon the yellow
plate. It is now exposed to the vapour of mercury, and that metal in
a state of exceedingly fine division is condensed upon the plate;
but the condensation is not uniformly spread upon its face. The
deposit of mercurial vapour is in exact proportion to the amount of
chemical action produced. Is the change, by which this peculiar power
of condensation is effected, a chemical, calorific, electrical, or
merely a molecular one? The evidences, at present, are not sufficient
to determine the question. It has lately been suggested, that the
mercury acts chemically only, and effects the full decomposition of
the iodide of silver; and that the picture is due to this, and not to
the deposition actually of the mercury vapour. In all probability we
have the involved action of several forces. We have some experiments
which show, clearly enough, that mercury is deposited in proportions
which correspond with the intensity of solar action. A chemically
prepared surface is not necessary to exhibit this result. A polished
plate of metal, of glass, of marble, or a piece of painted wood, being
partially exposed, will, when breathed upon, or presented to the action
of mercurial vapour, show that a disturbance has been produced upon
the portions which were illuminated, whereas no change can be detected
upon the parts which were kept in the dark. It was thought, until
lately, that a few chemical compounds, such as the iodide of silver,
the material employed in the Daguerreotype and Calotype,--chloride of
silver, the ordinary photographic agent,--a few salts of gold, and one
or two of lead and iron, were the only materials upon which these very
remarkable changes were produced. We now know that it is impossible
to expose any body, simple or compound, to the sun’s rays, without
its being influenced by this chemical and molecular disturbing power.
To take our examples from inorganic nature, the granite rock which
presents its uplifted head in firmness to the driving storm, the stones
which genius has framed into forms of architectural beauty, or the
metal which is intended to commemorate the great acts of man, and which
in the human form proclaims the hero’s deeds and the artist’s talent,
are all alike destructively acted upon during the hours of sunshine,
and, but for provisions of nature no less wonderful, would soon perish
under the delicate touch of the most subtile of the agencies of the
universe.

Niepce was the first to show that all bodies which underwent this
change during daylight possessed the power of restoring themselves
to their original conditions during the hours of night, when this
excitement was no longer influencing them. Resins, the Daguerreotype
plate, the unprepared metal tablet, and numerous photographic
preparations, prove this in a remarkable manner.[121]

The picture which we receive to-day, unless we adopt some method of
securing its permanency, fades away before the morrow, and we try to
restore it in vain. With some of our chemical preparations this is
very remarkably shown, but by none in so striking a manner as by paper
prepared with the iodide of platinum, which, being impressed with an
image by heliographic power, which is represented by dark brown tints,
restores itself in the dark, in a few minutes, to its former state of
a yellow colour, and recovers its sensibility to sunshine.[122] The
inference we alone can draw from all the evidences which the study
of actino-chemistry affords, is, that the hours of darkness are as
necessary to the inorganic creation as we know night and sleep to be
to the organic kingdom. But we must not forget that there does exist
in the solar rays a balance of forces which materially modifies the
amount of disturbing influence exerted by them on matter. Not only do
we find that the chemical action is not extended over the whole length
of the prismatic spectrum, but we discover that over spaces, which
correspond with the maximum points of light and heat, a protective
action is exerted. That is, that highly sensitive photographic agents,
which blacken rapidly under exposure to diffused daylight, are entirely
protected from change in full sunshine, if at the same time as a strong
light is thrown upon them by reflection, the yellow and extra red rays
are brought to bear upon their surface. Not only so, but by employing
media which will cut off all the chemical rays of the spectrum,
admitting freely at the same time the luminous and calorific rays, we
find that a protected band, the length of the spectrum, remains white,
whilst every other portion has blackened.[123]

Among the many curious instances of natural magic, none are more
remarkable than an experiment not long since proposed, by which
Daguerreotype pictures may be taken in absolute darkness to the human
eye. This is effected in the following manner:--A large prismatic
spectrum is thrown upon a lens fitted into one side of a dark chamber;
and as we know that the actinic power resides in great activity beyond
the violet ray, where there is no light, the only rays which we allow
to pass the lens into the chamber are those which are extra-spectral
and non-luminous. These are directed upon, any white object, and from
that object radiated upon a highly sensitive plate in a camera obscura.
Thus a copy of the subject will be obtained by the agency of radiations
which produce no sensible effect upon the optic nerve. This experiment
is the converse of those which show us that we may illuminate any
object with the strongest sunlight which has passed through yellow
glass, the yellow solution of sulphuret of calcium, or of the
bichromate of potash--these being non-transparent to the chemical
rays--and yet fail to secure any Daguerreotype copy of it, even upon
the most exquisitely sensitive plate. Indeed, the image of the sun
itself, when setting through an atmosphere which reduces its light to
a red or rich yellow colour, not only produces no chemical change,
but protects an iodized plate from it; and whilst every other part
of the tablet gives a picture of surrounding objects in the ordinary
character, the bright sun itself is represented by a spot upon which
no change has taken place.[124] In tropical climes, where a brilliant
sun is giving the utmost degree of illumination to all surrounding
objects, all photographic preparations are acted upon relatively more
slowly than in the climate of England, where the light is less intense.
As a remarkable instance of this fact, a circumstance may be mentioned,
which is curiously illustrative of the power of light to interfere with
actinism:--

A gentleman, well acquainted with the Daguerreotype process, obtained
in the city of Mexico all the necessary apparatus and chemicals,
expecting, under the bright light and cloudless skies of that climate,
to produce pictures of superior excellence. Failure upon failure was
the result; and although every care was used, and every precaution
adopted, it was not until the rainy season set in that he could secure
a good Daguerreotype of any of the buildings of that southern city.

The first attempts, which were made at the instigation of M. Arago,
by order of the French Government, to copy the Egyptian tombs and
temples, and the remains of the Aztecs in Central America, were
failures. Although the photographers employed succeeded to admiration
in Paris, in producing pictures in a few minutes, they found often that
an exposure of an hour was insufficient under the bright and glowing
illumination of a southern sky.

Experiments with the spectrum have been made in different latitudes,
and it is found, that, as we proceed towards the equator, a band which
is always left unchanged, corresponding exactly with the rays of
greatest illuminating power, regularly enlarges in size, thus proving
the increase of light over actinism--and the interfering power of the
former.

By increasing the sensibility of the photographic preparation, this
difficulty is overcome, and particularly when any organic compound
enters into the preparation. So that we are now enabled to copy nature
in all her varying moods, whether we employ our photographic tablets in
temperate Europe, or in tropical Africa.

The degree of sensibility which has been attained is remarkable. Mr.
Fox Talbot, by uniting a process devised by Dr. Woods, of Parsonstown,
and another which was first introduced by the author of this volume,
and combining them with an ether, obtains a most unstable compound,
which he thus employs. A glass plate is covered with albumen united
with the above solution, and then with nitrate of silver: this forms
the sensitive surface. The plate being placed in the dark, in a camera,
it is so adjusted that the image of a printed bill fixed upon a wheel
may fall upon it when uncovered, and the wheel illuminated. The wheel
is made to revolve with the utmost rapidity, in a perfectly dark
room, and the sensitive plate uncovered. Then the whirling bill is
illuminated for an inappreciably short space of time by the discharge
of a Leyden jar. Notwithstanding the rapid rate at which the pointed
paper is moving, and the instantaneous nature of the illumination--a
miniature flash of lightning--the bill is found to be copied with
unfailing fidelity upon the photographic plate. It unfortunately
happens, that the preparation by which this extraordinary degree of
sensibility is obtained, is very uncertain in its action--and hence it
is not generally useful; but here we have the evidence to show that
at a speed as rapid as that of a rifle-ball an impression may be made
upon a photographic plate. There are, however, some new processes which
promise eventually to rival the above for sensibility, and to be by no
means of difficult manipulation. Of this character is the collodion
process. The gun cotton dissolved in ether possesses some very great
accelerating properties, and in combination with the silver salts, and
one of the vegetable acids, it forms a sensitive surface upon which
pictures may be obtained in less than a second of time.

Colour, natural colour too, has been very decidedly secured. The sun
has been solicited to display his palette, and the answer has been a
picture in which colour for colour in all their fidelity have been
impressed. The plate upon which this result has been obtained is of a
dark brown colour, and the chromatic variety is, as it were, eaten out
by the solar rays. These colours have not yet been permanently fixed
upon the plate employed, but from the temporary degree of fixedness
which has been obtained, we may fairly hope that in a short time colour
may be rendered as permanent on the productions of the photographer
as on those of the painter. It is a curious and striking fact, that
in the preparation of these plates, salts are used which give colours
to flame; and according to the colour which is produced by them when
burning, so, on the photographic plate, is that colour impressed
with greater intensity than the others. To what is this leading us?
Mysteries surround our advances on the domain of truth. We dare not
speculate upon them: the time of their full development will arrive.

By the aid of this beautiful art, we are enabled to preserve the
lineaments of those who have benefited their race by their intellect,
or their heroism. We can hand down to future ages portraits of our own
Wellington, and the illustrious Arago, unerring in their truthfulness.
How great would be the joy of all, could we now obtain a daguerreotype
portrait of a Greek poet, or of a Roman philosopher, of a Sophocles,
or of a Seneca! How much discussion would be prevented did we possess
a calotype portrait of the Bard of Avon, or of the Philosopher of
Grantham!

By the agency of those very rays which give life and brilliancy to the
laughing eye and the roseate cheek, we can at once correctly trace the
outline of the features we admire, with all those shadowy details which
give a reality to the “presentment.” The objects of our love may be for
ever present with us in these self-painted pictures. The vicious, whom
we would avoid, may be made known to us by this unerring painter. The
process which nature employs is perfect; the imperfections are those of
man, and these being few, he may soon learn to remedy.

To the traveller, how valuable are the processes of photography! He
secures representations of those remains of temples which were in their
glory when Moses wrote. He copies by one operation a tomb at Karnac,
covered with myriads of hieroglyphics, or an inscribed stone in Arabia,
which it would occupy him days to trace. These he can carry to his home
and read at his leisure. The relics of hoar antiquity speaking to the
present of the past, and recording the histories of races which have
fleeted away like shadows, are thus preserved to tell their wondrous
tales.

The admirer of nature may copy her arrangements with the utmost
fidelity. Every modulation of the landscape, each projecting rock or
beetling tor--the sinuous river in its rapid flow--the meandering
stream, “gliding like happiness away;” and the spreading plains
over which are scattered the homes of honest industry and domestic
peace, intermingled with the towers of those humble temples in which
simple-hearted piety delights to “bow the head and bend their knee;”
these, all of these, may, by the sunbeam which illuminates the whole,
be faithfully pencilled upon our chemical preparations.

Our art enables us to do more even than this; we have but to present
our sensitive tablet to the moon, and she, by her own light, prints her
mountains and her valleys, and indicates with all truth the physical
conditions of her surface.

Any reference to the _chemical agency_ of LIGHT--_the luminous rays_ as
distinguished from the _chemical and calorific rays_--has been avoided
until we came to the consideration of this particular question of
chemical change.

Upon organic compounds, as, for instance, upon the colouring matter
of leaves and flowers, _light_ does exert a chemical power: and it
is found that vegetable colours are bleached, not by rays of their
own colour, but by those which are _complementary_ to them. A red dye
fades under the influence of a green ray, and a yellow under that of a
violet one, much more speedily than when exposed to rays of any other
colour; and this, it must be remembered, is due to the  ray
itself, and not to any _actinic_ power masked, as it were, behind the
colour, as is generally believed.[125] It was long a question whether
the decomposition of carbonic acid by plants was due to the luminous or
the chemical rays. It is now clearly established that the luminous rays
are the most active in producing this effect; which they do indirectly,
by exciting the vital powers of the organized structures. Therefore we
would refer this phenomenon of gaseous decomposition to a vital power
quickened by luminous excitement.[126]

We have already noticed some chemical phenomena due to heat,
particularly those experiments of Count Rumford’s, which appeared to
him to prove that the chemical agency of the sun’s rays was due to its
calorific power. Certain chemical phenomena, we know, may be produced
by thermic action; but the only variety of thermo-chemical action which
connects itself immediately with the solar radiations, belongs to a
class of rays to which the name of _Parathermic_ has been given, and to
which the scorching, as it is called, of plants, the browning of the
autumnal leaves, and the ripening of fruits, appear to be due.[127]
When we come to the consideration of those physical phenomena which
belong to the growth of plants, all these peculiarities of solar action
must be attended to in detail.

The manner in which we find the actinic power influencing electrical
action, also shows us that the equilibrium of forces is continued
through all the great principles of nature. If a galvanic arrangement
is made, by which small quantities of metals may be slowly precipitated
at one of the poles in the dark, and a similar arrangement be exposed
to sunshine, it will be found that no metal is deposited: the sun’s
rays have interfered with the decomposing power of the electrical
current. At the same time we learn, that by throwing a beam of light
upon a plate of copper which forms one of a galvanic pair, whilst
it is under the influence of an acidulated solution, an additional
excitation takes place, and the galvanometer will indicate the passage
of an increased current of electricity. These two dissimilar actions
appear enigmatical; but they may, there is no doubt, receive some
solution from the influence of different rays on the contrary poles
of the battery. One thing is quite evident,--electricity suffers a
disturbance of one order, by light; and an excitement of another by its
associated principles in the sunbeam. If a yellow glass is interposed
between the galvanic arrangement and the sun, the electro-chemical
precipitation goes on in the same manner as it would in perfect
darkness, and no extra excitement is produced upon the plates of the
battery. From this it would appear that actinism and not light is to be
regarded as the disturbing power.[128] It has already been shown that
yellow media possess the power of stopping back the chemical agent.

We have already, detailed many of the peculiarities of the different
varieties of Phosphori, which would seem to be the result of light.
Phosphorescence is probably excited by those rays which produce
no direct effect upon the eye. If we spread sulphuret of calcium
upon paper, and expose it to the action of the solar spectrum, it
is found to glow (in the dark) only over those spaces occupied by
the violet rays and the ordinarily dark rays beyond them; proving
that the excitation necessary to the development of the phenomena
of phosphorescence is due to a class of rays distinct from the true
light-giving principle, and more nearly allied to that principle or
power which sets up chemical decomposition. Whether the fluorescent
rays, before mentioned, which are found so abundantly over the space
which produces the greatest phosphorescent effect, are active in
producing the phenomena, is as yet an unsolved problem.

Vision and colour, calorific action, chemical change, molecular
disturbance, electrical phenomena, and phosphorescent excitation, all,
each one with a strange duality, are connected with the sunbeam.

We find, when we receive solar spectra upon iodized plates, or on
several kinds of photographic paper, that a line, over which no action
takes place, is preserved at the top and bottom of the impressed image,
and in many cases along the sides also. The only way in which this can
be accounted for, as the spectrum represents the sun in a distorted
form, is by supposing that rays come from the edges of the sun of a
different character from those which proceed from the centre of that
orb.[129]

Light from the centre of the solar disc is under different conditions
from that which comes from the edge of the sun: this is due to the
varying angle, which is presented to us by a circular body: calorific
action seems to be more strongly manifested when the envelope of
light, extending like an atmosphere to the sun, is thrown into great
agitation, and waves, and great hollows--solar spots--are produced.
There is some indication of the existence of a third condition on the
sun’s surface, to which probably belongs the mighty chemical power
which we call actinism. Electricity may be, as some have speculated,
the exciting agent; a constant and violent Aurora Borealis may exist on
the sun, and under the excitation of this force the others named may be
quickened into full activity.

That actinism is one of the great powers of creation we have abundant
proof. Nearly all the phenomena of chemical change which have been
referred to light, are now proved to be dependent upon actinic power;
and beyond the influence which has been ascertained to be exerted by
it upon all inorganic bodies, we shall have occasion to show still
further the dependence of the vegetable and animal worlds upon its
agency. The influence of the solar beams on vegetation is proved by
common experience; the closer examination of its action on vegetable
life is reserved for the chapter devoted to its phenomena. Of its
influence on animals nothing is very correctly known; but some early
experiments prove that they, like other organised bodies, are subject
to all the radiant forces, as indeed, independent of experiment, every
observation must teach. Certain it is, that organisation can take place
only where the sun’s rays can penetrate: where there is unchanging
darkness, there we find all the silence of death. Prometheus stole
fire from heaven, and gave the sacred gift to man, as the most useful
to him of all things in his necessities: by the aid of it he could
temper the severities of climate, render his food more digestible and
agreeable, and illuminate the hours of darkness. So says the beautiful
fiction of the Grecian mind,--which appears as the poetic dream or
prophetic glance of a gifted race, who felt the mysterious truth
they were yet unable to describe. Pheaton and Apollo are only other
foreshadowings of the creative energies which dwell in the glorious
centre of our universe. The poetry of the Hellenic people ascended
above the littlenesses of merely human action, and sought to interpret
the great truths of creation. Reflective, they could not but see that
some mysterious powers were at work around them; imaginative, they gave
to fine idealisations the government of those inexplicable phenomena.
Modern science has shown what vastly important offices the solar rays
execute, and that the principles discovered in a sunbeam are indeed the
exciters of organic life, and the disposers of inorganic form.

It must not be forgotten that we have already alluded to a speculation
which supposes this actinic influence to be diffused through all
nature, to be indeed the element to which chemical force in all its
forms is to be referred, and that it is merely excited by the solar
rays. This hypothesis receives some support from the very peculiar
manner in which chemical action once set up is carried on, independent
of all extraneous excitement, after the first disturbance has been
produced. If any of the salts of gold are exposed in connection with
organic matter, as on paper, to sunshine for a moment, an action is
begun, which goes on unceasingly in the dark, until the gold is reduced
to its most simple state.[130] The same thing occurs with chromate of
silver, some of the salts of mercury, argentine preparations combined
with protosulphate of iron or gallic acid, and some other chemical
combinations. These progressive influences point to some law not yet
discovered, which seems to link this radiant actinism with the chemical
agent existing in all matter.

This problem also connects itself with another class of facts which,
although due, in all probability, to a great extent, to calorific
radiations, and hence known under the general term of Thermography,
appear to involve both chemical and electrical excitation. From the
investigations of Moser and of others, we learn the very extraordinary
fact, that even inanimate masses act and react upon each other by
the influence of some dark radiations, and seem to exchange some of
the peculiarities which they possess. This appears generally in the
curious experiments which have been referred to, as confined merely
to form or structure. Thus an engraved plate will give to a polished
surface of metal or glass placed near it, after a very little time,
a neat distinct image of itself; that is, produce such a structural
disturbance as will occasion the plate to receive vapour differently
over those spaces opposite to the parts in cameo or in intaglio, from
what it does over the opposite. If a piece of wood is used instead of a
metal, there will, by similar treatment, be produced a true picture of
the wood, even to the representation of its fibres.[131]

It is also probable that chemical decomposition is produced by the
mere juxtaposition of different bodies. Iodide of gold or silver,
perfectly pure, has been placed upon a plate of glass, and a plate of
copper covered with mercury suspended over it: a gradual decomposition
of those salts is said to have been observed, iodide of mercury to
be formed, and the gold or silver salts reduced to a finely divided
metallic state.[132]

A body whose powers of radiating heat are low, being brought near
another whose radiating powers are more extensive, will, in the course
of a short time, undergo such an amount of molecular disturbance as
will effect a complete change in the arrangement of its surface, and
an impression of the body having the highest radiating powers will be
made upon the other. This impression is dormant, but may be developed
under the influence of vapour, or of oxidation.[133] A body, such
as charcoal, of low conducting power, being placed near another,
such as copper, which is a good conductor, will, in a very short
time, produce, in like manner, an impression of itself upon the metal
plate. Thus any two bodies, whose conducting or radiating powers are
dissimilar, being brought near each other, will occasion a molecular
disturbance, or impress the one with the image of the other. However
small the difference may be, an effect is perceived, and that of the
most extraordinary kind, giving rise to the production of actual images
upon each surface exposed. It is thus that a print on paper may be
copied on metal, by merely suspending it near a well-polished plate of
silver or copper for a few days. The white and black lines radiate very
differently; consequently an effect is produced on the bright metal in
the parts corresponding to the black lines, dissimilar to that which
takes place opposite to the white portions of the paper; and, on the
application of vapour, a true image of the one is found impressed upon
the other.[134]

Bodies which are in different electrical states act upon each other in
an analogous manner. Thus arsenic, which is highly electro-negative,
will, when placed near a piece of electro-positive copper, readily
impart to its surface an impression of itself, and so in like manner
will other bodies if in unlike conditions. Every substance physically
different (it signifies not whether as it regards colour, chemical
composition, mechanical structure, calorific condition, or electrical
state,) has a power of radiation by which a sensible change can be
produced in a body differently constituted.

Fable has told us that the magicians of the East possessed mirrors in
which they could at will produce images of the absent. Science now
shows us that representations quite sufficient to deceive the credulous
can be produced on the surface of polished metals without difficulty.
A highly polished plate of steel may be impressed with images of any
kind, which would remain invisible, the polished surface not being in
the least degree affected, as it regards its reflecting powers; but
by breathing over it, the dormant images would develope themselves,
and fade away again as the condensed moisture evaporated from the
surface.[135]

These, which are but a few selected from a series of results of an
equally striking character, serve to convince us that nature is
unceasingly at work, that every atom is possessed of properties by
which it influences every other atom in the universe, and that a most
important class of natural phenomena appear to connect themselves
directly with the radiant forces.

The alchemists observed that a change took place in chloride of silver
exposed to sunshine. Wedgwood first took advantage of that discovery to
copy pictures. Niepce pursued a physical investigation of the curious
change, and found that all bodies were influenced by this principle
radiated from the sun. Daguerre produced effects from the solar pencil
which no artist could approach to; and Talbot and others extended the
application. Herschel took up the inquiry; and he, with his usual
power of inductive search and of philosophical deduction, presented
the world with a class of discoveries which showed how vast a field of
investigation was opening for the younger races of mankind,--a field
in which a true spirit may reap the highest reward in the discovery of
new facts, and to which we must look for a further development of those
great powers with which we have already some slight acquaintance, and
for the discovery of higher influences which are not yet dreamed of in
our philosophy.

    If music, with its mysteries of sound,
      Gives to the human heart a heavenward feeling;
    The beauty and the grandeur which are found
    Spread like a vesture this fair earth around,
      Creation’s wond’rous harmonies revealing,
      And to the soul in truth’s strong tongue appealing,
    With all the magic of those secret powers,
      Which, mingling with the lovely band of light,
    The sun in constant undulation showers
    To mould the crystals, and to shape the flowers,
      Or give to matter the immortal might
    Of an embracing soul--should, from this sod,
    Exalt our aspirations all to God.


FOOTNOTES:

[117] See _Researches on Light_, by the Author.--Reference to any of
the works of the alchemists will prove the prevalence of the idea
expressed in the text. We find that gold was considered to be always
under the influence of light and solar heat.--“It is said of gold that
it waxeth cold towards daylight, insomuch that they who wear rings of
it may perceive when the day is ready to dawn.”--_Speculum Mundi, or a
Glass representing the face of the World_. Cambridge, 1643.

[118] Daguerre’s Report to the Academy of Sciences: _La Daguerréotype
Historique, et description des procédés du Daguerréotype et du Diorama_
(Paris, 1839); particularly the description of _Heliography_, by M.
Niepce. See also the letters by Niepce, published for the first time in
_Researches on Light_.

[119] “If a solution of peroxalate of iron be kept in a dark place,
or if it be exposed to 212° of Fahr. for several hours, it does not
undergo any sensible change in its physical properties, nor does it
exhibit any phenomenon which may be considered as the result of any
elementary action.

“If, however, it be exposed to the influence of solar light in a glass
vessel provided with a tube, the concentrated solution of oxalate
of iron soon presents a very interesting phenomenon: in a short
time the solution receiving the solar rays, developes an infinite
number of bubbles of gas, which rise in the liquor with increasing
rapidity, and give the solution the appearance of a syrup undergoing
strong fermentation. This ebullition always becomes stronger, and
almost tumultuous, when an unpolished glass tube is immersed in it
with a small piece of wood; the liquid itself is afterwards thrown
into ascending and descending currents, becomes gradually yellowish,
turbid, and eventually precipitates protoxalate of iron, in the form
of small brilliant crystals of a lemon-yellow colour, gas continuing
to evolve.” _Chemical action of light, and formation of Humboldtine
by it_; Phil. Mag., 1832, second series.--“When a solution of
platinum in nitro-muriatic acid, in which the excess of acid has been
neutralized by the addition of lime, and which has been well cleared
by filtration, is mixed with lime-water in the dark, no precipitation
to any considerable extent takes place for a long while,--indeed, none
whatever, though after very long standing a slight flocky sediment
is formed, after which the action is arrested entirely. But if the
mixture, either freshly made or when cleared by subsidence of this
sediment, is exposed to sunshine, it instantly becomes milky, and a
copious formation of a white precipitate (or a pale yellow one, if the
platinic solution be in excess) takes place, which subsides quickly
and is easily collected. The same takes place more slowly in cloudy
daylight.”--_On the action of light in determining the precipitation of
Muriate of Platinum by Lime water_; being an extract from a letter from
Sir John F. W. Herschel, K.H., F.R.S., &c., to Dr. Daubeny.--Phil. Mag.
1832.

[120] _On a change produced by Exposure to the Beams of the Sun, in
the properties of an elementary substance_, by Professor Draper;
_On the changes which bodies undergo in the dark_, by Robert Hunt:
Report of the Thirteenth Meeting of the British Association, vol.
xii,--_Description of the Tithonometer, an instrument for measuring
the chemical force of the Indigo-tithonic rays_: by J. W. Draper,
M.D.--Philosophical Magazine, Dec. 1843, vol. xxiii.

[121] For several illustrations of this remarkable phenomenon, see _On
the Action of the Rays of the Solar Spectrum on Vegetable Colours,
and on some new Photographic Processes_; by Sir John F. W. Herschel,
Bart., K.H., F.R.S.--Phil. Trans. June, 1842, vol. cxxxiii.; _On
certain improvements on Photographic Processes described in a former
communication, and on the Parathermic Rays of the Solar Spectrum_;
by Sir John F. W. Herschel, Bart., K.H., F.R.S., &c., in a letter
addressed to S. Hunter Christie.--Phil. Trans. 1843, vol. cxxxiv.

[122] Sir J. F. W. Herschel; see also _Researches on Light_, by the
Author.

[123] Attention has been directed to the protecting action of certain
rays of the spectrum by Sir John Herschel and others. See the
Eighteenth Report of the British Association for an experiment by
the Author, in which it was proved that all the LIGHT rays protected
photographic papers from chemical change, and, therefore, convincingly
show that light and actinism were not similar powers.

[124] “Having noticed, one densely foggy day, that the disc of the sun
was of a deep red colour, I directed my apparatus towards it. After
ten seconds of exposure, I put the prepared plate in the mercury box,
and I obtained a round image perfectly black;--the sun had produced no
photogenic effect. In another experiment, I left the plate operating
for twenty minutes; the sun had passed over a certain space of the
plate, and there resulted an image seven or eight times the sun’s
diameter in length; it was black throughout, so that it was evident,
wherever the red disc of the sun had passed, not only was there a
want of photogenic action, but the red rays had destroyed the effect
produced previous to the sun’s passage. I repeated these experiments
during several days successively, operating with a sun of different
tints of red and yellow. These different tints produced nearly the same
effect; wherever the sun had passed, there existed a black band.”--Mr.
Claudet, _On different properties of Solar Radiation, modified by
 glass media, &c._: Phil. Trans. 1847. Part 2.

[125] “It may also be observed that the rays effective in destroying
a given tint are, in a great many cases, those whose union produces a
colour complementary to the tint destroyed, or at least one belonging
to that class of colours to which such complementary tint may be
referred. For example, yellows tending towards orange are destroyed
with more energy by the blue rays; blue by the red, orange, and yellow
rays; purples and pinks by yellow and green rays.”--Sir J. F. W.
Herschel, _On the action of the rays of the Solar Spectrum on Vegetable
Colours_: Phil. Trans., vol. cxxxiii. 1842.

[126] The following memoirs and works are necessary to a complete
history of the inquiry:--_Experiments and observations relating
to various branches of natural philosophy, with a continuation of
the observation on air_: by Dr. Priestley. London, 1779. _Mémoires
Physico-chimiques, &c._: by J. Senebier. _Expériences sur les
végétaux_, by De la Ville: Paris, 1782; and Phil. Trans. 1782.
_Observations sur les expériences de M. Ingenhousz_: by De la Ville;
Roz. obs. 23, 290. _Expériences propres à développer les effets de la
lumière sur certaines plantes_: by Tessier; Mém. de l’Ac. des Sc. de
Paris, 1783, p. 132; Licht. Mag. iv. 4, 146. _Sur la vertu de l’eau
impregnée d’air fixe pour en obtenir, par le moyen des plantes et de
la lumière du soleil, de l’air déphlogistiqué_: by Ingenhousz; Roz.
obs. 24, 337. _Expériences sur l’action de la lumière solaire dans la
végétation_: by Senebier; Genève et Paris, 1788, p. 61. _Extrait des
expériences de M. Senebier sur l’action de la lumière solaire dans la
végétation_: by Hasenfratz; Ann. Chim. iii. 2nd. ser. 266. _Expériences
relatives à l’influence de la lumière sur quelques végétaux_: by De
Candolle; Jour. de Ph. lii. 124: Voigt’s Mag. ii. 483; Gilb. Ann.
xiii. 372; Mém. des Sav. Etr. i. 329. _Recherches chimiques sur la
végétation_: by Saussure; Ann. Chim. l. 225; Jour. de Ph. lvii. p.
393; Gilb. Ann. xviii 208. _Recherches sur la respiration des plantes
exposées à la lumière du soleil_; by Ruhland; Ann. Ch. Ph. iii. 411;
Jour. de Ph. 1816. _On the action of light upon plants, and of plants
upon the atmosphere_: by Dr. Daubeny; Phil. Trans. cxxvii January,
1836. _On the action of yellow light in producing the green colour, and
of indigo light on the movements of plants_: by P. Gardner; Phil. Mag.
xxiv.; Bibl. Univ. xlix. p. 376, and lii. p. 381. _On the influence of
light on plants_: by R. Hunt; Phil. Mag. xxiv. p. 96; Bibl. Univ. xlix.
p. 383; Athen. 1844. _Note on the decomposition of carbonic acid by
the leaves of plants, under the influence of yellow light_: by Draper;
Phil. Mag. xxv. p. 169. _On the action of the yellow rays of light on
vegetation_: by Harkness; Phil. Mag. xxv. p. 339. _Influence des rayons
solaires sur la végétation_: by Zantedeschi; Inst. No. 541, p. 157.

[127] Sir John Herschel’s Memoirs already referred to; and _Reports on
the influence of the Solar Rays on the growth of Plants_, by Robert
Hunt: Report of the British Association for the Advancement of Science,
for 1847.

[128] _Memoir on the Constitution of the Solar Spectrum_, presented at
the meeting of the Academy of Sciences, 1842, by M. Edmond Becquerel;
_Des effets produits sur les corps par les rayons solaires_, par M.
Edmond Becquerel, aide au Muséum d’Histoire Naturelle: Mémoire présenté
à l’Académie des Sciences, le 23 Octobre, 1843.--“Dans le courant de
ce mémoire, j’ai employé les noms de rayons lumineux, chimiques, et
phosphorogéniques, pour désigner, dans chaque cas, la portion des
rayons solaires qui agit pour produire, en particulier, les effets
lumineux, chimiques, et phosphorogéniques; mais cela est sans préjudice
de l’opinion que je viens d’émettre touchant l’existence d’un seul et
même rayonnement.”

“My reply is this,” says M. Arago, in his paper entitled
_Considerations relative to the action of Light_: “It is by no means
proved that the photogenic modifications of sensitive substances
result from the action of the solar light itself. The modifications
are, perhaps, engendered by invisible radiations mixed with light
properly so called, proceeding with it, and being similarly refracted.
In this case, the experiment would prove not only that the spectrum
formed by these invisible rays is not continuous, that there are
solutions of continuity as in the visible spectrum, but also that in
the two superposed spectra these solutions correspond exactly. This
would be one of the most curious, one of the most strange results of
physics.”--Taylor’s Scientific Memoirs.

[129] The chemical evidence of this will be found in Sir John
Herschel’s Memoir _On the Solar Spectrum_, and particularly as
exemplified in the changes produced on the tartrate of silver. Similar
influences are described as observed on a Daguerreotype plate, in
a paper entitled _Experiments and Observations on Light which has
permeated  media, and on the Chemical Action of the Solar
Spectrum_; by Robert Hunt.--Philosophical Magazine, vol. xxvi. 1840.

[130] This peculiar continuance of an effect has frequently been
observed in many of the photographic processes. In a note to a memoir
_On certain improvements in Photographic processes_, Sir John Herschel
thus refers to this property:--“The excitement is produced on such
paper by the ordinary moisture of the atmosphere, and goes on slowly
working its effect in the dark, apparently without other limit than is
afforded by the supply of ingredients present. In the case of silver it
ultimately produces a perfect _silvering_ of all the sunned portions.
Very singular and beautiful photographs, having much resemblance to
Daguerreotype pictures, are thus produced; the negative character
changing by keeping, and by quite insensible gradations to positive,
and the shades exhibiting a most singular _chatoyant_ change of colour
from ruddy-brown to black, when held more or less obliquely. No doubt,
also, gold pictures with the metallic lustre might be obtained by the
same process, though I have not tried the experiment.”

[131] The details of this curious subject may be studied in the
following memoir and communications:--_On vision and the action of
light on all bodies_: by Professor Ludwig Moser, of Königsberg; from
Poggendorff’s Annalen, vol. lvi. p. 177, No. 6, 1845. _Some remarks
on Invisible Light_: by Professor Ludwig Moser, of Königsberg; from
Poggendorff’s Annalen, vol. lvi. p. 569, No. 8. _On the power which
light possesses of becoming latent_: by Professor Ludwig Moser, of
Königsberg; from Poggendorff’s Annalen, vol. lvii. No. 9, p. 1. 1842.
_On certain spectral appearances, and on the discovery of latent
light_: by J. W. Draper, M.D., Professor of Chemistry in the University
of New York; Phil. Mag. p. 348, Nov. 1842. _On a new imponderable
substance, and on a class of chemical rays analogous to the rays of
dark heat_: by Professor Draper; Phil. Mag., Dec. 1842. _On the action
of the rays of the solar spectrum on the Daguerreotype plate_; by Sir
J. F. W. Herschel, Bart.; Phil. Mag., Feb. 1843. See remarks in this
paper on the use which Moser has made of  glasses: also a
communication by Professor Draper, _On the rapid Detithonizing power of
certain gases and vapours, and on an instantaneous means of producing
spectral appearances_: Phil. Mag., March 1843; and _On the causes which
concur in the production of the images of Moser_: Comptes Rendus, Nov.
1842. See _Scientific Memoirs_, vol. iii.

[132] This fact was first observed by myself, and described in the
paper already referred to, Philosophical Magazine, vol. xxii. p. 270.
It does not, however, appear to have attracted the attention of any
other observer.

[133] _On Thermography, or the Art of copying Engravings or any printed
characters from paper or plates of metal, and on the recent discovery
of Moser, relative to the formation of images in the dark_, by Robert
Hunt: Reports of the Royal Cornwall Polytechnic Society for 1842, and
Philosophical Magazine, vol. xxi. p. 462.--_On the Spectral Images of
M. Moser_, by Robert Hunt: Philosophical Magazine, vol. xxiii. p. 415.

[134] _Catalytic force, or attraction of surface concerned in the
diffusive power of gases: an occult energy or power in saturated saline
solutions_; Prater.--Mechanic’s Magazine, vol. xlv. p. 106. _Ueber
elektrische Abbildungen_; by G. Karsten.--Poggendorff’s Annalen, vol.
lvii. p. 402.--Melloni and Brewster may be consulted for much that is
most remarkable connected with radiation from  surfaces.

[135] Cornelius Agrippa is said to have possessed such a mirror.
The Chinese make mirrors which, when placed in a particular light,
show upon their polished faces the pattern on the back of the metal,
although it is invisible in every other position. This is effected by
giving different degrees of hardness to the various parts of the metal.
In _Natural Magic_, by Sir David Brewster, several curious experiments
belonging to this class are named.




CHAPTER IX.

ELECTRICITY.

  Discovery of Electrical Force--Diffused through all Matter--What
    is Electricity?--Theories--Frictional Electricity--Conducting
    Power of Bodies--Hypothesis of two Fluids--Electrical
    Images--Galvanic Electricity--Effects on Animals--Chemistry of
    Galvanic Battery--Electricity of a Drop of Water--Electro-chemical
    Action--Electrical Currents--Thermo-Electricity--Animal
    Electricity--Gymnotus--Torpedo--Atmospheric Electricity--Lightning
    Conductors--Earth’s Magnetism due to Electrical Currents--Influence
    on Vitality--Animal and Vegetable Development--Terrestrial
    Currents--Electricity of Mineral Veins--Electrotype--Influence of
    Heat, Light, and Actinism on Electrical Phenomena.


If a piece of amber, _electrum_, is briskly rubbed, it acquires the
property of attracting light bodies. This curious power excited the
attention of Thales of Miletus; and from the investigations of this
Grecian philosopher we must date our knowledge of one of the most
important of the natural forces--Electricity.

If an inquiring mind had not been led to ask why does this curious
natural production attract a feather, the present age, in all
probability, would not have been in possession of the means by which it
is enabled to transmit intelligence with a rapidity which equals the
poet’s dream of the “swift-winged messengers of thought.” To this age
of application a striking lesson does this amber teach. Modern utility
would have regarded Thales as a madman. Holding a piece of yellow
resin in his hand, rubbing it, and then picking up bits of down, or
catching floating feathers, the old Greek would have appeared a very
imbecile, and the _cui bono_ generation would have laughed at his silly
labours. But when he announced to his school that this amber held a
soul or essence, which was awakened by friction, and went forth from
the body in which it previously lay dormant, and brought back the small
particles floating around it, he gave to the world the first hint of
a great truth which has advanced our knowledge of physical phenomena
in a marvellous manner, and ministered to the refinements and to the
necessities of civilisation. Each phenomenon which presents itself to
us, however simple it may appear to be, is an outward expression of
some internal truth, the interpretation of which is only to be arrived
at by assiduous study, but which, once discovered, directs the way to
new knowledge, and gives to man a great increase of power. There is no
truth so abstract that it will not find its useful application, and
every example of the ministration of Physical Science to the purposes
of humanity is an evidence of the value of abstract study, and a reply
to the utilitarian in his own language.

Electricity appears to be diffused through all nature; and it is,
beyond all doubt, one of the most important of the physical forces, in
the great phenomena of creation. In the thunder-cloud, swelling with
destruction, it resides, ready to launch its darts and shake the earth
with its explosions: in the aërial undulations, silent and unseen, it
passes, giving the necessary excitement to the organisms around which
it floats. The rain-drop--the earth-girdling ocean--and the ringing
waters of the hill-born river, hold locked this mighty force. The
solid rocks--the tenacious clays which rest upon them--the superficial
soils--and the incoherent sands, give us evidence of the presence of
this agency; and in the organic world, whether animal or vegetable, the
excitement of electrical force is always to be detected.

In the solar radiations we have perhaps the prime mover of this
power. In our atmosphere, when calm and cloudless, a great ocean of
light, or when sombre with the mighty aspect of the dire tornado, we
can constantly detect the struggle between the elements of matter to
maintain an equilibrium of electrical force.

Diffused throughout matter, electricity is ever active; but it must
be remembered that although it is evidently a necessary agent in all
the operations of nature, that it is not the agent to which everything
unknown is to be referred. Doubtless the influence of this force is
more extensive than we have yet discovered; but that is an indolent
philosophy which refers, without examination, every mysterious
phenomenon to the influence of electricity.

The question, what is electricity? has ever perplexed, and still
continues to agitate, the world of science. While one set of
experimentalists have endeavoured to explain the phenomena they have
witnessed, upon the theory that electricity is a peculiar subtile
fluid pervading matter, and possessing singular powers of attraction
and repulsion, another party find themselves compelled to regard
the phenomena as giving evidence of the action of two fluids which
are always in opposite states; while again, electricity has been
considered by others as, like the attraction of gravitation, a mere
property of matter.[136] Certain it is, that in the manifestations
of electrical phenomena we have, as it appears, the evidence of two
conditions of force; but of the states of _positive_ or _negative_, of
_vitreous_ or _resinous_ electricity, we have a familiar explanation
in the assumption of some current flowing into or out of the material
body,--of some principle which is ever active in maintaining its
equilibrium, which, consequently, must act in two directions, and
always exhibit that duality which is a striking characteristic of this
subtile agent. It is a curious, and it should be an instructive fact,
that each of the three theories of electricity is capable of proof,
and has, indeed, been most ably supported by the rigorous analysis
of mathematics. When we remember that some of the most enlightened
investigators of this and the past age have severally maintained,
in the most able manner, these dissimilar views, we should hesitate
before we pronounce an opinion upon the cause or causes of the very
complicated phenomena of electrical force.

Although we discover, in all the processes of nature, the
manifestations of this principle or force in its characteristic
conditions, it will be necessary, before we regard the great phenomena,
to examine the known sources from which we can most readily evoke the
mighty power of electricity. If we rub a piece of glass or resin, we
readily render this agent active; these substances appear, by this
excitement, to become surrounded by an attractive or a repellent
atmosphere. Let us rub a strip of writing paper with Indian rubber,
or a strip of Gutta Percha with the fingers, in the dark, and we have
the manifestation of several curious phenomena. We have a peculiar
attracting power; we have a luminous discharge in the shape of a spark;
and we have very sensible evidence of muscular disturbance produced by
applying the knuckle to the surface of the material. In each case we
have the development of the same power.

Every substance in nature is an electric, and, if so disposed that its
electricity may not fly off as it is developed, we may, by friction,
manifest its presence, and, indeed, measure its quantity or its force.
All bodies are not, however, equally good electrics; shell-lac, amber,
resins, sulphur, and glass, exhibiting more powerfully the phenomena
of frictional or mechanical electricity, than the metals, charcoal,
or plumbago. Solid bodies allow this peculiar principle to pass along
them also in very different degrees. Thus electricity travels readily
through copper and most other metals, platinum being the worst metallic
conductor. It also passes through living animals and vegetables, smoke,
vapour, rarified air, and moist earth; but it is obstructed by resins
and glass, paper when dry, oils, and dry metallic oxides, and in a very
powerful manner by Gutta Percha.[137]

If, therefore, we place an electric upon any of those non-conducting
bodies, the air around being well dried, we are enabled to gather
a large quantity of the force for the production of any particular
effect. Taking advantage of this fact, arrangements are made for the
accumulation and liberation at pleasure of any amount of electricity.

A Leyden phial,--so called from its inventor, Musschenbroek, having
resided at Leyden,--is merely a glass bottle lined within and without,
to within a few inches of the top, with a metal coating. If a wire or
chain, carrying an electric current, is allowed to dip to the bottom
of the bottle, the inner coat of the jar becomes charged, or gathers
an excess, whilst the outer one is in its natural condition--one is
said to be in a _positive_, and the other in a _negative_ state. If
the two coatings are now connected by a good conductor, as a piece of
copper wire, passing from one to the other, the outside to the inside,
a discharge, arising from the establishment of the equilibrium of the
two coatings, takes place; and, if the connection is made through the
medium of our bodies, we are sensible of a severe disturbance of the
nervous system.

The cause of the conducting and non-conducting powers of bodies we know
not; they bear some relation to their conducting powers for caloric;
but they are not in exact obedience to the same laws. When we consider
that resin, a comparatively soft body, in which, consequently,
cohesive attraction is not very strong, is an imperfect conductor,
and that copper, in which cohesion is much more powerful, is a good
conductor, we may be disposed to consider that it is regulated by the
closer approximation of the particles of matter. But in platinum the
corpuscular arrangement must be much more dense than it is in copper,
and yet it is, compared with it, a very bad conductor.[138]

We have now learnt that we may, by friction, excite the electricity
in a vitreous substance; but it must not be forgotten that we cannot
increase the quantity which is, under ordinary conditions, natural to
the electric; to do so, we must in some way establish a channel of
communication with the earth, from which, through the medium we excite,
we draw our supply. We have the means of confining this mighty force
within certain limits of quantity and of time. If we place bodies which
are susceptible of electrical excitation in a sensible degree upon
insulating ones, we may retain for a considerable time the evidences of
the excitement, in the same way as with the Leyden jar; but there is a
constant effort to maintain a balance of conditions, and the body in
which we have accumulated any extraordinary quantity by conduction soon
returns to its natural state.

A very simple means may be adopted of showing what is thought to be
one of the many evidences in favour of two electricities. If the
wire carrying the current flowing from the machine, is passed over
paper covered with nitrate of silver, it produces no change upon it;
but if the wire which conveys the current to the instrument, when
it is excited, is passed over the same paper, the silver salt is
decomposed.[139] We may, however, explain this result in a satisfactory
manner, upon the hypothesis that the decomposition is produced by the
abstraction of electricity, rather than by any physical difference in
the fluid itself. By frictional electricity we may produce curious
molecular disturbances, and give rise to molecular re-arrangements,
which have been called “electrical images,” in glass, in stone, and in
the apparently less tractable metals: these images are rendered visible
by the manner in which, according to their electrical states, some
lines receive any particular powder, or vapour, which is repelled from
other spaces. Many of the great natural phenomena, such as Lightning
and Thunder, the Aurora Borealis, and Meteors, may be imitated in a
curiously exact manner by the electrical machine and a few familiar
arrangements.[140]

Voltaic electricity, as the active force produced by chemical change
is commonly called, in honour of the illustrious Volta, is now to
be considered. It differs from frictional electricity in this:--the
electricity developed by friction of the glass plate or cylinder of
the electrical machine is a discharge with a sort of explosion. It
is electricity suddenly liberated from the highest state of tension,
whereas that which is generated by chemical action in the voltaic
battery is a steady flowing current. We may compare one to the ignition
of a mass of gunpowder at once, and the other to the slow burning of
the same quantity spread out into a very prolonged train.

There are numerous ways in which we may excite the phenomena of
Voltaism, but in all of them the decomposition of one of the elements
employed appears to be necessary. This is the case in the arrangements
of batteries in which two dissimilar metals, zinc and copper, silver
and platinum, or the like, is immersed in fluids; the zinc or the
silver are gradually converted into soluble salts, which are dissolved,
whilst the copper or platinum is protected from any action. The most
simple manner of illustrating the development of this electricity is by
placing a piece of silver on the tongue, and a piece of zinc or lead
underneath it. No effect will be observed so long as the two metals
are kept asunder, but when their edges are brought together, a slight
tremulous sensation will pass through the tongue, a saline taste be
distinguished by the palate, and if in the dark, light will be observed
by the eye.

This, the germ of the most remarkable of the sciences, was noticed by
Sulzar, fifty years before Galvani observed the convulsions in the
limbs of frogs, when excited by the action of dissimilar metals; but
the former paid little attention to the phenomenon, and the discovery
led to no results.

When Galvani’s observant mind was directed to the remarkable fact that
the mere contact of two dissimilar metals with the moist surface of
living muscles produced convulsions, there was an awakening in the soul
of that philosopher to a great fundamental truth, which was nurtured
by him, tried and tested, and preserved to work its marvels for future
ages.

Although the world of science looks back to Volta as the man who gave
the first true interpretation of this discovery, yet the ordinary world
will never disconnect this important branch of physical science from
the name of Galvani, and chemical electricity in all its forms will for
ever be known under the familiar name of Galvanism. And it must not be
forgotten, that the phenomena of the manifestation of electricity, in
connection with the conditions of vitality, are entirely due to Galvani.

Let us examine the phenomena of Galvanism in its most simple phases:--

If we place a live flounder upon a plate of zinc, put a shilling on its
back, and then touch both metals with the ends of a metallic wire, the
fish will exhibit painful convulsions. The zinc becomes oxidized by
the separation of oxygen from the fluid on the surface with which it is
in contact, whilst hydrogen gas is liberated at that surface touched
by the other metal. Here we have, in the first place, a chemical
change effected, then a peculiar muscular disturbance. Each successive
combination or decomposition, like a pulsation, is transmitted along
the circuit from one extremity to the other. How the impulse which is
derived from the zinc is transmitted through the body of the animal, or
the tongue, to the silver or copper is the next consideration.

We can only understand this upon the supposition that a series of
impulses are communicated in the most rapid manner along the connecting
line; the idea of a current, although the term is commonly employed,
tends to convey an imperfect impression to the mind. It would seem
rather that a disturbance throughout the entire circuit is at once set
up by a series of vibrations or impulses communicated from particle to
particle, and along the strange net-work of nerves. One set of chemical
elements have a tendency to develope themselves at that point where
vibration is first communicated to the mass from a better conductor
than it is, and another set at the point where it passes from the
body to a better conductor than itself. The cause of this is to be
sought for in the laws which regulate molecular constitution--by which
chemical affinity is disturbed,--and a new attractive force exerted,
in obedience to which the vital energy is itself agitated. We must
not, however, forget that it is probable after all, although not yet
susceptible of proof, that the electricity does nothing more than
disturb or quicken the unknown principles upon which chemical and vital
phenomena depend; being, indeed, a secondary agent.[141]

Notwithstanding our long acquaintance with the phenomena of galvanism,
there are but few who entertain a correct idea of the enormous amount
of electricity which is necessary to the existing conditions of matter.
To Faraday we are indebted for the first clear set of deductions from a
series of inductive researches, which are of the most complete order.
He has proved, by a series of exceedingly conclusive experiments, that
if the electrical power which holds a grain of water in combination,
or which causes a grain of oxygen and hydrogen to unite in the right
proportions to form water, could be collected and thrown into the
condition of a voltaic current, it would be exactly the quantity
required to produce the decomposition of that grain of water, or the
liberation of its elements, hydrogen and oxygen.[142]

By direct experiment it has been proved that one equivalent of zinc in
a voltaic arrangement evolves such a quantity of electricity in the
form of a current, as, passing through water, will decompose exactly
one equivalent of that fluid. The law has been thus expressed:--The
electricity which decomposes, and that which is evolved by the
decomposition of a certain quantity of matter, are alike. The
equivalent weights of bodies are those quantities of them which contain
equal quantities of electricity; electricity determining the equivalent
number, because it determines the combining force.[143]

The same elegant and correct experimentalist has shown that zinc and
platinum wires, one-eighteenth of an inch in diameter, and about half
an inch long, dipped into water in which is mixed sulphuric acid so
weak that it is not sensibly sour to the tongue, will evolve more
electricity in one-twentieth of a minute than is given by thirty turns
of a large and powerful plate electrical machine in full action, a
quantity which, if passed through the head of a cat, is sufficient to
kill it as by a flash of lightning. Pursuing this interesting inquiry
yet further, it is found that a single grain of water contains as
much electricity as could be accumulated in 800,000 Leyden jars, each
requiring thirty turns of the large machine of the Royal Institution to
charge it,--a quantity equal to that which is developed from a charged
thunder-cloud. “Yet we have it under perfect command,--can evolve,
direct, and employ it at pleasure; and when it has performed its full
work of electrolisation, it has only separated the elements of a single
grain of water.”

It has been argued by many that the realities of science will not admit
of anything like a poetic view without degrading its high office; that
poetry, being the imaginative side of nature, has nothing in common
with the facts of experimental research, or with the philosophy which
generalises the discoveries of severe induction. If our science was
perfect, and laid bare to our senses all the secrets of the inner
world; if our philosophy was infallible, and always connected one
fact with another through a long series up to the undoubted cause of
all--then poetry, in the sense we now use the term, would have little
business with the truth; it would, indeed, be lost or embodied, like
the stars of heaven, in the brightness of a meridian sun. But to take
our present fact as an example, how important a foundation does it
offer upon which to build a series of thoughts, capable of lifting
the human mind above the materialities by which it is surrounded,--of
exalting each common nature by the refinement of its fresh ideas to a
point higher in the scale of intelligence,--of quickening every impulse
of the soul,--and of giving to mankind the most holy longings.

What does science tell us of the drop of water? Two gases, the one
exciting life and quickening combustion, the other a highly inflammable
air, are, by the influence of a combination of powers, brought into
a liquid globe. We can, from this crystal sphere, evoke heat, light,
electricity, and actinism in enormous quantities; and beyond these
we can see powers or forces, for which, in the poverty of our ideas
and our words, we have not names; and we learn that each one of these
principles is engaged in maintaining the conditions of the drop of
water which refreshes organic nature, and gives gladness to man’s
dwelling-place.

Has poetry a nobler theme than this? Agencies are seen like winged
spirits of infinite power, each one working in its own peculiar way,
and all to a common end,--to produce, under the guidance of omnipotent
rule, the waters of the rivers and the seas. As the great ocean mirrors
the bright heaven which overspreads it, and reflects back the sunlight
and the sheen of the midnight stars in grandeur and loveliness; so
every drop of water, viewed with the knowledge which science has given
to us, sends back to the mind reflections of yet distant truths which,
rightly followed, will lead us upwards and onwards in the tract of
higher intelligences,--

    “To the abodes where the eternals are.”

In the discoveries connected with electricity, we have results of
a more tangible character than are as yet connected with the other
physical forces; and it does appear that this science has advanced
our knowledge of nature and of the mysteries of creation far more
extensively than any other department of purely experimental inquiry.

The phenomena of electro-chemical action are so strange that we must
return for a moment to the consideration of the decomposition of
water, and the appearance of hydrogen at one pole, and of oxygen at
the other. It appears that some confusion of our ideas has arisen
from the views which have been received of the atomic constitution of
bodies. We have been accustomed to regard water,--to take that body as
an example of all,--as a compound of two gases, hydrogen and oxygen;
an equivalent, or one atom of the first, united to an equivalent or
one atom of the last, forming one atom of water. This atom of water we
regard as infinitely small; consequently a drop of water is made up of
many hundreds of these combined atoms, and a pint of water of not less
than 10,000 drops. Now, if this pint of water is connected with the
wires of a galvanic battery, although their extremities may be some
inches apart, for every atom of oxygen liberated at one pole, an atom
of hydrogen is set free at the other. It has been thought that an atom
has undergone decomposition at one point, its oxygen being torn from
it, and then there has arisen the difficulty of sending the atom of
hydrogen through all the combined atoms of water across to the other
pole. A series of decompositions and recompositions have been supposed
to take place, and the communication of effects from particle to
particle.

An attracting power for one class of bodies has been found in one pole,
which is repellent to another class; and the reverse order has been
detected at the opposite pole of a galvanic arrangement.[144] That
is, the wire which carries the current from an excited zinc plate has
a relation to all bodies, which is directly opposite to that which
is exhibited by the wire conveying the current from, or completing
the circuit with, the copper plate. The one, for instance, collects
and carries acids and the like, the other the metallic bases. At the
extremity of one galvanic wire, placed into a drop of water, oxygen is
always liberated; and at the end of the other, necessary to complete
the circuit with the battery, hydrogen is set free.

It appears necessary, to a clear understanding of what takes place in
this experiment, that we should regard each mass, howsoever large, as
the representative of a single atom. Nor is this difficult, as the
following illustration will show.

Let us take one particle of common salt (_chloride_ of _sodium_)
weighing less than a grain, and put it into a hundred thousand grains
of distilled water. In a few minutes the salt has diffused itself
through the whole of the fluid, and in every drop we can detect
chlorine and soda. We cannot believe that this grain of salt has split
itself up into a hundred thousand parts; we conceive rather that the
phenomenon of solution is one of diffusion. One infinitely elastic body
has interpenetrated with another.

Instead of an experiment with a pint of water, let us take our stand
on Dover heights, and, with a gigantic battery at our command, place
one wire into the ocean on our own shores, and convey the other through
the air across the channel, and let its extremity dip into the sea
off Calais pier--the experiment is a practicable one--we have now an
electrical circuit of which the British channel forms a part, and the
result will be exactly the same as that which we may observe in a
watch-glass with a drop of water.

We cannot suppose that the instantaneous and simultaneous effect
which takes place in the water at Calais and at Dover, is due to
anything like what we have studied under the name of convection, when
considering Heat.

A thousand balls are placed in a line touching each other; the first
ball receives a blow, and the last ball flies off with a force exactly
equal to the power applied to the first; none of the intermediate balls
being moved.

We cannot conceive that the particle _A_ excites the particle _B_ next
it, and so on through the series between the two shores; but regarding
the channel as one large drop, charged with the electric principle as
we know it to be, it is excited by undulation or tremor throughout
its width, and we have an equivalent of oxygen thrown off on one side
of the line, and an exact equivalent of hydrogen at the other, the
electro-chemical influence being exerted only where the current or
motion is transferred from one medium to another.[145] The imperfect
character of this view is freely admitted; no other, consistent with
known facts, presents itself by which the effect can be explained. The
fact stands as a truth; the hypothesis by which it is attempted to
be interpreted is open to doubt, and it is opposed to some favourite
theories.

Before we pass to the consideration of the other sources of
electricity, it is important we should understand that no chemical
or physical change, however slight it may be, can occur without the
development of electrical power. If we dissolve a salt in water, if
we mix two fluids together, if we condense a gas, or convert a fluid
into vapour, electricity is disturbed, and may be made manifest to our
senses.[146]

It has been shown that this power may be excited by friction
(machine electricity) and by chemical action (voltaic electricity,
galvanism); it now remains to speak of the electricity developed by
heat (thermo-electricity), the electricity exhibited under nervous
excitement by the gymnotus and torpedo (animal electricity); magnetism
and its phenomena being reserved for a separate consideration.

If a bar of metal is warmed at one end and kept cool at the other,
an electrical current circulates through the bar, and may be carried
off by connection with any good conductor, and shown to exhibit the
properties of ordinary electricity. The metals best suited for showing
the effects of thermo-electricity appear to be bismuth and antimony. By
binding two bars of these metals together at one end, and connecting
the other ends with a galvanometer, it will be discovered that an
electric current passes off through the instrument by the slightest
variation of temperature. Merely clasping the two metals, where bound
together, with the finger and thumb, is sufficient to exhibit the
phenomenon. By a series of such arrangements,--which form what have
been called thermo-electric multipliers,--we obtain the most delicate
measurers of heat with which philosophers are acquainted, by the aid of
which Melloni has been enabled to pursue his beautiful researches on
radiant caloric.

That this electricity is identical with the other forms has been proved
by employing the current thus excited for the purpose of producing
chemical decomposition, magnetism, and electric light.[147]

The phenomenon of thermo-electricity--the discovery of Seebeck, is
another proof of the very close connection of the physical forces. We
witness their being resolved as it were into each other, electricity
producing heat, and heat again electricity; and it is from these
curious results that the arguments in favour of their intimate
relations and actual identity have been drawn. It will, however, be
found to be the best philosophy to regard these forces as dissimilar,
until we are enabled to prove them to be only modified forms of one
principle or power. At the same time it must not be forgotten that
in natural operations we invariably find the combined action of
several forces producing a single phenomenon. The important fact to be
particularly regarded is, that we have evidence that every substance
which is unequally heated becomes the source of this very remarkable
form of electricity.[148]

There exist a few fishes gifted with the very extraordinary power of
producing electrical phenomena by an effort of muscular or nervous
energy.

The _Gymnotus electricus_, or electrical eel, and the _Raia torpedo_,
a species of ray, are the most remarkable. This power is, it would
appear, given to these curious creatures for purposes of defence, and
also for enabling them to secure their prey. The _Gymnotus_ of the
South America rivers, will, it is said, when in full vigour, send forth
a discharge of electricity sufficiently powerful to knock down a man,
or to stun a horse; while it can destroy fishes, through a considerable
space, by exerting its strange artillery.[149]

Faraday’s description of a _Gymnotus_, paralyzing and seizing its
prey, is too graphic and important to be omitted.

“The _Gymnotus_ can stun and kill fish which are in very various
positions to its own body; but on one day, when I saw it eat, its
action seemed to me to be peculiar. A live fish, about five inches in
length, caught not half a minute before, was dropped into the tub.
The _Gymnotus_ instantly turned round in such a manner as to form a
coil, inclosing the fish, the latter representing a diameter across
it; a shock passed, and there, in an instant, was the fish struck
motionless, as if by lightning, in the midst of the waters, its side
floating to the light. The _Gymnotus_ made a turn or two to look for
its prey, which, having found, he bolted, and then went about searching
for more. A second smaller fish was given him, which being hurt in the
conveyance, showed but little signs of life, and this he swallowed at
once, apparently without shocking it. The coiling of the _Gymnotus_
round its prey had, in this case, every appearance of being intentional
on its part, to increase the force of the shock, and the action is
evidently well suited for that purpose, being in full accordance
with the well-known laws of the discharge of currents in masses of
conducting matter; and though the fish may not always put this artifice
in practice, it is very probable he is aware of its advantages, and may
resort to it in cases of need.”[150]

Animal electricity has been proved to be of the same character as that
derived from other sources. The shock and the spark are like those
of the machine; and the current from the animal, circulating around
soft iron, like galvanic electricity, has the property of rendering it
magnetic.

It is important that we should now review these conditions of
electrical force in connexion with the great physical phenomena of
nature.

It is sufficiently evident, from the results which have been examined,
that all matter, whatever may be its form or condition, is for ever
under the operation of the physical forces, in a state of disturbance.
From the centre to the surface all is in an active condition: a state
of mutation prevails with every created thing; and science clearly
shows that influences are constantly in action which prevent the
possibility of absolute repose.

Under the excitement of the several agencies of the solar beams, motion
is given to all bodies by the circulation of heat, and a full flow of
electricity is sent around the earth to perform its wondrous works.
The solar influences, which regulate, and possibly determine, every
physical force with which we are acquainted, are active in effecting
an actual change of state in matter. The sunbeam of the morning falls
on the solid earth, and its influence is felt to the very centre.
The mountain-top catches the first ray of light, and its base, still
wrapt in mists and darkness, is disturbed by the irradiating power.
The crystalline gems, hidden in the darkness of the solid rock, are
dependent, for that form which makes them valued by the proud and gay,
on the influence of those radiations which they are one day to refract
in beauty. The metals locked in the chasms of the rifted rocks are, for
all their physical peculiarities, as dependent on solar influence as is
the flower which lifts its head to the morning sun, or the bird which
sings “at heaven’s high gate.”

Let us, then, examine how far electricity, as distinguished from the
other powers, acts in producing any of these effects.

We find electricity in the atmosphere, which the electrical kite of Dr.
Franklin proved to be identical with that principle produced by the
friction of glass. In the grandeur and terror of a thunderstorm, many
see nothing but manifestations of Almighty wrath. When the volleys of
the bursting cloud are piercing the disturbed air, and the thunders
of the discharge are pealing their dreadful notes above our heads,
the chemical combinations of the noxious exhalations arising from the
putrefying animal and vegetable masses of this earth are effected,
elements fitted for the purposes of health and vegetation are formed,
and brought to the ground in the heavy rains which usually follow these
storms. Science has taught man this--has shown him that the “partial
evil” arising from the “winged bolt” is a “universal good;” and, more
than this, it has armed him with the means of protecting his life and
property from the influence of lightnings. So that, like Ajax, he can
defy the storm. By metallic rods, carried up a chimney, a tower, or a
mast, we may form a channel through which the whole of the electricity
of the most terrific thunder-cloud may be carried harmlessly into
the earth or the sea; and it is pleasing to observe that at length
prejudice has been overcome, and “conductors” are generally attached
to high buildings, and to most of the ships of our navy.[151] It was
discovered that the devastating hailstorms of the south of France
and Switzerland, so destructive to the vineyards and crops, were
accompanied by evidences of great electrical excitation, and it was
proposed to discharge the electricity from the air by means of pointed
metallic rods. These have been adopted, and, it is said, with real
advantage--each rod protecting an area of one hundred yards. Thus it
is that science ministers to our service; and how much more pleasing
is it to contemplate the lightning, with the philosopher, as an agent
destroying the elements of pestilence, and restoring the healthfulness
of the air we breathe, than with the romancer, to see in it only the
dreaded aspect of a demon of destruction.

The laws which regulate the spread of a pestilence are unknown. The
difficulties of the investigation are great, but they are by no means
insurmountable. A plague passes from the east to the west across
the world--it spreads mourning over the gayest cities, and sorrow
sitteth in the streets. The black death rises in the Orient: it goes
on in unchecked strength, and only finishes its course when it has
made the circuit of the civilized world. The cholera spreads its
ebon wings--mankind trembles--watches its progress, and looks upon
the path which is marked by the myriads of the dead, who have fallen
before the dire fiend. The diseases pass away--the dead are buried,
and all is forgotten. The rush and the riot of life are pursued: and
until man is threatened with another advent, he cares not to trouble
himself. Accompanying the last visitation, there appear certain
peculiar meteorological conditions, which point a line of inquiry. It
may or may not be the path which leads to the truth, but certainly
its indications are worthy of careful examination. It may be asked,
can weak man stop a pestilence; can a mortal’s puny hand <DW44> the
afflictions of the Almighty? The question asked--it must be answered in
reverence, yet without fear. No human power can produce a change in the
physical conditions of the earth, or of the air; and if our diseases
are connected with those changes, as beyond all doubt a number of them
are, they lie above man’s control. But when there are indications that
causes secondary to these are producing some dire effect, and when
we know that these secondary causes may be modified, it is sufficient
evidence to prove that man is permitted to control thus far the
afflictions which are sent to try his powers.

We find a disease winging its way from lane to alley and closed court,
sweeping with destructive violence its way through damp cellars and
crowded attics; it is rife with mischief along the banks of reeking
ditches, and on the borders of filthy streams. Certain it is,
therefore, that some ultimate connexion exists between the conditions
of dirt and this speedy death. Can science tell of these? has it yet
searched out the connecting link? Let the question be answered by a few
facts.

When the cholera first made its appearance, and subsequently, it has
been observed that the electrical intensity of the atmosphere was
unusually low.

The disease has departed, and it is then found that the electricity of
the air has been restored to its ordinary condition.

This appears to show some connexion; but how do these conditions link
this physical force with the ditch-seeking disease?

From all stagnant places, from all the sinks of overcrowded humanity,
from fermenting vegetable and from putrefying animal matter, there
are constantly arising poisonous exhalations to do their work of
destruction.

Where death and decay is a law, this must of necessity constantly
occur; but the poisonous reek may be diffused, or it may be
concentrated, and Nature has provided for this, and ordered the means
for rendering the poison harmless.

By the agency of electricity,--probably, too, by the influence of
light,--the oxygen in the air undergoes a peculiar change, by which
it is rendered far more energetic than it is in its ordinary state.
This is the condition to which the name of _ozone_ has been applied.
Now, this ozone, or this peculiar oxygen, always exists in the air we
breathe; but its quantity is subject to great and rapid variations. It
is found that when electrical intensity is high the quantity of this
principle is great; when the electrical intensity is low, as in the
cholera years, the proportion of ozone is relatively low.

This remarkable chemical agent possesses the power of instantly
combining with organic matter,--of removing with singular rapidity all
noxious odours; and it would appear to be the most active of all known
disinfectants.

May we not infer from the facts stated that the pestilence we dread is
the result of organic poison, which from a deficiency of ozone,--its
natural antidote,--exerts its baneful influences on humanity. This
deficiency is due to alterations in the electrical character of the
air, possibly dependent upon phenomena taking place in the sun itself,
or it may be still more directly influenced by variations in the
character of solar light, which we have not yet detected, by which the
conditions of the electric power are determined.

This may be a line along which it is fair to push enquiry. But such
an enquiry must be made in all the purity of the highest inductive
philosophy, and speculation must be held firmly in the controlling
chains of experiment and observation. In the truths, however, which are
known to us, there is so much harmony and consistence that even the
melancholy theme links itself--a tragedy--with the Poetry of Science.

It has been thought, and much satisfactory evidence has been brought
forward to support the idea, that the earth’s magnetism is due to
currents of electricity circulating around the globe; as a great
natural current from east to west--that, indeed, it has an unvarying
reference to the motion of the earth in relation to the sun.[152]

These terrestrial currents, as they have without doubt a very important
bearing on the structural conditions of the rock-formations and the
distribution of minerals, require an attentive consideration; but we
must, in the first place, examine, as far as we know, the influences
exerted, or supposed to be exerted, by electricity, in its varied forms.

The phenomena of vitality have, by many, been considered as immediately
dependent upon its influence; and a rather extensive series of
experiments has been made in support of this hypothesis. The researches
of Philip on the action of the organs of digestion, when separated
from their connection with the brain, but united with a galvanic
battery, have been proved by Dr. Reid to be delusive;[153] since, as
the organ is not removed from the influence of the living principle,
it is quite evident that the electricity here is only secondary to
some more important power. Matteucci has endeavoured to show that
nervous action is intimately connected with electric excitation, and
that electricity may be made a measurer of nervous irritability.[154]
There can be no doubt that a peculiar susceptibility to excitement
exists in some systems, and this is very strikingly shown in the
disturbances produced by electric action; but in the experiments which
have been brought forward we have only the evidence that a certain
number of muscular contractions are exhibited in one animal by a
current of electricity, giving a measured effect by the voltameter,
which are different from those produced upon another by a current of
the same power. An attempt has recently been made by Mr. A. Smee to
reduce the electrical phenomena connected with vitality to a more
exact system than had hitherto been done. We cannot, however, regard
the attempt as successful. The author has trusted almost entirely
to analogical reasoning, which is in science always dangerous.[155]
In the development of electricity during the operation of the vital
force, we see only the phenomena produced by the action of any two
dissimilar chemical compounds upon each other. It has been thought
that the structure of the brain presents an analogy to that of the
galvanic battery, and the nerves represent the conducting wires.
Although, however, some of the conditions appear similar, there are
many which have no representatives in either the mechanical structure
or the physical properties of the brain, so far as we know it. That
the brain is the centre, the source, and termination of sensation is
very clearly proved by physiological investigations. That the nerves
are the media by which all sensation is conveyed to the brain, and
also the instruments by which the will exerts its power over the
muscles, is equally well established. But to say that we have any
evidence to support the idea that electricity has aught to do directly
with these great physiological phenomena, would be a bold assertion,
betraying a want of due caution on the part of the investigator. That
electric effects are developed during the operations of vitality is
most certain. Such must be the case, from the chemical changes taking
place during respiration and digestion, and the mechanical movements
by which, even during external repose, the necessary functions of the
body are carried on. Whether electricity is the cause of these, or an
effect arising from them, we need not stop to examine, as this is,
in the present state of our knowledge, a mere speculation. We have
no evidence that electricity is an exciting power, but rather that
it is one of those forces which tend to establish the equilibrium of
matter. When disturbed--when its equilibrium is overset--it does, in
its efforts to regain its stability, produce most remarkable effects.
An electrical machine must be rubbed to exhibit any force. In all
galvanic arrangements, even the most simple, dissimilar bodies are
brought together, and the latent electricity of both is disturbed;
and, even in the magnet, it is only when this takes place that its
electrical powers are developed. In the _Gymnotus_, electricity appears
to be dependent upon the power of the will of the animal; but even in
this extraordinary fish, it is only under peculiar conditions that the
electrical excitement takes place, and “what they inflict, they feel”
during the restoration of that equilibrium which is necessary to their
healthy state. In every case, therefore, we see that some power far
superior to this is the ultimate cause; indeed, light and heat, and
probably actinism, appear to stand superior to this principle; and on
these, in some combined mode of action, in all probability, sensible
electricity is dependent. Beyond even these elements, largely as they
are engaged in the organic and inorganic changes of this world, there
are occult powers which may never be understood by finite beings.
We advance step by step from the most solid to the most ethereal of
material creations, and we examine a series of extraordinary effects
produced by powers which we know not whether to regard as material or
immaterial, so subtile are they. On these, it appears, we may exhaust
our inductive investigations--we may discover the laws by which these
principles act upon the grosser elements, and develope phenomena of
a very remarkable kind which have been unobserved or misunderstood.
Whether light, heat, and electricity are modifications of one power,
or different powers very closely united in action, is a problem we may
possibly solve; but to know what they are, appears to be beyond the
hopes of science; and it were idle to dream of elucidating the causes
hidden beyond these forces, and by which they are regulated in all
their actions on dead or living matter.

M. Du Bois Raymond, from a series of researches remarkable alike for
their difficulty and the delicacy with which they have been pursued,
draws the following, amongst many others, as his conclusions as to the
connection of electricity and vital phenomena.

The muscles and nerves, including the brain and the spinal chord, are
endowed during life with an electromotive power, which acts according
to a definite law.

The electromotive power _lasts after death_, or in dissected nerves and
muscles after separation from the body of the animal, as long as the
excitability of the nervous and muscular fibre; whether these fibres
are permitted to die gradually from the cessation of the conditions
necessary to the support of life, or whether they are suddenly deprived
of their vital properties by heat or chemical action.

Let us not suppose for a moment that these conclusions indicate in the
remotest degree that electricity is life,--that vital power is due to
electricity.

During life, with every motion, and, indeed, with every emotion,
whether we move a muscle or exert the mind, there is a change of state.
The result of this is chemical phenomena,--heat and electricity; but
these are not life. We excite them equally by giving motion to a dead
mass.

Notwithstanding the assertions of those who have zealously followed
the path of Mesmer, and examined, or they have thought so, the
psychological effects dependent upon some strange physiological
conditions, there is not an experiment on record,--there is not an
observation worthy of credit, which shows that electricity has any
connection with their results. All around their subject is uncertainty:
doubt involves every experiment, and deception clouds a large number.
Some few grains of truth, and these are sufficiently strange, are mixed
up in an enormous mass of error.

All the phenomena of life,--of the _vis vitæ_ or vitality, are beyond
human search. All the physical forces, or elements, we may examine by
the test of experiment: but the principle on which sensation depends,
the principle even upon which vegetable _life_ depends, cannot be
tested. Life is infinitely superior to every physical force; it holds
them all in control, but is not itself controlled by them; it keeps
its state sacred from human search,--the invisible hidden behind the
veil of mortality.

During changes in the electrical conditions of the earth and
atmosphere, vegetables give indications of being in a peculiar manner
influenced by this power. It is proved by experiments that the leaves
of plants are among the best conductors of electricity, and it has
hence been inferred that it must necessarily be advantageous to
vegetation. That vegetable growth is, equally with animal growth,
subject to electricity, as one of its quickening powers, must be
admitted; but all experiments which have been fairly tried with the
view of stimulating the growth of plants by its agency, have given
results of a negative character.[156] That a galvanic arrangement may
produce chemical changes in the soil, which may be advantageous to the
plant, is probable; but that a plant can be brought to maturity sooner,
or be made to develope itself more completely, under the direct action
of electrical excitation, appears to be one of those dreams of science
which will have a place amongst the marvels of alchemy and the fictions
of astrology. An attentive examination of all the conditions necessary
for the satisfactory development of the plant, will render it evident,
that although the ordinary electrical state of the earth and atmosphere
must influence the processes of germination and vegetable growth,
yet that any additional excitement must be destructive to them. The
wonders wrought by electrical power are marvellous; a magic influence
is exerted by it, and naturally the inquiring mind is led at first to
believe that electricity is the all-powerful principle of creation; but
a little reflection will serve to convince us that it is a subordinate
agent, although a powerful one.

In proceeding with our examination of the phenomena which present
themselves in connection with the terrestrial currents, we purposely
separate magnetism from those more distinct electro-chemical agencies
which play so important a part in the great cosmical operations.

Electricity, we have already stated, flows through or involves all
bodies; but, like heat, it appears to undergo a very remarkable change
in becoming associated with some forms of matter. We have the phenomena
of magnetism when an electric current circulates through a metallic
wire, and it would appear that all other bodies acquire a peculiar
polar condition under the influence of this principle, which will be
explained in the next chapter.

The rocks, taken as masses, will not conduct an electric current when
dry: granite, porphyry, slate, and limestone, obstructing its passage
even through the smallest spaces. But all the metallic formations admit
of its circulating with great freedom. This fact it must, however,
be remembered does not in any way interfere with the hypothesis of
the existence of electricity in all bodies, in what we must regard as
its latent state, from which, under prescribed conditions, it may be
readily liberated. Neither does it affect the question of circulation,
in relation to the great diffusion of electricity which we suppose to
exist through all nature, and to move in obedience to some fixed law.
We know that through the superficial strata electric currents circulate
freely, whether they are composed of clay, sand, or any mixture of
these with decomposed organic matter; indeed, that with any substance
in a moist state they suffer no interruption.

The electricity of mineral veins has attracted much attention, and
numerous investigations into the phenomena which these metalliferous
formations present, have been made from time to time.[157]

By inserting into the mass of a copper _lode_, or vein, in situ, a
metallic wire, which shall be connected with a measurer of galvanic
action, a wire also from the instrument being brought into contact with
another _lode_, an immediate effect is generally produced, showing
that a current is traversing through the wires from one _lode_ to the
other, and completing the circulation probably over the dark face of
the rock in which the fissures forming the mineral veins exist.[158]
The currents thus detected are often sufficiently active to deflect
a magnetic needle powerfully, to produce, slowly, electro-chemical
decomposition, and to render a bar of iron magnetic. These currents
must not be confounded with the great electrical movements around the
earth. They are only to be detected in those mineral formations in
which there is evidence of chemical action going on, and, the greater
the amount of this chemical operation, the more energetic are the
electrical currents.[159] We have, however, very good evidence that
these local currents have, of themselves, many peculiar influences. It
not unfrequently happens that owing to some great disturbance of the
crust of the earth, a mineral vein is dislocated, and one part either
sinks below, or is lifted above its original position; the fissures
formed between the two being usually filled in with clay or with
crystalline masses of more recent formation than the fissure itself. It
is frequently found that these “_cross courses_,” as they are called in
mining language, contain ores of a different character from those which
constitute the mineral vein; for instance, in them nickel, cobalt, and
silver are not unfrequently discovered. When these metals are so found,
they almost invariably occur between the ends of the dislocated lode,
and often take a curvilinear direction, as if they were deposited along
a line of electrical force.[160]

In the laboratory such an arrangement has been imitated, and in a
mass of clay fixed between the galvanic plates, after a short period
a distinct formation of a mineral vein has taken place.[161] By the
action, too, of weak electrical currents, Becquerel, Crosse, and
others, have been successful in imitating nature so far as to produce
crystals of quartz and other minerals. In addition to this evidence, in
support of the electrical theory of the origin of mineral veins, it
can be experimentally shown that a schistose structure may be given to
clays and sandstone by voltaic action.[162]

There is often a very remarkable regularity in the direction of mineral
veins: throughout Cornwall, for instance, they most commonly have a
bearing from the E. of N. to the W. of S. It has hence been inferred
that they observe some relation to the magnetic poles of the earth.
However this may be, it is certain that the ore in any lodes which
are in a direction at right angles, or nearly so, to this main line,
differs in character from that found in these, so called, east and west
lobes.[163]

The sources of chemical action in the earth are numerous. Water
percolating through the soil, and finding its way to great depths
through fissures in the rocks, carries with it oxygen and various
salts in solution. Water again rising from below, whether infiltrated
from the ocean or derived from other sources, is usually of a high
temperature, and it always contains a large quantity of saline
matter.[164] By these causes alone chemical action must be set
up. Chemical change cannot take place without a development of
electricity: and it has been proved that the quantity of electricity
required for the production of any change is equal to that contained
in the substances undergoing such change. Thus a constant activity is
maintained within the caverns of the rock by the agency of the chemical
and electrical elements, and mutations on a scale of great grandeur are
constantly taking place under some directive force.

The mysterious gnome, labouring--ever labouring--in the formation of
metals, and the mischievous Cobalus of the mine, are the poor creations
of superstition. A vague fear is spread amongst great masses of mankind
relative to the condition of the dark recesses of the earth; a certain
unacknowledged awe is experienced by many on entering a cavern, or
descending a mine: not the natural fear arising from the peculiarity of
the situation, but the result of a superstitious dread, the effect of a
depraved education, by which they have been taught to refer everything
a little beyond their immediate comprehension to supernatural causes.
The spirit of demon worship, as well as that of hero worship, has
passed from the early ages down to the present; and under its influence
the genii of the East and the demons of the West have preserved their
traditionary powers.

Fiction has employed itself with the utmost license in giving glowing
pictures of treasures hidden in the earth’s recesses. The caverns
of Chilminar, the cave of Aladdin, the abodes of the spirits of the
Hartz, and the dwellings of the fairies of England, are gem-bespangled
and gold-glistening vaults, to which man has never reached. The
pictures are pleasing; but although they have the elements of poetry
in them, and delight the young mind, they want the sterling character
of scientific truth; and the wonderful researches of the plodding
mineralogist have developed more beauty in the caverns of the dark rock
than ever fancy painted in her happiest moments.

In all probability the action of the sun’s rays upon the earth’s
surface, producing a constantly varying difference of temperature,
and also the temperature which has been observed as existing at great
depths, give rise to thermo-electrical currents, which may play an
important part in the results thus briefly described.

In connection with these great natural operations, explaining them,
and being also, to some extent, explained by them, we have the very
beautiful application of electricity to the deposition of metals,
called the Electrotype.

Applying the views we have adopted to this beautiful discovery,[165]
the whole process by which these metallic deposits are produced will
be yet more clearly understood. By the agency of the electric fluid,
liberated in the galvanic battery, a disturbance of the electricity of
the solution of copper, silver, or gold, is produced, and the metal is
deposited; but, instead of allowing the acid in combination to escape,
it has presented to it some of the same metal as that revived, and,
consequently, it combines with it, and this compound, being dissolved,
maintains the strength of the solution.[166] A system of revival, or
decomposition, is carried on at one pole, and one of abrasion, or more
correctly speaking, of composition and solution, at the other. By
taking advantage of this very extraordinary power of electricity, we
now form vessels for ornament or use, we gild or silver all kinds of
utensils, and give the imperishability of metal to the most delicate
productions of nature--her fruits, her flowers, and her insects;--and
over the finest labours of the loom we may throw coatings of gold or
silver to add to their elegance and durability. Nor need we employ the
somewhat complex arrangement of the battery: we may take the steel
magnet, and, by mechanically disturbing the electricity it contains, we
can produce a current through copper wires, which may be used, and is
extensively employed, for gilding and silvering.[167] The earth itself
may be made the battery, and, by connecting wires with its mineral
deposits, currents of electricity have been secured, and used for the
production of electrotype deposit.[168]

The electrotype is but one of the applications of electricity to the
uses of man. This agent has been employed as the carrier of thought;
and with infinite rapidity, messages of importance, communications
involving life, and intelligences outstripping the speed of coward
crime, have been communicated. There will be no difficulty in
understanding the principle of this, although many of the nice
mechanical arrangements, to ensure precision, are of a somewhat
elaborate character. The entire action depends on the deflection of a
compass-needle by the passage of an electric current along its length.
If at a given point we place a galvanic battery, and at twenty or one
hundred miles distance from it a compass-needle, between a wire brought
from, and another returning to the battery, the needle will remain true
to its polar direction so long as the wires are unexcited; but the
moment connection is made, and the circuit is complete, the electricity
of the whole extent of wire is disturbed, and the needle is thrown at
right angles to the direction of the current. Provided a connection
between two points can be secured, however remote they are from each
other, we thus, almost instantaneously, convey any intelligence. The
effects of an electric current would appear at a distance of 576,000
miles in a second of time; and to that distance, and with that speed,
it is possible, by Professor Wheatstone’s beautiful arrangements, to
convey whispers of love or messages of destruction.

The enchanted horse of the Arabian magician, the magic carpet of the
German sorcerer, were poor contrivances, compared with the copper
wires of the electrician, by which all the difficulties of time and
the barriers of space appear to be overcome. In the Scandinavian
mythology we find certain spiritual powers of evil enabled to pass
with imperceptible speed from one remote point to another, sowing the
seeds of a common ruin amongst mankind. Such is the morbid creation
of a wild yet highly endowed imagination. The spirit of evil diffuses
itself in a remarkable manner, and, indeed, we might almost assign to
it the power of ubiquity; but in reality its advance is progressive,
and time enters as an element into any calculation on its diffusion.
Electricity is instantaneous in action; as a spirit of peace and
good-will it can overtake the spirit of evil, and divert it from its
designs. May we not hope that the electrical telegraph, making, as it
must do, the whole of the civilized world enter into a communion of
thought, and, through thought, of feeling with each other, will bind us
up in one common brotherhood, and that, instead of misunderstanding and
of misinterpreting the desires and the designs of each other, we shall
learn to know that such things as “natural enemies” do not exist? To
hope to break down the great barrier of language is perhaps too much;
but assuredly we may hope that, as we must do when closer and more
intimate relations are secured by the aids of science, the barrier of
prejudice may be razed to the ground, and not one stone left to stand
upon another? Our contentions, our sanguinary wars, consecrated to
history by the baptism of blood, have in every, or in nearly every,
instance sprung from the force of prejudice, or the mistakes of
politicians, whose minds were narrowed to the limits of a convention
formed for perpetuating the reign of ignorance.

And can anything be more in accordance with the spirit of all that we
revere as holy, than the idea that the elements employed by the All
Infinite in the works of physical creation shall be made, even in the
hands of man, the ministering angels to the great moral redemption of
the world? Associate the distant nations of the earth, and they will
find some common ground on which they may unite. Mortality compels a
dependence; and there are charities which spring up alike in the breast
of the savage and the civilized man, which will not be controlled by
the cold usages of pride, but which, like all truths, though in a still
small voice, speak more forcibly to the heart than errors can, and
serve as links in the great chain which must bind mankind in a common
brotherhood. “None are all evil,” and the best have much to learn of
the amenities of life from him who yet lives in a “state of nature,” or
rather from him whose sensualities have prevailed over his intellectual
powers, but who still preserves many of the noblest instincts, to give
them no higher term, which other races, proud of their intelligence,
have thrown aside. Time and space have hitherto prevented the
accomplishment of this; electricity and mechanics promise to subdue
both; and we have every reason to hope those powers are destined to
accelerate the union of the vast human family.

Electrical power has also been employed for the purpose of measuring
time, and by its means a great number of clocks can be kept in a state
of uniform correctness, which no other arrangement can effect. A
battery being united with the chief clock, which is itself connected
by wires with any number of clocks arranged at a distance from each
other, has the current continually and regularly interrupted by the
beating of the pendulum, which interruption is experienced by all the
clocks included in the electric circuit; and, in accordance with this
breaking and making contact, the indicators or hands move over the dial
with a constantly uniform rate. Instead of a battery the earth itself
has supplied the stream of electric fluid, with which the rate of its
revolutions has been registered with the utmost fidelity.[169]

Electricity, which is now employed to register the march of time,
rushes far in advance of the sage who walks with measured tread,
watching the falling sands in the hour-glass.

The earth is spanned and the ocean pierced by the wires of the electric
telegraph. Already, from the banks of the Thames to the shores of the
Adriatic, our electric messenger will do our bidding. The telegraph
is making its way through Italy, and it is dipping its wires in the
Mediterranean, soon to reach the coast of Africa. They will then run
along the African shores to Egypt and Turkey, and still onward until
they unite with the telegraphs of India, of which three thousand miles
are in progress. From Hindostan these wondrous wires will run from
island to island in the Indian Archipelago, and thus connect Australia
and New Zealand with Europe.

In a few years we may expect to have an instantaneous report in London
of the extraordinary “nugget” discovered by some fortunate gold-digger;
and the exile from his native land in the Islands of the South Pacific
Ocean, may learn every hour, if he will, of the doings of his family
and friends in some village home of England.


FOOTNOTES:

[136] _Traité de Physique_: M. Biot, vol. vii. Becquerel: Annales
de Chimie, vol. xlvi.-xlix. Faraday’s _Experimental Researches in
Electricity_, 2 vols., 1830-1844. _A Speculation touching Electric
Conduction and the Nature of Matter_: by Michael Faraday, D.C.L.,
F.R.S.; Philosophical Magazine, vol. xxiv., 1836. _Objections to the
theories severally of Franklin, Dufay, and Ampère, with an attempt to
explain Electrical Phenomena by statical or undulatory polarization_:
by Robert Hare, M.D., Emeritus Professor of Chemistry in the University
of Pennsylvania.

[137] “A good piece of gutta percha will insulate as well as an equal
piece of shell-lac, whether it be in the form of sheet, or rod, or
filament; but being tough and flexible when cold, as well as soft
when hot, it will serve better than shell-lac in many cases where the
brittleness of the latter is an inconvenience. Thus it makes very good
handles for carriers of electricity in experiments on induction; not
being liable to fracture in the form of thin band or string, it makes
an excellent insulating suspender; a piece of it in sheet makes a
most convenient insulating basis for anything placed on it. It forms
excellent insulating plugs for the stems of gold-leaf electrometers,
when they pass through sheltering tubes, and larger plugs form good
insulating feet for electrical arrangements; cylinders of it, half an
inch or more in diameter, have great stiffness, and form excellent
insulating pillars. In these and in other ways its power as an
insulator may be useful.”--_On the use of Gutta Percha in Electrical
Insulation_: by Dr. Faraday; Philosoph. Mag., March, 1848.

The following deductions have been given by Faraday, in his _Researches
in Electricity_, a work of most extraordinary merit, being one of the
most perfect examples of fine inductive philosophy which we possess in
the English language:--

“All bodies conduct electricity in the same manner from metals to lacs
and gases, but in very different degrees.

“Conducting power is in some bodies powerfully increased by heat, and
in others diminished, yet without one perceiving any accompanying
essential electrical difference, either in the bodies, or in the change
occasioned by the electricity conducted.

“A numerous class of bodies insulating electricity of low intensity,
when solid, conduct it very freely when fluid, and are then decomposed
by it.

“But there are many fluid bodies which do not sensibly conduct
electricity of this low intensity; there are some which conduct it and
are not decomposed; nor is fluidity essential to decomposition.

“There are but two bodies (sulphuret of silver and fluoride of lead)
which, insulating a voltaic current when solid, and conducting it when
fluid, are not decomposed in the latter case.

“There is no strict electrical distinction of conduction which can as
yet be drawn between bodies supposed to be elementary, and those known
to be compounds.”

[138] Faraday’s _Speculation on the Nature of Matter_, already referred
to.

[139] _Experimental Researches_: by Dr. Faraday. _Chemical
Decomposition_, p. 151.

[140] Karsten; Poggendorff’s _Annalen_, vol. lvii.

[141] _Traité Expérimental de l’Électricité et du Magnétisme_:
Becquerel, 1834, Priestley’s _Introduction to Electricity_. _On
Electricity in Equilibrium_: Dr. Young’s Lectures.

[142] Faraday’s _Experimental Researches on Electricity_. This
philosopher has shown, by the most conclusive experiments, “that
the electricity which decomposes, and that which is evolved by the
decomposition of, a certain quantity of matter, are alike. What an
enormous quantity of electricity, therefore, is required for the
decomposition of a single grain of water! We have already seen that
it must be in quantity sufficient to sustain a platinum wire 1/104
of an inch in thickness, red hot, in contact with the air, for three
minutes and three quarters. It would appear that 800,000 charges of a
Leyden battery, charged by thirty turns of a very large and powerful
plate machine, in full action--a quantity sufficient, if passed at once
through the head of a rat or cat, to have killed it as by a flash of
lightning--are necessary to supply electricity sufficient to decompose
a single grain of water; or, if I am right, to equal the quantity of
electricity which is naturally associated with the elements of that
grain of water, endowing them with their mutual chemical affinity.”

[143] _Experimental Researches_: Faraday.

[144] The appearance of acid and alkaline matter, in water acted on
by a current of electricity, at the opposite electrified metallic
surfaces, was observed in the first chemical experiments made with
the column of Volta--(see Nicholson’s Journal, vol. iv. p. 183, and
vol. iv. p. 261, for Mr. Cruickshank’s Experiments; and Annales de
Chimie, tom. xxxvii. p. 233, for those of M. Desormes): _On some
Chemical Agencies in Electricity_: by Sir Humphry Davy.--Philosophical
Transactions for 1807. The various theories of electro-chemical
decomposition are carefully stated by Faraday, in his fifth series
of _Experimental Researches on Electricity_, in which he thus states
his own views:--“It appears to me that the effect is produced by an
_internal corpuscular action_ exerted according to the direction of
the electric current, and that it is due to a force either _superadded
to_ or _giving direction to the ordinary chemical affinity_ of the
bodies present. The body under decomposition may be considered as a
mass of acting particles, all those which are included in the course
of the electric current contributing to the final effect; and it is
because the ordinary chemical affinity is relieved, weakened, or partly
neutralized by the influence of the electric current in one direction
parallel to the course of the latter, and strengthened or added to in
the opposite direction, that the combining particles have a tendency to
pass in opposite courses.”

[145] “This capital discovery (chemical decomposition of electricity)
appears to have been made in the first instance by Messrs. Nicholson
and Carlisle, who observed the decomposition of water so produced. It
was speedily followed up by the still more important one of Berzelius
and Hisinger, who ascertained it as a general law, that, in all the
decompositions so effected, the acids and oxygen become transferred and
accumulated around the positive, and hydrogen, metals, and alkalies
around the negative, pole of a voltaic circuit; being transferred in
an invisible, and, as it were, a latent or torpid state, by the action
of the electric current, through considerable spaces, and even through
large quantities of water or other liquids, again to reappear with all
their properties at their appropriate resting-places.”--_Discourse on
the Study of Natural Philosophy_: by Sir John Herschel, Bart., F.R.S.

[146] Numerous beautiful illustrations of this fact will be found in
Becquerel’s _Traité Expérimental de l’Électricité et du Magnétisme_.

[147] See _Le Feu élémentaire_ of l’Abbé Nollet; Leçons de
Physique, tom. vi. p. 252; _Du Pouvoir thermo-électrique_, by M.
Becquerel--Annales de Chimie, vol. xli. p. 353; also a Memoir by
Nobili, Bibliothèque Universelle, vol. xxxvii. p. 15; _Experimental
Contributions towards the theory of Thermo-Electricity_ by Mr. J.
Prideaux--Philosophical Magazine, vol. iii., Third Series; _On the
Thermo-Magnetism of Homogeneous Bodies, with illustrative experiments_,
by Mr. William Sturgeon--Philosophical Magazine, vol. x. p. 1-116,
New Series. Botto made magnets and obtained chemical decomposition.
Antinori produced the spark. Mr. Watkins heated a wire in Harris’s
Thermo-Electrometer.

[148] A very ingenious application of the knowledge of this fact
was suggested by Mr. Solly, by which the heat of a furnace could be
constantly registered at a very considerable distance from it. See
_Description of an Electric Thermometer_: by E. Solly, Jun., Esq.
Philosophical Magazine, vol. xx. p. 391. New Series.

[149] Humboldt; _Personal Narrative_, Chap. xvii.--Annales de Chimie,
vol. xiv. p. 15.

[150] _Experimental Researches on Electricity._ Series xv.
Consult Sir Humphry Davy: _An Account of some Experiments on the
Torpedo_.--Philosophical Transactions, 1829, p. 15. John Davy, M.D.,
F.R.S.: _An Account of some Experiments and Observations on the
Torpedo_, ibid., 1832, p. 259; and the same author’s _Observations on
the Torpedo, with an Account of some Additional Experiments on its
Electricity_; and Matteucci, Bibliothèque Universelle, 1837, vol. xii.
p. 174.

[151] _On Lightning Conductors_, by Sir William Snow Harris;
_Observations on the Action of Lightning Conductors_, by W. Snow
Harris, Esq., F.R.S.--London Electrical Society’s Transactions.
Numerous valuable papers _On Electricity_, by Sir William Harris, will
be found in the Philosophical Transactions.

[152] Adopting, to a certain extent, this view, Faraday, in his
_Electrical Nomenclature_, proposed for the word pole to substitute
_anode_ (ανω, _upwards_, and ὁδος, _a way_), the way which the sun
rises; and _cathode_ (κατα, _downwards_, and ὁδος, _a way_), the way
which the sun sets. The hypothesis belongs essentially to Ampère.
_Objections to the Theories severally of Franklin, Dufay, and Ampère,
with an Effort to Explain Electrical Phenomena by Statical or
Undulatory Polarisation_, by Robert Hare, M.D., Pennsylvania, will well
repay an attentive perusal.

[153] _Inquiry into the Laws of the Vital Functions._--Philosophical
Transactions, 1815, 1822; _Some Observations relating to the Functions
of Digestion_, ibid., 1829: _On the Powers on which the Functions of
Life in the more perfect animals depend, and on the manner in which
they are associated in the production of their more complicated
results_, by A. P. W. Philip, M.D., F.R.S., L. and E.--The following
extract from the last-quoted of Dr. Philip’s Memoirs, will give a
general view of the conclusions of that eminent physiologist:--“With
respect to the nature of the powers of the living animal which we have
been considering, the sensorial and muscular powers, and the powers
peculiar to living blood, we have found belong to the living animal
alone, all their peculiar properties being the properties of life. The
functions of life may be divided into two classes, those which are
affected by the properties of this principle alone, and those, by far
the most numerous class, which result from the co-operation of these
properties with those of the principles which operate in inanimate
nature. The nervous power we have found to be a modification of one
of the latter principles, because it can exist in other textures than
those to which it belongs in the living animal, and we can substitute
for it one of those principles without disturbing the functions of life.

“Late discoveries have been gradually evincing how far more extensive
than was supposed, even a few years ago, is the dominion of
electricity. Magnetism, chemical affinity, and (I believe from the
facts stated in the foregoing paper, it will be impossible to avoid
the conclusion) the nervous influence, the leading power in the vital
functions of the animal frame, properly so called, appear all of them
to be modifications of this apparently universal agent; for I may add
we have already some glimpses of its still more extensive dominion.”

Refer to Dr. Reid’s papers.

[154] _Electro-physiological Researches_: by Signor Carlo Matteucci;
Phil. Trans. 1845, p. 293, and subsequent years.

[155] Electro-Biology: by Alfred Smee, Esq.

[156] _Observations of Electric Currents in Vegetable Structures_: by
Golding Bird, Esq., F.L.S.; Magazine of Natural History, vol. x. p.
240. In this paper Dr. Bird remarks that his experiments lead to the
conclusion that vegetables cannot become so charged with electricity
as to afford a spark; that electrical currents of feeble tension are
always circulating in vegetable tissues; and that electrical currents
are developed during germination from chemical action.

[157] _On Mineral Veins_: by Robert Were Fox, Esq.; Fourth Report
of the Royal Cornwall Polytechnic Society. _On the Electro-magnetic
Properties of Metalliferous Veins in the mines of Cornwall_: by Robert
W. Fox, Esq.; Phil. Trans. 1830, p. 399.

[158] _Experiments and Observations on the Electricity of Mineral
Veins_: by Robert Hunt and John Phillips; Reports of the Royal Cornwall
Polytechnic Society for 1841-42. _On the Electricity of Mineral Veins_:
by Mr. John Arthur Phillips; Ibid., 1843.

[159] In the lead lodes of _Lagylas_ and _Frongoch_, electrical
currents were detected by Mr. Fox, but none in those of _South Mold_
and _Milwr_, in Flintshire: Cornwall Geological Transactions, vol. iv.
In the lead veins of _Coldberry_ and _Skeers_, in Teasdale, Durham, the
currents detected were very feeble: Reports of the Bristol Association,
1838. Von Strombeck could detect no electric currents in the veins
worked in the clay slate near Saint Goar, on the Rhine: Archiv. für
Mineralogie, Geognosie, &c., von Dr. C. J. B Karsten, 1833. Professor
Reich, however, obtained very decided results at _Frisch Glück_,
_Neue Hoffnung_, _Gottlob_, and in other mineral veins in the mining
districts of Saxony: Edinburgh New Philosophical Journal, vol. xxviii.
1839. The irregularities are all to be explained by the presence or
absence of chemical excitation.

[160] This was remarkably the case at _Huel Sparnon_, near Redruth,
where the cobalt was discovered between two portions of a dislocated
lode; and the same was observed by Mr. Percival Johnson in a small mine
worked for nickel, near St. Austell.

[161] _On the process used for obtaining artificial veins in clay_: by
T. B. Jordan; Sixth Annual Report of the Royal Cornwall Polytechnic
Society. See also my memoir, already referred to, in the Memoirs of the
Geological Survey and Museum of Practical Geology, vol. i.

[162] See Becquerel, _Traité Experimental de l’Electricité, &c.
Electrical Experiments on the formation of Artificial Crystals_: by
Andrew Crosse, Esq.; British Association Reports, vol. v., 1836. The
lamination of clay and other substances is described in my memoir
referred to, Note p. 226.

[163] Report on the Geology of Cornwall, Devon, and West Somerset, by
Sir Henry T. De la Beche: _Theoretical observations on the formation
and filling of Mineral Veins and Common Faults_, p. 349.

[164] The following analyses of waters from deep mines were made by me
in 1840, and, with many others, published in the Reports of the Royal
Cornwall Polytechnic Society.

    Consolidated Mines, Gwennap,
               Cornwall.            In 1,000 grains of water.
        Muriate of soda                        1·5
        Sulphate of lime                        ·5
        Sulphate of iron                        ·15
        Sulphate of copper                     1·25
        Silica                                  ·15
        Alumina                                 ·3
                                               ----
            Total                              3·7

    United Mines, Gwennap.
        Muriate of soda                        1·10
        Muriate of lime                         ·15
        Sulphate of soda                        ·50
        Sulphate of lime                       1·5
        Sulphate of iron                        ·75
        Alumina                                 ·5
        Silica                                  ·15
                                               ----
            Total                              4·65

    Great St. George.
        Muriate of soda                        1·35
        Sulphate of lime                        ·74
        Carbonate of iron                       ·70
        Alumina                                 ·50
        Carbonate of lime                       ·10
                                               ----
            Total                              3·4

[165] The discovery of the electrotype has been disputed, as all
valuable discoveries are. Without, however, at all disparaging the
merits of what had been done by Mr. Jordan, I am satisfied, after
the most careful search, that the first person who really employed
electro-chemical action for the precipitation of metals in an
ornamental form, was Mr. Spencer, of Liverpool.

[166] See Spencer, _Instructions for the Multiplication of works of Art
in Metal by Voltaic Electricity. Novelties in Experimental Science_:
Griffin, Glasgow, _Elements of Electro-Metallurgy_: by Alfred Smee, Esq.

[167] The magneto-electrical machine is employed in Birmingham for this
purpose; but I am informed by Messrs. Elkington that they do not find
it economical, or rather that the electro-precipitation is carried on
too slowly.

[168] This has been done by Mr. Robert Were Fox, at a mine near
Falmouth. By connecting two copper wires with two lodes, and bringing
them, at the surface, into a cell containing a solution of sulphate
of copper, this gentleman obtained an electrotype copy of an engraved
copper-plate.

[169] This has been most effectually accomplished by Mr. Bain. Mr.
Hobson has had an electric clock, thus excited, in action for several
years.




CHAPTER X.

MAGNETISM.

  Magnetic Iron--Knowledge of, by the Ancients--Artificial
    Magnets--Electro-Magnets--Electro-Magnetism--Magneto-
    Electricity--Theories of Magnetism--The Magnetic Power of soft Iron
    and Steel--Influence of Heat on Magnetism--Terrestrial
    Magnetism--Declination of the Compass-needle--Variation of the
    Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly
    and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora
    Borealis--Magnetic Storms--Magnetic conditions of
    Matter--Diamagnetism, &c.


Agreeably with the view now generally received, that magnetism and
electricity are but modifications of one force, since they are found to
stand to each other in the relation of cause and effect, the separation
which is here adopted, of the consideration of their several phenomena,
may appear inappropriate. The importance, however, of all that is
connected with magnetism, and the very decided difference which is
presented by true magnetic action, and that of frictional or chemical
electricity, is so great that it has been thought advantageous to adopt
the present arrangement in reviewing the influence of terrestrial
magnetism with which science has made us acquainted.

From a very early period a peculiar attractive force has been observed
in some specimens of iron ore. Masses of this kind were found in
Magnesia, and from that locality we derive the name given to iron in
its polar condition. This is confirmed by the following lines by
Lucretius:--

    Quod superest agere incipiam, quo fœdere fiat
    Natura lapis hic ut ferrum ducere possit,
    Quem magnêta vocant patrio de nomine Graii
    Magnêtum, quia sit patriis in finibus ortus.

Again we find Pliny employing the term _magnetic_, to express this
singular power. It was known to the ancients that the magnetic power
of iron, and the electric property of amber, were not of the same
character, but they were both alike regarded as miraculous. The Chinese
and Arabians seem to have known Magnetism at a period long before
that at which Europeans became acquainted with either the natural
loadstone or the artificial magnet. Previously to A.D. 121, the magnet
is distinctly mentioned in a Chinese dictionary; and in A.D. 419 it
is stated in another of their books that ships were steered south by
it.[170]

The earliest popularly received account of its use in Europe is, that
Vasco de Gama employed a compass in 1427, when that really adventurous
navigator first explored the Indian seas. It is highly probable,
however, that the knowledge of its important use was derived from some
of the Oriental nations at a much earlier period.

We have some curious descriptions of the _leading stone_ or loadstone,
in the works of an Icelandic historian, who wrote in 1068. The
mariner’s compass is described in a French poem of the date of 1181;
and from Torfæus’s History of Norway, it appears to have been known to
the northern nations certainly in 1266.

We have not to deal with the history of magnetic discovery, but so
far as it tells of the strange properties which magnets are found to
possess, and the application of this knowledge to the elucidation of
effects occurring in nature.

A brown stone, in no respect presenting anything by which it shall be
distinguished from other rude stones around it, is found, upon close
examination, to possess the power of drawing light particles of iron
towards it. If this stone is placed upon a table, and iron filings
are thrown lightly around it, we discover that these filings arrange
themselves in symmetric curves, proceeding from some one point of the
mass to some other; and upon examining into this, we shall find that
the iron which has once clung to the one point will be rejected by the
other. If this stone is freely suspended, we shall learn also that
it always comes to rest in a certain position,--this position being
determined by these points, and some attractive force residing in the
earth itself. These points we call its poles; and it is now established
that this rude stone is but a small representative of our planet. Both
are magnetic: both are so in virtue of the circulation of currents
of electricity, or of lines of magnetic force, as seen in the curves
formed by the iron dust, and the north pole of the one attracts the
south pole of the other, and the contrary. By a confusion of terms we
speak of the north pole of a compass-needle, meaning that point which
is always opposite to the north pole of the earth: the truth being
that the pole of the compass-needle, which is so forcibly drawn to the
north, is a point in a contrary state, or, as we may express it, really
a south pole.

There is a power of a peculiar kind, differing from gravitation, or any
other attracting or aggregating force with which we are acquainted,
which exists permanently in the magnetic iron stones, and also in the
earth. What is this power?

Magnetism may be produced in any bar of steel, either by rubbing it
with a loadstone, or by placing it in a certain position in relation to
the magnetic currents of the earth, and, by a blow or any other means,
disturbing its molecular arrangement. This principle appears to involve
the iron as with an atmosphere, and to interpenetrate it. By one magnet
we may induce magnetism in any number of iron bars without its losing
any of its original force. As we have observed of the electrical forces
already considered, the magnet constantly presents two points in
which there is a difference manifested by the circumstance that they
are always drawn with considerable power towards the north or south
poles of the earth. That this power is of the same character as the
electricity which we have been considering, is now most satisfactorily
proved. By involving a bar of soft iron which, being without any
magnetic power, is incapable of sustaining even an ounce weight, with a
coil of copper wire, through which a galvanic current is passing, the
bar will receive, by induction from the current, an enormous accession
of power, and will, so long as the current flows around it, sustain
many hundred pounds weight, which, the moment the current is checked,
fall away from it in obedience to the law of gravity. Thus the mere
flow of this invisible agent around a mass of metal possessing no
magneto-attractive power, at once imparts this life-like influence to
it, and as long as the current is maintained, the iron is endowed with
this surprising energy.

This discovery, which we owe to the genius of Oersted, and which has,
indeed, given rise to a new science, electro-magnetism, may be regarded
as one of the most important additions made to our knowledge.

Current electricity is magnetic; iron is not necessary to the
production of magnetic phenomena, although by its presence we secure a
greater amount of power. The copper wires which complete the circuit
of a galvanic battery, will attract and hold up large quantities of
iron filings, and the wires of the electric telegraph will do the same,
while any signal is being conveyed along them. Again, all the phenomena
common to galvanic electricity can be produced by merely disturbing the
power permanently secured in the ordinary magnet. It was thought that
magnets would become weakened by this constant disturbance of their
magnetism; but, since its application to the purpose of manufacture,
and magneto-electricity has been employed in electro-plating, it has
been found that continued action for many years, during which enormous
quantities of electricity have been thus given out and employed in
producing chemical decomposition, has not, in the slightest degree,
altered their powers. Thus a small bar of metal is shown to be capable
of pouring out, for any number of years, the principle upon which the
phenomena of magnetism depend.

There are, however, differences, and striking ones, between ordinary
and magnetic electricity. In the magnet we have a power at rest, and in
the electrical machine or galvanic battery, a power in motion. Ordinary
electricity is stopped in its passage by a plate of glass, of resin,
and many other substances; but magnetism passes these with freedom, and
influences magnetic bodies placed on the other side. It would appear,
though we cannot explain how, that magnetism is due to some lateral
influence of the electric currents. A magnetic bar is placed over a
copper wire, and it hangs steadily in the direction of its length;
an electric current is passed along it, and the magnet is at once
driven to place itself across the wire. Upon this experiment, in the
main, Ampère founds his theory of terrestrial magnetism. He supposes
electrical currents to be traversing our globe from east to west, and
thus, that the needle takes its direction, not from the terrestrial
action of any fixed magnetic poles, but from the repulsion of these
currents, as is the case with the wire.

It has been found that wires, freely suspended, along which currents
were passing in opposite directions, revolve about each other, or have
an inclination to place themselves at right angles; thus exhibiting
the same phenomenon as the magnet and the conducting wire. So far the
hypothesis of Ampère leads us most satisfactorily. We see in the magnet
one form of electricity, and in the machine or battery another. But why
should not the electricity of the magnet, electricity at rest, exhibit
the same powers as this force in motion?

Oersted, whose theory led him to the discovery of the fact of the
magnetic power of an electric current, of the establishment indeed of
the new science--ELECTRO-MAGNETISM, regards the phenomena of a current
passing a wire, and its action on a needle, as evidence of two fluids,
positive and negative, traversing in opposite directions, and mutually
attracting and repelling. He conceives that they pass the wires in a
series of spirals; that in the magnet, by some peculiar property of the
iron, this conflict of the currents is reduced to an equilibrium, and
its power becomes manifested in its attractive force.[171] This does
not, however, convey a clear idea to the mind.

It is curious that iron becomes magnetic in a superior degree to any
other metal; that steel retains permanently any magnetism imparted
to it; but that soft iron rapidly loses its magnetic power. This
must be in virtue of some peculiar arrangement of the molecules, or
some unknown physical condition of the atoms of the mass, by which a
continued influence is retained by the steel, probably in a state of
constant internal circulation. It has, however, been shown that soft
iron, under certain circumstances, may be made to retain a large amount
of magnetic force.[172]

If a horse-shoe shaped bar of soft iron is rendered magnetic by the
circulation of an electric current around it, while its two ends are
united by an armature of soft iron, so that it is capable of supporting
many hundred pounds weight; and we then, by breaking the circuit, stop
the current, taking care the armature is kept in contact, the iron will
not lose its magnetic property, but will retain this power for many
years. If the connecting piece of iron, the armature, is removed, the
bar immediately loses all its magnetism, and will not support even the
armature itself. This fact appears to confirm the idea that magnetism
is due to the retention of electricity, and that steel possesses
the property of equalizing the opposing forces, or of binding this
principle to itself like an atmosphere.

The influence of heat on magnetism is so remarkable a proof of the
dependence of this power upon molecular arrangement, that it must not
escape our notice. To select but one of many experiments by Mr. Barlow,
it was found that in a bar of malleable iron, in which, when cold, the
magnetic effect was + 30° 0', all polarity ceased at a white heat, that
it was scarcely appreciable at a red heat, but that at a blood-red heat
it was equal to + 41° 0'.[173]

The more closely we examine the peculiarities of the magnetic power,
and particularly as they are presented to us in its terrestrial action,
the more surprising will its influence appear to be. We have discovered
a natural cause which certainly exercises a very remarkable power
over matter, and we have advanced so far in our investigations as to
have learnt the secret of converting one form of force into another,
or of giving to a principle, produced by one agency, a new character
under new conditions; of changing, in fact, electricity into magnetism,
and from magnetism again evolving many of the effects of electrical
currents.

If a magnetic bar is freely suspended above the earth, it takes,
in virtue of some terrestrial power, a given direction, which is
an indication of the earth’s magnetic force. Whether this is the
consequence of the currents of electricity, which Ampère supposes to
circulate around the globe, from east to west, or the result of points
of attraction in the earth itself, the phenomenon is equally wonderful.
To whatever cause we may refer the visible effects, it appears certain
that this earth is composed of particles in a magnetic state, the
character varying with physical conditions, and that terrestrial
magnetic force is the collective action of all the atoms of this
planetary mass.[174]

The remarkable connexion which has been observed between the changes
in the physical condition of the surface of the sun and terrestrial
phenomena, must not escape our notice. Sir William Herschel thought
he perceived a link connecting the dark spots on the sun’s face with
the variations of the earth’s temperature. This has not, however, been
confirmed by the observations which have been made since the time
of Herschel. The careful examinations of the solar spots which have
been made by Schwabe,[175] prove a well-defined order of progress in
them. He has discovered that they move in cycles of ten years--from
the smallest number visible in a given year, they regularly increase
for five years, when they reach their maximum; they then as regularly
decrease, and at the end of another five years they are at their
maximum number. The magnetic observations which have been carried on by
the British and other governments for some years, over every part of
the world, have elicited the fact that the order of variation in the
earth’s magnetic intensity is in cycles of ten years, and the law of
increase and decrease which is found to prevail with the solar spots
distinctly marks the variations of terrestrial magnetism. Few more
interesting facts than this are within the range of our knowledge,
proving as it does the direct dependence of terrestrial phenomena on
solar force.

The constancy with which a magnetised needle points along a certain
line which varies a little from the earth’s axial line, renders it one
of the most important instruments to the practical and the scientific
man. The wanderer of the ocean or of the desert is enabled, without
fear of error, to pursue his path, and in unknown regions to determine
the azimuth of objects. The miner or the surveyor finds in the
magnetic compass the surest guide in his labours, and the experiment is
for ever studying its indications.

    “True as the needle to the pole,”

has passed into a proverb among mankind, but the searching inquiry
of modern observers has shown that the expression is correct only
with certain limitations. There are two lines on the surface of the
earth along which the needle points true north, or where the magnetic
and the geographical north correspond. These are called lines of _no
variation_, or, as they have also been designated, _agonic lines_, and
one is found in the eastern and the other in the western hemisphere.
The American line is singularly regular, passing in a south-east
direction from the latitude 60° to the west of Hudson’s Bay, across the
American lakes, till it reaches the South Atlantic ocean, and cuts the
meridian of Greenwich in about 65° south latitude. The Asiatic line
of _no variation_ is very irregular, owing, without doubt, to local
interferences; it begins below New Holland, in latitude 60° south,
it bends westward across the Indian ocean, and from Bombay has an
inflection eastward through China, and then northward across the sea
of Japan, till it reaches the latitude of 71° north, when it descends
again southward, with an immense semicircular bend, which terminates in
the White Sea.

Hansteen has thought that there are two points in each hemisphere which
may be regarded as stronger and weaker poles on opposite sides of the
poles of revolution. These are called the magnetic poles of the earth,
or by Hansteen _magnetic points of convergence_. These four points are
considered to have a regular motion round the globe, the two northern
ones from west to east, and the two southern ones from east to west. By
the assistance of recorded observations, Hansteen has calculated the
periods of these revolutions to be as follows:--

    The weakest north pole in 860 years.
    The strongest north pole in 1746 years.
    The weakest south pole in 1304 years.
    The strongest south pole in 4609 years.

There are some points of speculation on which Hansteen has ventured
which have been smiled at as fanciful; but they may rather indicate
an amount of knowledge in the Brahminical and Egyptian priesthood,
beyond what we are usually disposed to allow them, and prove that their
observations of nature had led them to an appreciation of some of the
most remarkable harmonies of this mysterious creation.

The above terms are exceedingly near 864, 1246, 1728, 4320, and those
numbers are equal to the mystic number of the Indians, Greeks, and
Egyptians, 432 multiplied by 2, 3, 4, and 10. On these the ancients
believed a certain combination of natural events to depend, and,
according to Brahminical mythology, the duration of the world is
divided into four periods, each of 432,000 years. Again, the sun’s mean
distance from the earth is 216 radii of the sun, and the moon’s mean
distance 216 radii of the moon, each the half of 432. Proceeding with
this very curious examination, Hansteen says, 60 multiplied by 432
equals 15,920, the smallest number divisible at once by all the four
periods of magnetic revolution, and hence the shortest time in which
the four poles can complete a cycle, and return to their present state,
and _which coincides exactly with the period in which the precession
of the equinoxes will amount to a complete circle_, reckoning the
precession at a degree in seventy-two years.[176]

When we consider the phenomena of terrestrial magnetism carefully, it
appears to indicate the action of a power external to the earth itself,
and, as Hansteen conceives, having its origin from the action of the
sun, heating, illuminating, and producing a magnetic tension, in the
same manner as it produces electrical excitation and actino-chemical
action.

The movements of these magnetic poles have been the subject of
extensive and most accurate observation in every quarter of the globe.
In London, during 1657-1662, there was no magnetic variation; the
agonic line passing through it. The variation steadily increased,
until, in 1815, it amounted to 24° 15' 17", since which time it has
been slowly diminishing. In addition to this great variation, we
have a regular annual change dependent on the position of the sun,
in reference to the equinoctial and solstitial points, which was
discovered by Cassini, and investigated by Arago and others. Also a
diurnal variation, which movement appears to commence early in the
morning, moving eastward until half-past seven, A.M., when it begins
to move westward until two, P.M., when it again returns to the east,
and in the course of the night reaches the point from which it started
twenty-four hours before.

We have also remarkable variations in what is termed the _dip_ of
the needle. It is well known that a piece of unmagnetized steel, if
carefully suspended by its centre, will swing in a perfectly horizontal
position, but, if we magnetize this bar, it will immediately be drawn
downwards at one end. The force of the earth’s polarity, attracting the
dissimilar pole, has caused it to _dip_.

There is, in the neighbourhood of the earth’s equator, and cutting it
at four points, an irregular curve, called the magnetic equator, or
_aclinic_ line, where the needle balances itself horizontally. As we
proceed from this line towards either pole the dip increases, until,
at the north and south poles, the needle takes a vertical position.
The _intensity_ of the earth’s magnetism is also found to vary with
the position, and to increase in a proportion which corresponds very
closely with the dip. But the _intensity_ is not a function of the
dip, and the lines of equal intensity, _isodynamic lines_, are not
parallel to those of equal dip. We have already remarked on the diurnal
variation of the declination of the needle; we know, also, that there
exists a regular monthly and daily change in the magnetic intensity.
The greatest monthly change appears when the earth is in its perihelion
and aphelion, in the months of December and June,--a maximum then
occurs; and about the time of the equinoxes a minimum is detected.[177]

The daily variation of intensity is greatest in the summer, and least
in the winter. The magnetism is generally found to be at a minimum when
the sun is near the meridian; its intensity increasing until about six
o’clock, when it again diminishes.[178]

What striking evidences all these well-ascertained facts give of the
dependence of terrestrial magnetism on solar influence! and in further
confirmation of this view, we find a very remarkable coincidence
between the lines of equal temperature--the isothermal lines, and those
of equal dip and magnetic intensity.

Sir David Brewster first pointed out that there were in the northern
hemisphere two poles of maximum cold; these poles agree with the
magnetic points of convergence; and the line of maximum heat, which
does not run parallel to the earth’s equator, is nearly coincident with
that of magnetic power. Since Seebeck has shown us that electrical
and magneto-electrical phenomena can be produced by the action of heat
upon metallic bars, we have, perhaps, approached towards some faint
appreciation of the manner in which the solar calorific radiations may,
acting on the surface of our planet, produce electrical and magnetic
effects. If we suppose that the sun produces a disturbance of the
earth’s electricity along any given line, in all directions at right
angles to that line, we shall have magnetic polarity induced.[179] That
such a disturbance is regularly produced every time the sun rises, has
been sufficiently proved by many observers.

In 1750, Wargentin noticed that a very remarkable display of _Aurora
borealis_ was the cause of a peculiar disturbance of the magnetic
needle; and Dr. Dalton[180] was the first to show that the luminous
rays of the Aurora are always parallel to the dipping-needle,
and that the Auroral arches cross the magnetic meridian at right
angles. Hansteen and Arago have attended with particular care to
these influences of the northern lights, and the results of their
observations are:--

That as the crown of the Aurora quits the usual place, the
dipping-needle moves several degrees forward:--

That the part of the sky where all the beams of the Aurora unite, is
that to which a magnetic needle directs itself, when suspended by its
centre of gravity:--

That the concentric circles, which show themselves previously to the
luminous beams, rest upon two points of the horizon equally distant
from the magnetic meridian; and that the most elevated points of each
arch are exactly in this meridian.[181]

It does not appear that every Aurora disturbs the magnetic needle; as
Captains Foster and Back both describe very splendid displays of the
phenomenon, which did not appear to produce any tremor or deviation
upon their instruments.[182]

Some sudden and violent movements have been from time to time observed
to take place in suspended magnets; and since the establishment of
magnetic observatories in almost every part of the globe, a very
remarkable coincidence in the time of these agitations has been
detected. They are frequently connected with the appearance of Aurora
borealis; but this is not constantly the case. These disturbances
have been called _magnetic storms_; and over the Asiatic and European
continent, the islands of the Atlantic and the western hemisphere, they
have been proved to be simultaneous.

From observations made at Petersburg by Kupffer, and deductions drawn
from the observations obtained by the Magnetic Association, it appears
probable that these _storms_ arise from a sudden displacement in the
magnetic lines of the earth’s surface; but the cause to which this may
be due is still to be sought for.

In the brief and hasty sketch which has been given of the phenomena
of terrestrial magnetism, enough has been stated to show the vast
importance of this very remarkable power in the great operations
of nature. We are gradually reducing the immense mass of recorded
observations, and arriving at certain laws which are found to prevail.
Still, the origin of the force, whether it is strictly electrical,
whether it is the circulation of a magnetic fluid, or whether it is
merely a peculiar excitation of some property of matter, are questions
which are open for investigation.

In the beautiful Aurora borealis, with its trembling diffusive lights,
and its many- rays, we have what may be regarded as a natural
exhibition of magnetism, and we appear to have within our grasp the
explanation we desire. But we know not the secret of even these
extraordinary meteorological displays. If we pass an electric spark
from a machine through a long cylinder, exhausted of air as far as
possible, we have a mimic representation of the Northern Lights--the
same attenuation of brightness, almost dwindling into phosphorescence;
and by the slightest change of temperature we may produce that play
of colours which is sometimes so remarkably manifested in Aurora. Dr.
Dalton considered Aurora borealis _as a magnetic phenomenon, and that
its beams are governed by the earth’s magnetism_. We know that the arc
of light produced between the poles of a powerful galvanic battery is
readily deflected by a good magnet; and we have lately learned that
every vapour obeys the magnetic force.[183] It is, therefore, yet a
question for our consideration, does the earth’s magnetism produce
the peculiar phenomena of Aurora by acting upon electricity in a
state of glow? or have we evidence in this display of the circulation
of the magnetic fluid around our globe, manifesting itself by its
action on the ferruginous and other metallic matter, which Fusinieri
has proved to exist in the upper regions of our atmosphere.[184] That
magnetic radiations do exist, has been proved by Faraday, and that they
form lines of force perpendicular to the earth’s surface, has been
experimentally shown. Parallelograms of wire moved upon a central axis,
and connected with a galvanometer, give at every revolution indication
of an electric disturbance in all respects analogous to the production
of a current by moving wires in front of a steel magnet.

The alteration in the properties of heat, when it passes from the
radiant state into combination with matter, exhibits to us something
like what we may suppose occurs in the conversion of magnetism into
electricity or the contrary. We have a subtile agent, which evidently
is for ever busy in producing the necessary conditions of change in
this our earth: an element to which is due the development of many of
the most active powers of nature; performing its part by blending with
those principles which we have already examined; associating itself
with every form of matter; and giving, as we shall presently see, in
all probability, the first impulses to combination, and regulating the
forms of aggregating particles.

As electricity has the power of altering the physical conditions of
the more adherent states of matter, thus giving rise to variations
of form and modes of combination, so gross matter appears to alter
the character of this agency, and thus disposes it to the several
modifications under which we have already detected its presence.
We have mechanical electricity and chemical electricity, each
performing its great work in nature; yet both manifesting conditions
so dissimilar, that tedious research was necessary before they could
be declared identical. Magnetic electricity is a third form; all its
characteristics are unlike the others, and the office it appears to
perform in the laboratory of creation is of a different order from
that of the other states of electrical force. In the first two we have
decomposing and recombining powers constantly manifested--in fact,
their influences are always of a chemical character; but in the last it
appears we have only a directive power. It was thought that evidence
had been detected of a chemical influence in magnetism; it did appear
that sometimes a retarding force was exerted, and often an accelerating
one. This has been again denied, and we have arrayed in opposition to
each other some of the first names among European experimentalists.
The question is not yet to be regarded as settled; but, from long and
tedious investigation, during which every old experiment has been
repeated, and numerous new ones tried, we incline to the conclusion
that chemical action is not directly affected by magnetic power. It
is highly probable that magnetism may, by altering the structural
arrangement of the surface, vary the rate of chemical action; but this
requires confirmation.[185]

There is no substance to be found in nature existing independently of
magnetic power. But it influences bodies in different ways: one set
acting with relation to magnetism, like iron, and arranging themselves
along the line of magnetic force,--these are called magnetic bodies;
another set, of which bismuth may be taken as the representative,
always placing themselves at right angles to this line,--these are
called _diamagnetic bodies_.[186] This is strikingly shown by means of
powerful electro-magnets; but the magnetism of the earth is sufficient,
under proper care, to exhibit the phenomena.

Every substance in nature is in one or other of these conditions. The
rocks, forming the crust of the earth, and the minerals which are
discovered in them; the surface soil, which is by nature prepared as
the fitting habitation of the vegetable world, and every tree, shrub,
and herb which finds root therein, with their carbonaceous matter, in
all its states of wood, leaf, flower, and fruit; the animal kingdom,
from the lowest monad through the entire series up to man,--have, all
of them, distinct magnetic or diamagnetic relations.

“It is a curious sight,” says Dr. Faraday, “to see a piece of wood or
of beef, or an apple, or a bottle of water repelled by a magnet, or,
taking the leaf of a tree, and hanging it up between the poles, to
observe it take an equatorial position. Whether any similar effects
occur in nature among the myriads of forms which, upon all parts of its
surface, are surrounded by air, and are subject to the action of lines
of magnetic force, is a question which can only be answered by future
observation.”[187]

At present, the bodies which are known to exhibit decided
ferro-magnetic properties are the following, which stand arranged in
the order of their intensity:--

    Iron, Nickel, Cobalt, Manganese,
    Chromium, Cerium, Titanium,
    Palladium, Platinum, Osmium.

It is interesting to know that there are evidences that two bodies
which, when separate, are not magnetic, as iron is, become so when
combined. Copper and zinc are both of the diamagnetic class, but many
kinds of brass are discovered to be magnetic.

The salts of the above metals are, to a greater or less extent,
ferro-magnetic, but they may be rendered neutral by water, which is a
diamagnetic body, being repelled by the magnet. It will be unnecessary,
here, to enumerate the class of bodies which are diamagnetic; indeed,
all not included in the preceding list may be considered as belonging
to that class, with the exception of gases and vapours, which appear
to exist, relatively to each other, sometimes in the one, and sometimes
in the other condition.[188]

To endeavour to reduce our knowledge of these facts to some practical
explanation, we must bear in mind that particular spaces around the
north and south geographical poles of the earth, are regarded as
circles to which all the magnetic lines of force converge. Under
circumstances which should prevent any interference with what is called
ferro-magnetic action, all bodies coming under that class would arrange
themselves according to the laws which would regulate the disposition
of an infinite number of magnets, free to move within the sphere of
each other’s influence. The north and south pole of one magnetic body
would attach itself to the south and north pole of another, until we
had a line of magnets of any extent; the two ends being in opposite
states, like the magnetic points of convergence of the earth.

Every body, not ferro-magnetic, places itself across such a line of
magnetic force as we have conceived; and if the earth were made up of
separate layers of ferro-magnetic and diamagnetic bodies, the result
would be the formation of bands at right angles to each other. This
is not the case, by reason of the intermingling of the two classes
of substances. Out of the known chemical elements we find only about
ten which are actively ferro-magnetic; the others combining with
these give rise to either a weaker state, a neutral condition, or
the balance of action is turned to the diamagnetic side. Sulphate of
iron, for instance, is a magnetic salt; but in solution, water being
diamagnetic, it loses its property. The yellow prussiate of potash
dissolved in water is a diamagnetic body; but the red prussiate, which
contains an atom less of potassium, is magnetic: but in the solid state
they are both diamagnetic.[189]

From this it would appear that the chemical composition of a body
regulated its relation to magnetism. The following facts will show,
however, that the molecular structure is more particularly concerned in
determining the molecular condition of substances.

M. Plücker, being desirous of finding the extent to which the
_direction of the fibres_ in organic bodies might influence their
magnetic or diamagnetic properties, was led to inquire whether in
crystals the direction of the optic axes, which itself depends upon the
arrangement of the particles, might not also exercise some influence.
The first submitted to the action of the electro-magnet a thin plate
of tourmaline, such as is employed in experiments upon polarization,
having its optic axis parallel to its longest length. It was very
quickly perceived that the plate was magnetic, by the effect of the
iron that it contains; but it was suspended successively in three
ways,--first, so that its longest side was vertical, then as that the
shortest side was vertical, and finally so that the plate itself was
horizontal. In the first case it is directed between the two points
of the conical curvatures of the poles like a magnetic body; but, in
the other two cases, on the contrary, it took the direction assumed by
diamagnetic bodies--that is to say, a direction such that its longest
length was perpendicular to the line joining the poles. This direction
indicated that the optical axis was repelled by the two poles, and that
this repulsion outweighed the magnetic properties of the crystal.[190]

The relation of structure to physical phenomena of essentially
different characters is remarkable. Savart, when making crystalline
plates of quartz and carbonate of lime vibrate, succeeded in
determining a relation between the acoustic figures that are
produced in them, and the particular mode of the crystallization of
the substance. He found that the direction of the optical axis is
constantly connected with that of the principal forms of the acoustic
figures.

Mitscherlich has remarked that crystals do not expand uniformly by
heat, but that this dilatation is greater in one direction than in
another; and that this difference is connected with their crystalline
form. M. de Sénarmont has shown that conductibility for heat,
which is equal in all directions for the crystals of the regular
system, acquires in others a maximum or a minimum value, according
to directions parallel to the crystallographic axes; so that the
isothermic surfaces, which are spheres in the former case, are, in the
other, ellipsoids elongated or flattened in the same direction. The
optical axes do not altogether coincide with the principal axes of
conductibility for heat; but this appears to be due merely to slight
differences in the rate of progression, or the refrangibility of the
luminous and calorific rays.

Wiedemann, by employing a fine point through which he made electricity
arrive upon a surface that he had powdered with licopodium or red lead,
succeeded in determining, by means of the form assumed by this light
powder, the conductibility of crystals in different directions.

On a surface of glass, the powder which disperses itself around the
points, in consequence of electric repulsion, forms a circular
figure traversed by radii. When a plate of gypsum is used instead of
glass the figure is found to be elliptical, and the great axis of
the ellipse forms a right angle with the principal crystallographic
axis, which proves that the electricity distributes itself more
easily in a direction perpendicular to the axis than in any other.
M. Wiedemann comes to the conclusion that crystals which possess a
better conductibility in the direction of the principal axis, all
belong to the class of negative crystals: while those which have a
better conductibility in the direction perpendicular to the axis are
positive, which indicates that the direction of best conductibility
for electricity is also that according to which light is propagated
relatively with greater velocity.

Tyndale has shown, that if gutta percha which has been rendered fibrous
in manufacture is cut so that the fibres are in the direction of this
greatest length, or in a direction perpendicular to this greatest
length, and placed under the influence of a magnet, they direct
themselves equatorially. Ivory cut in the same direction manifests the
same conditions, though both these substances are diamagnetic.

The fibrous structure, and the planes of cleavage, thus determine the
magnetic condition of a substance. The special properties presented by
crystals, in regard to the action exercised upon them by magnets, is
due to a particular mode of grouping their particles. This is also the
cause of unequal dilatability, and of unequal conductibility for heat
and for electricity.

How curiously, therefore, does molecular structure determine the
relation of a body to any of the forms of physical force!

We still search in the dark, and see but dimly the evidences; yet it
becomes almost a certainty to us, that this stone of granite, with its
curious arrangement of felspar, mica, and quartz, presents its peculiar
condition in virtue of some law of magnetic force. The crystal, too,
of quartz, which we break out of the mass, and which presents to us a
beautifully regular figure, is, beyond a doubt, so formed, because the
atoms of silica are each one impelled in obedience to one of these two
conditions of magnetism to set themselves in a certain order to each
other, which cannot be altered by human force without destruction.

All the laws which regulate the forms of crystals and amorphous bodies
are, to the greatest degree, simple. In nature the end is ever attained
by the easiest means; and the complexity of operation, which appears
sometimes to the observer, is only so because he cannot see the spring
by which the machine is moved.

The gaseous envelope, our atmosphere, is in a neutral state. Oxygen is
strikingly magnetic in relation to hydrogen gas, whilst nitrogen is as
singularly the contrary; and the same contrasts present themselves when
these gases are examined in their relation to common air. Thus, oxygen
being magnetic, and nitrogen the contrary, we have an equilibrium
established, and the result is a compound neutral in its relations to
all matter. All gases and vapours are found to be diamagnetic, but in
different degrees.[191] This is shown by passing a stream of the gas,
rendered visible by a little smoke, within the influence of a powerful
magnet.

These bodies are, however, found relatively to each other,--or even
to themselves, under different thermic conditions,--to change their
states, and pass from the magnetic to the diamagnetic class. Heat has a
very remarkable influence in altering these relations; and atmospheric
air at one temperature is magnetic to the same fluid at another: thus,
by thermic variations, attraction or repulsion may be alternately
maintained. By this it must be understood that a stream of air, at a
temperature elevated but a few degrees above that of an atmosphere of
the same kind into which it is passing, is deflected in one way by a
magnet; whereas, if the stream is colder than the bulk through which
it flows, it is bent in another way by the same force. In this respect
magnetism and diamagnetism show equally the influence of another
physical force, heat; and we may safely refer many meteorological
phenomena to similar alterations of condition in the atmosphere,
relative to the magnetic relations of the aërial currents.

That magnetism has a directive power is satisfactorily shown by
the formation of crystals in the neighbourhood of the poles of
powerful magnets. The common iron salt, the protosulphate, ordinarily
crystallizes so that the crystals unite by their faces; but when
crystallizing under magnetic influence, they have a tendency to arrange
themselves with regard to each other so that the acute angle of one
crystal unites with one of the faces of another crystal, near to, but
never actually at, its obtuse angle. In addition to this, if a magnet
of sufficient power is employed, the crystals arrange themselves in
magnetic curves from one pole to the other, a larger crop of crystals
being always formed at the north than at the south pole. Here we have
evidence of an actual turning round of the crystal, in obedience to the
directive force of the magnet; and we have the curious circumstance of
a difference in some way, which is not clearly explained, between the
two opposite poles. If, instead of an iron or a ferro-magnetic salt,
we employ one which belongs to the other, or diamagnetic, class, we
have a curious difference in the result. If into a glass dish, fixed
on the poles of a strong electro-magnet, we pour a quantity of a
solution of nitrate of silver, and place in the fluid, over the poles
of the magnet, two globules of mercury (an arrangement by which that
arborescent crystallization, called the _Arbor Dianæ_, is produced,) we
have the long needle-shaped crystals of silver, arranging themselves in
curves which would cut the ordinary magnetic lines at right angles.[192]

In the first example given we have an exhibition of magnetic force,
while in the last we have a striking display of the diamagnetic power.

The large majority of natural formations appear to group themselves
under the class of diamagnetics. These bodies are thought to possess
poles of mutual repulsion among themselves, and which are equally
repelled by the magnetic points of convergence. Confining our ideas to
single particles in one condition or the other, we shall, to a certain
extent, comprehend the manifold results which must arise from the
exercise of these two modes of force. At present, our knowledge of the
laws of magnetism is too limited to allow of our making any general
deductions relative to the disposition of the molecules of matter; and
the amount of observation which has been given to the great natural
arrangements, is too confined to enable us to infer more than that it
is probable many of the structural conditions of our planet are due to
polarity.

Mountain ranges observe a singular uniformity of direction, and
the cleavage planes of rock are evidently determined by some
all-pervading power. Mineral bodies are not distributed in all
rocks indiscriminately. The primary formations hold one class of
metalliferous ores, and the more recent ones another. This is not
to be regarded as in any way connected with their respective ages,
but with some peculiar condition of the stone itself. The granite
and slate rocks, at their junctions, present the required conditions
for the deposit of copper ore, while we find the limestones have the
characteristic physical state for accumulating lead ore. Again, on
examining any mineral vein, it will be at once apparent that every
particle of ore, and every crystal of quartz or limestone, is disposed
in a direction which indicates the exercise of some powerful directive
agency.[193]

It appears, from all the results hitherto obtained, that the magnetic
and diamagnetic condition of bodies is equally due to some peculiar
property of matter in relation to the other forms of electricity. We
have not yet arrived at the connecting link, but it does not appear to
be far distant.

We have already referred to the statement made by talented
experimentalists, that magnetism has a powerful influence in either
retarding or accelerating chemical combination. Beyond a doubt chemical
action weakens the power of a magnet; but the disturbance which it
occasions in soft iron, on the contrary, appears to tend to its
receiving magnetism more readily, and retaining it more permanently.
Further investigations are, however, required, before we can decide
satisfactorily either of these problems, both of which bear very
strongly upon the subject we have just been considering.

We have seen that heat and electricity act strangely on magnetic force,
and that this statical power reacts upon them: and thus the question
naturally arises, Do light and magnetism in any way act upon each other?

Morichini and Carpi on the continent, and Mrs. Somerville in England,
have stated that small bars of steel can be rendered magnetic by
exposing them to the influence of the violet rays of light. These
results have been denied by others, but again repeated and apparently
confirmed. In all probability, the rays to which the needles were
exposed, being those in which the maximum actinic power is found,
produced an actual chemical change; and then, if the position were
favourable, it is quite evident that magnetism would be imparted.
Indeed we have found this to be the case when the needles, exposed to
solar radiations, were placed in the direction of the dip. The supposed
magnetization of light by Faraday has already been mentioned. If the
influence in one case is determined, it will render the other more
probable.[194]

“In seeking for a cause,” writes Sir David Brewster, “which is capable
of inducing magnetism on the ferruginous matter of our globe, whether
we place it within the earth, or in its atmosphere, we are limited to
the SUN, to which all the magnetic phenomena have a distinct reference;
but, whether it acts by its heat, or by its light, or by specific
rays, or influences of a magnetic nature, must be left to future
inquiry.”[195]

We have learnt that magnetism is not limited to ferruginous matter; we
know that the ancient doctrine of the universality of the property is
true. Kircher, in his strange work on Magnetism, published in the early
part of the seventeenth century[196]--a curious exemplification of the
most unwearying industry and careful experiment, combined with the
influences of the credulity and superstitions of his age--attributes to
this power nearly all the cosmical phenomena with which, in his time,
men were acquainted. He curiously anticipates the use of the supposed
virtue of magnetic traction in the curative art; and as the titles of
his concluding chapters sufficiently show, he was a firm believer in
animal magnetism.[197] But it is not with any reference to these that
we refer to the work of _Athanasii Kircheri, Societatis Jesu, Magnes,
sive de Magnetivâ Arte_, but to show that two hundred years since,
man was near a great truth; but the time of its development being not
yet come, it was allowed to sleep for more than two centuries, and
the shadow of night had covered it. In speaking of the vegetable
world, and the remarkable processes by which the leaf, the flower,
and the fruit are produced, this sage brings forward the fact of the
diamagnetic character of the plant, which has been, within the last two
years, re-discovered; and he refers the motions of the Sun-flower, the
closing of the Convolvulus, and the directions of the spiral, formed by
twining plants, to this particular influence.

This does not appear as a mere speculation, a random guess, but is
the result of deductions from experiment and observation. Kircher
doubtless leaped over a wide space to come to his conclusion; but the
result is valuable in a twofold sense. In the first it shows us that,
by neglecting a fact which is suggestive, we probably lose a truth
of great general application; and secondly, it proves to us, that by
stepping beyond the point to which inductive logic leads, and venturing
on the wide sea of hypothesis, we are liable to sacrifice the true to
the false, and thus to hinder the progress of human knowledge.

Magnetism, in one or other of its forms, is now proved to be universal,
and to its power we are disposed to refer the structural conditions
of all material bodies, both organic and inorganic. This view has
scarcely yet been recognised by philosophers; but as we find a certain
law of polarity prevailing through every atom of created matter, in
whatever state it may be presented to our senses, it is evident that
every particle must have a polar and directing influence upon the mass,
and every coherent mass becomes thus only a larger and more powerful
representative of the magnetic unit. Thus we see the speculation of
Hansteen, that the sun is, to us, a magnetic centre, and that it
is equally influenced by the remoter suns of the universe,[198] is
supported by legitimate deductions from experiment.

The great difficulty is not, however, got rid of by this speculation;
the cause by which the earth’s magnetism is induced is only removed
further off.

The idea of a magnetic fluid is scarcely tenable; and the ferruginous
nature of the Aurora borealis receives no proof from any investigation;
indeed, we have procured evidence to show that iron is not at all
necessary for the production of magnetic phenomena. The leaf of a
tree, a flower, fruit, a piece of animal muscle, glass, paper, and a
variety of similar substances, have the power of repelling the bar of
iron which we call a magnet, and of placing it at right angles to the
direction of the force exerted by them. This is a point which must be
constantly borne in mind when we now consider the mysteries of magnetic
phenomena.

Any two masses of matter act upon each other according to this law,
and although by the power of cohesion the force may be brought to an
equilibrium, or to its zero point, it is never lost, and may be readily
and rapidly manifested by any of the means employed for electrical
excitation.

Reasoning by analogy, the question fairly suggests itself: If two
systems of inorganic atomic constitution are thus invested with a
power of influencing each other through a distance, why may not
two more highly developed organic systems equally, or to a greater
extent, produce an influence in like manner? Upon such reasoning as
this is founded the phenomenon known as Animal Magnetism. There is no
denying the fact that one mass of blood, muscle, nerves, and bone,
must, magnetically, influence another similar mass. This is, however,
something totally different from that abnormal condition which is
produced through some peculiar and, as yet, unexplained physiological
influences.

With the mysterious operations of vital action, the forces which we
have been considering have nothing whatever in common. The powers
which are employed in the arrangements of matter are, notwithstanding
their subtile character, of far too gross a nature to influence the
psychological mysteries which present themselves to the observant
mind. It cannot be denied that, by placing a person of even moderate
nervous sensibility in a constrained position, and under an unnatural
influence of the mind, as acquired by the disciples of Mesmer, a torpor
affecting only certain senses is produced. The recognised and undoubted
phenomena are in the highest degree curious--but in these the marvels
of charlatanry and ignorance are not included;--and the explanation
must be sought for by the physiologist among those hidden principles
upon which depends all human sensation.[199]

Man, like a magician, stands upon a promontory, and surveying the great
ocean of the physical forces which involve the material creation,
and produce that infinite variety of phenomena which is unceasingly
exhibited around him, he extends the wand of intelligence, and bids the
“spirits of the vasty deep” obey his evocation.

The phenomena recur--the great processes of creation go on--the
external manifestations of omnipotent power proceed--effects are
again and again produced; but the current of force passes undulating
onwards;--and to the proud bidding of the evocator there is no reply
but the echo of his own vain voice, which is lost at last in the vast
immensity of the unknown which lies beyond him.

We see how powerfully the physical forces, in their various modes of
action, stir and animate this planetary mass; and amongst these the
influence of magnetism appears as a great directing agent, though its
origin is unknown to us.

    That power which, like a potent spirit, guides
    The sea-wide wanderers over distant tides,
    Inspiring confidence where’er they roam,
    By indicating still the pathway home;--
    Through nature, quicken’d by the solar beam,
    Invests each atom with a force supreme,
    Directs the cavern’d crystal in its birth,
    And frames the mightiest mountains of the earth;
    Each leaf and flower by its strong law restrains,
    And binds the monarch Man within its mystic chains.


FOOTNOTES:

[170] _Treatise on Magnetism_, by Sir David Brewster. _Cosmos: a
Sketch of a Physical description of the Universe_; by Alexander Von
Humboldt.--Otté’s Translation.

[171] _Expérience Electro-Magnétique._ par M. Œrsted.--Annales de
Chimie, vol. xxii. p. 201. De la Rive, _Recherches sur la Distribution
de l’Electricité dyn. dans les Corps_.--Genève, 1825.

[172] _On the Magnetic power of Soft Iron_: by Mr.
Watkins.--Philosophical Transactions, 1833.

[173] Cavallo, _On Magnetism_.--Cavallo was the first who noticed the
influence of heat on Magnetism. Consult _On the anomalous Magnetic
Action of Hot Iron between the white and blood-red heat_: by Peter
Barlow, Esq.--Philosophical Transactions, 1822, p. 124. _Treatise on
Magnetism_: by Barlow.--Encyclopædia Metropolitana.

[174] “The foundation of our researches is the assumption that the
terrestrial magnetic force is the collective action of all the
magnetised particles of the earth’s mass. We represent to ourselves
magnetisation as the separation of the magnetic fluids. Admitting the
representation, the mode of action of the fluids (repulsion of similar,
and attraction of dissimilar, particles inversely as the square of the
distance) belongs to the number of established truths. No alteration
in the results would be caused by changing this mode of representation
for that of Ampère, whereby, instead of magnetic fluids, magnetism is
held to consist in constant galvanic currents in the minutest particles
of bodies. Nor would it occasion a difference if the terrestrial
magnetism were ascribed to a mixed origin, as proceeding partly from
the separation of the magnetic fluids in the earth, and partly from
galvanic currents, in the same; inasmuch as it is known that for each
galvanic current may be substituted such a given distribution of the
magnetic fluids in a surface bounded by the current, as would exercise
in each point of external space precisely the same magnetic action as
would be produced by the galvanic current itself.”--_General Theory
of Terrestrial Magnetism_, by Professor Carl Friedrich Gauss, of the
University of Göttingen.--Scientific Memoirs, vol. ii. p. 188.

[175] Humboldt’s _Cosmos_.--Otté’s translation.

[176] Hansteen: _Untersuchungen über den Magnetismus der
Erde_, Christïana, 1819. Humboldt: _Exposé des Variations
Magnétiques_.--Gilbert’s Annales. Brewster’s Magnetism: Encyclopædia
Metropolitana.

[177] Hansteen; as above.

[178] _On the effects of temperature on the intensity of magnetic
forces, and on the diurnal variations of the terrestrial magnetic
intensity_; by Samuel Hunter Christie, Esq.--Philosophical
Transactions, vol. cxv. 1825.

[179] It has been observed by Mr. Barlow, in England, and some eminent
observers in Austria, that an electric current constantly traverses
the wires of the electric telegraph wherever there are two earth
connections.

[180] _Meteorological Observations and Essays_: by Dr. Dalton. _On the
Height of the Aurora Borealis above the surface of the Earth_: by John
Dalton, F.R.S.--Philosophical Transactions, vol. cxiv. p. 291.

[181] Arago: Annales de Chimie, vol. xxxix. p. 369. _On the variable
Intensity of Terrestrial Magnetism and the Influence of the Aurora
Borealis upon it_; by Robert Were Fox.--Philosophical Transactions,
1831, p. 199.

[182] “Brilliant and active coruscations of the Aurora Borealis,” says
Captain Back, “when seen through a hazy atmosphere, and exhibiting
the prismatic colours, almost invariably affected the needle. On the
contrary, a very bright Aurora, though attended by motion, and even
tinged with a dullish red and a yellow in a clear blue sky, seldom
produced any sensible change, beyond, at the most, a tremulous motion.
A dense haze or fog, in conjunction with an active Aurora, seemed
uniformly favourable to the disturbance of the needle, and a low
temperature was favourable to brilliant and active coruscations. On
no occasion during two winters was any sound heard to accompany the
motions. The Aurora was frequently seen at twilight, and as often to
the eastward as to the westward; clouds, also, were often perceived
in the day-time, in form and disposition very much resembling the
Aurora.”--_Narrative of the Arctic Land Expedition._

[183] Faraday: _On the Diamagnetic character of Flame and Gases_.

[184] “The Aurora Borealis is certainly in some measure a magnetical
phenomenon; and if iron were the only substance capable of exhibiting
magnetic effects, it would follow that some ferruginous particles
must exist in the upper regions of the atmosphere. The light usually
attending this magnetical meteor may possibly be derived from
electricity, which may be the immediate cause of a change in the
distribution of the magnetic fluid, contained in the ferruginous
vapours which are imagined to float in the air.”--Lecture on Magnetism:
Young’s _Lectures on Natural Philosophy_, p. 533.

[185] _On the supposed influence of Magnetism and Chemical Action_; by
Robert Hunt.--Philosophical Magazine, vol. xxxii. No. 215, 1849.

[186] Those bodies which are attracted by a magnet, as iron is, are
called _magnetic bodies_. Those which are, on the contrary, repelled by
the same power, are termed _diamagnetic bodies_. On these Dr. Faraday
remarks:--“Of the substances which compose the crust of the earth, by
far the greater portion belong to the diamagnetic class; and though
ferruginous and other magnetic matters, being more energetic in their
action, are more striking in their phenomena, we should be hasty in
assuming that, therefore, they over rule entirely the effect of the
former bodies. As regards the ocean, lakes, rivers, and the atmosphere,
they will exert their peculiar effect almost uninfluenced by any
magnetic matter in them, and as respects the rocks and mountains, their
diamagnetic influence is perhaps greater than might be anticipated.
I mentioned that by adjusting water and a salt of iron together, I
obtained a solution inactive in air; that is, by a due association
of the forces of a body, from each class, water and a salt of iron,
the magnetic force of the latter was entirely counteracted by the
diamagnetic force of the former, and the mixture was neither attracted
nor repelled: To produce this effect, it required that more than 48·6
grains of crystallised protosulphate of iron should be added to ten
cubic inches of water (for these proportions gave a solution which
would set equatorially), a quantity so large, that I was greatly
astonished on observing the power of the water to overcome it. It
is not, therefore, at all unlikely that many of the masses which
form the crust of this our globe, may have an excess of diamagnetic
power, and act accordingly.”--_On new magnetic actions, and on the
magnetic condition of all matter_; by Michael Faraday, D.C.L., F.R.S.,
&c.--Philosophical Transactions, Jan. 1846, vol. cxxxvii. p. 41.

[187] Ibid.

[188] _On the Diamagnetic conditions of Flame and Gases_, by Michael
Faraday. F.R.S.; and _On the motions presented by Flame when under
Electro-Magnetic Influence_, by Professor Zantedeschi.--Philosophical
Magazine, 1847, pp. 401-421.

[189] _On Diamagnetism_; by Professor Plücker, of Bonn.--Philosophical
Magazine, July, 1848.

[190] For a detailed account of the experiments of Faraday, Plücker,
Becquerel, Tyndale, and Knoblauch, see De La Rive’s _Treatise on
Electricity in Theory and Practice_.

[191] A few examples taken from Dr. Faraday’s paper will show this:--

Nitrogen being acted on was manifestly diamagnetic in relation to
common air when both were of the same temperature. Oxygen appears to
be magnetic in common air. Hydrogen proved to be clearly and even
strongly diamagnetic. Its diamagnetic state shows, in a striking
point of view, that gases, like solids, have peculiar and distinctive
degrees of diamagnetic force. Carbonic acid gas is diamagnetic in air.
Carbonic oxide was carefully freed from carbonic acid before it was
used, and it appears to be more diamagnetic than carbonic acid. Nitrous
oxide was moderately, but clearly, diamagnetic in air. Olefiant gas
was diamagnetic. The coal gas of London is very well diamagnetic, and
gives exceedingly good and distinct results. Sulphurous acid gas is
diamagnetic in air. Muriatic acid gas was decidedly diamagnetic in
air.--_On the Diamagnetic Conditions of Flame and Gases_: Philosophical
Magazine, 1847, p. 409.

[192] For illustration of this I must refer to my own Memoir,
_Researches on the Influence of Magnetism and Voltaic Electricity on
Crystallization, and other conditions of matter_, in the Memoirs of the
Geological Survey of Great Britain, &c., vol. i.

[193] In a work published by Mr. Evan Hopkins, entitled _On the
Connexion of Geology with Terrestrial Magnetism_, will be found many
valuable practical observations made in this country and the gold and
silver districts of America; but the views taken by the author are open
to many objections.

[194] See a notice by Faraday of Morichini’s Experiments in _Relations
of Light to Magnetic Force_--Philosophical Transactions, vol. cxxxvii.
p. 15. See also Mr. Christie _On Magnetic Influence in the Solar
Rays_--Philosophical Transactions, vol. cvii. p. 219; vol. cxix. p. 379.

[195] Sir David Brewster _On Magnetism_; republished from the
Encyclopædia Britannica.

[196] The whole of the title of Kircher’s book will convey some idea
of the subjects embraced:--Athanasii Kircheri Societatis Jesu Magnes,
sive de Arte Magneticâ; opus tripartitum, quo Universa Magnetis Natura
ejusque in omnibus Scientiis et Artibus usus novâ methodo explicatur:
ac præterea e viribus et prodigiosis effectibus Magneticarum aliarumque
abditarum Naturæ Motionum in Elementis, Lapidibus, Plantis, Animalibus
elucescentium: multa hucusque incognita Naturæ Arcana, per Physica,
Medica, Chymica, et Mathematica omnis generis Experimenta recluduntur
Editio Tertia: ab ipso Authore recognita emendataque, ac multis novorum
Experimentorum Problematibus aucta. Romæ, 1654.

[197] The following are the titles of the concluding chapters of
Kircher’s book:--_De magnetismo solis et lunæ in maria._ _De magneticâ
vi plantarum._ _De insitionis magneticis miraculis._ _De magnetismo
virgulæ auriferæ seu divinatoriæ._ _De plantis heliotropiis eorumque
magnetismo._ _De magnetismo rerum medicinalium._ _De vi attractivâ
potentiæ imaginativæ._ _De magnetismo musicæ._ _De magnetismo amoris._

[198] “For these reasons it appears most natural to seek their origin
in the sun, the source of all living activity, and our conjecture gains
probability from the preceding remarks on the daily oscillations of
the needle. Upon this principle the sun may be conceived as possessing
one or more magnetic axes, which, by distributing the force, occasion
a magnetic difference in the earth, in the moon, and all those planets
whose internal structure admits of such a difference. Yet, allowing
all this, the main difficulty seems not to be overcome, but merely
removed from the eyes to a greater distance; for the question may still
be asked, with equal justice, whence did the sun acquire its magnetic
force? And if from the sun we have recourse to a central sun, and from
that again to a general magnetic direction throughout the universe,
having the Milky Way for its equator, we but lengthen an unrestricted
chain, every link of which hangs on the preceding link, no one of them
on a point of support. All things considered, the following mode of
representing the subject appears to me most plausible. If a single
globe were left to move alone freely in the immensity of space, the
opposite forces existing in its material structure would soon arrive
at an equilibrium conformable to their nature, if they were not so at
first, and all activity would soon come to an end. But if we imagine
another globe to be introduced, a mutual relation will arise between
the two; and one of its results will be a reciprocal tendency to
unite, which is designated and sometimes thought to be explained by
the merely descriptive word Attraction. Now would this tendency be
the only consequence of this relation? Is it not more likely that the
fundamental forces, being drawn from their state of indifference or
rest, would exhibit their energy in all possible directions, giving
rise to all kinds of contrary action? The electric force is excited,
not by friction alone, but also by contact, and probably also, though
in smaller degrees, by the mutual action of two bodies at a distance;
for contact is nothing but the smallest possible distance, and that,
moreover, only for a few small particles. Is it not conceivable that
magnetic force may likewise originate in a similar manner? When the
natural philosopher and the mathematician pay regard to no other effect
of the reciprocal relation between two bodies at a distance, except
the tendency to unite, they proceed logically, if their investigations
require nothing more than a moving power; but should it be maintained
that no other energy can be developed between two such bodies, the
assertion will need proof and the proof will be hard to find.”--The
above is a translation from Hansteen’s work _On Magnetism_.

[199] See article _Animal Magnetism_, Encyclopædia Britannica, and Mr.
Braid’s papers _On Hypnotism_, published in the “Medical Times.”




CHAPTER XI.

CHEMICAL FORCES.

  Nature’s Chemistry--Changes produced by Chemical Combination--Atomic
    Constitution of Bodies--Laws of Combination--Combining
    Equivalents--Elective Affinity--Chemical Decomposition--Compound
    Character of Chemical Phenomena--Catalysis or action
    of Presence--Transformation of Organic Bodies--Organic
    Chemistry--Constancy of Combining Proportions--The Law of Volumes,
    the Law of Substitutions, Isomeric States, &c.


All things on the earth are the result of chemical combination. The
operations by which the commingling of molecules and the interchange
of atoms take place, we can imitate in our laboratories; but in nature
they proceed by slow degrees, and, in general, in our hands they are
distinguished by suddenness of action. In nature chemical power is
distributed over a long period of time, and the process of change is
scarcely to be observed. By art we concentrate chemical force, and
expend it in producing a change which occupies but a few hours at most.
Many of the more striking phenomena of nature are still mysterious to
us, and principally because we do not, or cannot, take the element time
into calculation. The geologist is compelled to do this to explain the
progress of the formation of the crust of the earth, but the chemist
rarely regards the effects of time in any of his operations. The
chemical change which within the fissure of the rock is slowly and
silently at work, displacing one element or molecule, and replacing it
by another, is in all probability the operation of a truly geological
period. Many, however, of the changes which are constantly going on
around us, are of a much more rapid character, and in these nature is
no slower in manipulating than the chemist.

Had it been that the elements which are now found in combination
could exist in a free state, the most disastrous consequences would
necessarily ensue. There must have been a period when many of the
combinations known to us were not yet created. Their elements either
existed in other forms, or were uncombined. Our rocks are compounds of
oxygen with certain peculiar metals which unite with oxygen so rapidly
that incandescence is produced by their combination. Let us suppose
that any of these metals existed in purity, and that they were suddenly
brought into contact with water, the atmospheric air, or any body
containing oxygen, the result would be a convulsion of the most fearful
kind; the entire mass of metal would glow with intensity of heat, and
the impetuosity of the action would only be subdued when the whole
of the metal had become oxidized. Volcanic action has been referred
to some such cause as this, but there is not sufficient evidence to
support the hypothesis; indeed, it is contrary to the opinion of most
philosophers.[200] Such a condition may possibly have existed at one
time, during that period when darkness was upon the face of the deep,
when the earth was a chaos; but it is only adduced here as an example
of the violent nature of some chemical changes. Potassium thrown on
water bursts into flame, and sodium does so under certain conditions.
If these, or the metals proper in a state of fine division, are brought
into an atmosphere of chlorine, the intensity of chemical action is so
great that they become incandescent, many of them glowing with extreme
brilliancy. If hydrogen gas is mixed with this element (chlorine)
they unite, under the influence of light, with explosive violence,
giving rise to a compound, muriatic acid, which combines with water
in an almost equally energetic manner. Nitrogen, as it exists in the
atmosphere, mixed with oxygen, appears nearly inert; with hydrogen it
forms the pungent compound, ammonia; with carbon, the poisonous one,
cyanogen, the base of prussic acid; with chlorine it gives rise to a
fluid, oily in its appearance, but which, when merely touched by an
unctuous body, explodes more violently than any other known compound,
shivering whatever vessel it may be contained in, to atoms; with iodine
it is only slightly less violent; and in certain combinations with
silver, mercury, gold, or platinum, it produces fulminating compounds
of the most dangerous character.[201] Here we have elements harmless
when uncombined, exhibiting the most destructive effects if their
combinations are at all disturbed; and in the other case we have inert
masses produced from active and injurious agents.

We regard a certain number of substances as _elementary_; that is to
say, not being able, in the present state of our knowledge, to reduce
them to any more simple condition, they are considered as the elements
which by combination produce the variety of substances found in the
three kingdoms of nature.

We have already spoken of the atomic constitution of bodies. It remains
now to explain the simplicity and beauty which mark every variety of
combination under chemical force. As a prominent and striking example,
water is a compound of two gaseous bodies, oxygen and hydrogen:--

If we decompose water by means of galvanic electricity, or determine
its composition by direct chemical analysis, we shall find it consists
of two volumes of hydrogen gas, united to one volume of oxygen, or, by
weight, of one part of hydrogen combined with eight of oxygen. In 100
parts, therefore, we should find--

    Oxygen        88·9
    Hydrogen      11·0

It is found in the same way that the theoretical weight of the atom
of carbon is 6, and that of nitrogen 14; whilst the atom of iron is
28, that of silver 108, of gold 199, and that of platinum and iridium
each 98.[202] Now, as these are the relative weights of the ultimate
indivisible atom, it follows that all combinations must be either atom
to atom, or one to two, three, or four; but that in no case should
combination take place in any other than a multiple proportion of the
equivalent or atomic number. This is found to be the case. Oxygen,
for instance, combines as one, two, or three atoms; its combination
presenting some multiple of its equivalent number 8, as 16, or 24:
and in like manner the combining quantity of carbon is 6, or some
multiple of that number. Where this law is not found strictly to agree
with analytical results, of which some examples are afforded by the
sesquioxides, it may be attributed, without doubt, to some error of
analysis or in the method of calculation.

Nothing can be more perfect than the manner in which nature regulates
the order of combination. We have no uncertain arrangement; but,
however great the number of the atoms of one element may be, over those
of another, those only combine which are required, according to this
great natural law, to form the compound, all the others still remaining
free and uncombined. These results certainly appear to prove that the
elementary particles of matter are not of the same specific gravities.
Do they not also indicate that any alteration in the specific gravity
of the atom would give rise to a new series of compounds, thus
apparently producing a new element? Surely there is nothing irrational
in the idea that the influences of heat or electricity, or of other
powers of which as yet we know nothing, may be sufficient to effect
such changes in the atomic constituents of this earth.

The combination of elementary atoms takes place under the influence
of an unknown force which we are compelled to express by a figurative
term, _affinity_. In some cases it would appear that the disposition
of two bodies to unite, is determined by the electrical condition; but
a closer examination of the question than it is possible to enter into
in this place, clearly shows that some physical state, not electrical,
influences combining power.

Chemical affinity or attraction is the peculiar disposition which one
body has to unite with another. To give some instances in illustration.
Water and spirit combine most readily: they have a strong affinity for
each other. Water and oil repel each other: they have no affinity;
they will not enter into combination. If carbonate of potash is added
to the spirit and water in sufficient quantity, the water is entirely
separated, and the pure spirit will float over the hydrated potash. If
potash is added to the oil and water, it combines with the oil, and,
forming soap, they all unite together; but, if we now add a little acid
to the mixture, the potash will quit the oil to combine with the acid,
and the oil will be repelled as before and float on the liquid. This
has been called single elective affinity. These elections were regarded
as constant, and chemists drew up tables for the purpose of showing the
order in which these decompositions occur.[203] Thus, ammonia, it was
shown, would separate sulphuric acid from magnesia, lime remove it from
ammonia, potash or soda from lime, and barytes from potash or soda. It
was thought the inverse of this order would not take place, but recent
researches have shown that the results are modified by quantity and
some other conditions.

It often happens that we have a compound action of this kind in which
double election is indicated. Sulphate of lime and carbonate of ammonia
in solution are brought together, and there result a carbonate of lime
and a sulphate of ammonia. Now, in such cases nothing more than single
elective attraction most probably occurs, and the carbonic acid is
seized by the lime, by the great affinity of that earth for carbonic
acid, only after it has been set free from the ammonia, and then, by
the force of cohesion acting with the combining powers, the insoluble
salt is precipitated.[204] There is a curious fact in connection with
this decomposition. If carbonate of lime and sulphate of ammonia
are mixed together dry, and exposed, in a closed vessel, to a red
heat, sulphate of lime and carbonate of ammonia are formed. These
opposite effects are not very easily explained. The action of heat is
to set free the carbonic acid; and it can only be by supposing that
considerable differences of temperature reverse the laws of affinity,
that we can at all understand this phenomenon. That different effects
result at high temperatures from those which prevail at low ones,
recent experiments prove to us, particularly those of Boutigny, already
quoted when considering decomposition by calorific action.

Under the term chemical affinity, which we regard as a power acting
at insensible distances, and producing a change in bodies, we are
content to allow ourselves to believe that we have explained the
great operations of nature. We find that the vegetable and animal
kingdoms are composed of carbon, hydrogen, oxygen, and nitrogen. The
granite mountains of the earth, and its limestone hills, and all its
other geological formations, are found to be metals and oxygen, and
carbon and sulphur, disposed to settle in harmonious union in their
proper places by chemical affinity. But what really is the power which
combines atom to atom, and unites molecule to molecule? Can we refer
the process to heat? The influence of caloric, although by changing
the form of bodies it sometimes assists combination, is to be regarded
rather as in antagonism to the power of cohesion. Can it be thought
that electricity is active in producing the result? During every change
of state, those phenomena which we term electrical are manifested; but
we thereby only prove the general diffusion of the electric principle,
and by no means show that electricity is the cause of the chemical
change. Can light determine these changes? It is evident, although
light may be a disturbing power, that it cannot be the effective one;
for many of these decompositions and recompositions are constantly
going on within the dark and silent depths of the earth, to which a
sunbeam cannot reach. That the excitation on the surface of the earth,
produced by solar influence, may modify those changes, is probable. It
is, however, certain that we must regard all manifestations of chemical
force as dependent upon some secret principles common to all matter,
diffused throughout the universe, but modified by the influences of the
known imponderable elements, and by the mechanical force of aggregative
attraction.

Bodies undergo remarkable changes of form, and present very different
characters, by reactions, which are of several kinds. We suppose
that a permanent corpuscular arrangement is maintained so long as
the equilibrium of the molecular forces is undisturbed. Water, for
instance, remains unchanged so long as the balance of affinity is kept
up between the oxygen and hydrogen of which it is composed, or so long
as the oscillations of force between these combining elements are
equal; but disturb this force, or set up a new vibratory action, as by
passing an electric current through the water, or by presenting another
body, which has the power of reacting upon one of these corpuscular
systems, and the water is decomposed, the hydrogen and oxygen gases
being set free, or one alone is liberated, and the other combined with
the molecules of the agent employed, and a new compound produced. This
is chemistry, by which science we discover all the combinations of
matter.

Having reason to conclude that atom combines with atom, according to
a system most harmoniously arranged, there can be no difficulty in
conceiving that molecule unites with molecule, in a manner regulated
by some equally well-marked law. It was, indeed, a discovery by
Wenzel, of Fribourg, that, in salts which decompose each other, the
acid which saturates one base will also saturate the other base;
and the subsequent observations of Richter, of Berlin, who attached
proportional numbers to the acids and bases, and who remarked that the
neutrality of metallic salts does not change during the precipitation
of metals by each other, which led the way to the atomic theory of Dr.
Dalton, to whom entirely belongs the observation, that the equivalent
of a compound body is the sum of the equivalents of its constituents,
and the discovery of combination in multiple proportions.

The elements of a molecule can take a new arrangement amongst
themselves, without any alteration in the number of the atoms or of
their weight, and thus give rise to a body of a different form and
colour, although possessing the same chemical constitution. This is the
case with many of the organic compounds of carbon and hydrogen.

The elements of a compound may be disassociated, and thus the
dissimilar substances of which it is composed set free. A piece
of chalk exposed to heat is, by the disturbance of its molecular
arrangement, changed in its nature; a gaseous body, carbonic acid,
is liberated, and quick-lime (oxide of calcium) is left behind. If
this carbonic acid is passed through red-hot metal tubes, or brought
in contact with heated potassium, it is resolved into oxygen and
charcoal--the oxygen combining with the metal employed. The oxide of
calcium (lime), if subjected to the action of a powerful galvanic
current, is converted into oxygen and a metal, calcium. Thus we learn
that chalk is a body consisting of two compound molecules,--carbonic
acid, which is formed by the combination of an atom of carbon with two
atoms of oxygen,--and lime, which results from the union of an atom of
calcium with one of oxygen.

The condition requisite to the production of chemical action between
bodies is that they should be dissimilar. Two elementary atoms
are placed within the spheres of each other’s influences, and a
compound molecule results. Oxygen and hydrogen form water; oxygen
and carbon give rise to carbonic acid; nitrogen and hydrogen unite
to form ammonia; and chlorine and hydrogen to produce hydrochloric
acid. In all these cases an external force is required to bring the
atoms within the range of mutual affinity: flame,--the electrical
spark,--actinism,--or the interposition of a third body, is necessary
in each case. There are other examples in which no such influence is
required. Potassium and oxygen instantly unite: chlorine, iodine, and
bromine immediately, and with much violence, combine with the metals to
form chlorides, iodides, or bromides.

With compound molecules the action is in many cases equally active,
and combination is readily effected, as in the cases of the acids and
the oxides of some metals, which are all instances of the most common
chemical attraction.

An elementary or simple molecule and molecules of a compound and
different constitution are brought together, and a new compound
results from an interchange of their atoms, whilst an element is
liberated. These are essentially illustrations of analytical chemistry.
Sulphuretted hydrogen is mixed with chlorine; the chlorine combines
with the hydrogen, and sulphur is set free. Potassium is put into
water, and it combines with the oxygen of the water, whilst the
hydrogen is liberated.

Two compound molecules being brought together may decompose each other,
and form two new compounds by an interchange of their elements.

One element may be substituted for another under certain circumstances.
Gold may be replaced by mercury; copper will take the place of silver;
and iron will occasion the separation of copper from its solutions,
the iron itself being dissolved to supply its place; chlorine will
substitute hydrogen in the carburetted hydrogen gases; and many other
examples might be adduced.

Chemical phenomena very frequently become of a complex character;
and one, two, or three of these cases may be occurring at the same
time in the decomposition of one compound by another. Such are the
general features of chemical science. Many peculiarities and remarkable
phenomena connected with chemical investigations will be named, as
the examination of the elementary composition of matter is proceeded
with; but, although the philosophy of chemical action is of the highest
interest, it must not be allowed to detain us with its details, which
are, indeed, more in accordance with a treatise on the science than
one which professes to do no more than sketch out those prevailing
and striking features which, whilst they elucidate the great truths
of nature, are capable of being employed as suggestive examples of
the tendency of scientific investigation to enlarge the boundaries of
thought, and give a greater elevation to the mind, leading us from
the merely mechanical process of analysis up to the great synthetical
operations, by which all that is found upon the earth for its ornament,
or our necessities, is created.

Among the most remarkable phenomena within the range of physical
chemistry are those of _Catalysis_, or, as it has also been called, the
“_Action of presence_.”[205] There are a certain number of bodies known
to possess the power of resolving compounds into new forms, without
undergoing any change themselves. Kirchoff discovered that the presence
of an acid, at a certain temperature, converted starch into sugar and
gum, no combination with the acid taking place. Thenard found that
manganese, platinum, gold, and silver, and, indeed, almost any solid
organic body, had the power of decomposing the binoxide of hydrogen by
their presence merely, no action being detected on these bodies. Edmund
Davy found that powdered platinum, moistened with alcohol, became
red-hot, fired the spirit, and converted it into vinegar, without
undergoing, itself, any chemical change. Döbereiner next discovered
that spongy platinum fired a current of hydrogen gas directed upon
it, which, by combining with the oxygen of the air, formed water.
Dulong and Thenard traced the same property, differing only in degree,
through iridium, osmium, palladium, gold, silver, and even glass.
Further investigation has extended the number of instances; and it has
even been found that a polished plate of platinum has the power of
condensing hydrogen and oxygen so forcibly upon its surface, that these
gases are drawn into combination and form water, with a development of
heat sufficient to ignite the metal.

This power, whatever it may be, is common in both organic and inorganic
nature, and on its important purposes Berzelius has the following
remarks:--

“This power gives rise to numerous applications in organic nature;
thus, it is only around the eyes of the potato that diastase exists:
it is by means of catalytic power that diastase, and that starch,
which are insoluble, are converted into sugar and into gum, which,
being soluble, form the sap that rises in the germs of the potato.
This evident example of the action of catalytic power in an organic
secretion, is not, probably, the only one in the animal and vegetable
kingdom, and it may hereafter be discovered that it is by an action
analogous to that of catalytic power, that the secretion of such
different bodies is produced, all which are supplied by the same
matter, the sap in plants, and the blood in animals.”[206]

It is, without doubt, to this peculiar agency that we must attribute
the abnormal actions produced in the blood of living animals by the
addition of any gaseous miasma or putrid matter, of which we have, in
all probability, a fearful example in the progress of Asiatic cholera;
therefore the study of its phenomena becomes an important part of
public hygiène.

Physical research has proved to us that all bodies have peculiar
powers, by which they condense with varying degrees of force gases
and vapours upon their surfaces; every body in nature may, indeed, be
regarded as forming its own peculiar atmosphere. To this power, in all
probability, does catalysis belong. Different views have, however,
prevailed on this subject, and Dr. Lyon Playfair[207] argues that the
catalytic force is merely a modified form of chemical affinity, exerted
under peculiar conditions.

Whatever may be the power producing chemical change, it acts in
conformity with some fixed laws, and in all its transmutations, an
obedience to a most harmonious system is apparent.

It is curious to observe the remarkable character of many of these
natural transmutations of matter, but we must content ourselves with a
few examples only. For instance:--

Sugar, oxalic acid, and citric acid are very unlike each other, yet
they are composed of the same elements; the first is used as a general
condiment, the second is a destructive poison, and the third a grateful
and healthful acid: sugar is readily converted into oxalic acid, and
in the process of ripening fruits nature herself converts citric acid
into sugar. Again, starch, sugar, and gum would scarcely be regarded
as alike, yet their only difference is in the mode in which carbon,
hydrogen, and oxygen combine. They are composed of the same principles,
in the following proportions:--

              Carbon.  Hydrogen.  Oxygen.
    Starch      12        10        10
    Sugar       12        11        11
    Gum         12        11        11

These _isomeric_ groups certainly indicate some law of affinity which
science has not yet discovered. Similar and even more remarkable
instances might be adduced of the same elements producing compounds
very unlike each other; but the above have been selected from their
well-known characters. Indeed, we may state with truth that all the
varieties of the vegetable world--their woody fibre--their acid or
alkaline juices--the various exudations of plants--their flowers,
fruit, and seeds, and the numerous products which, by art, they are
made to yield for the uses of man, are, all of them, compounds of these
three elements, differing only in the proportions in which they are
combined with nitrogen, or in some peculiar change of state in one
or other of the elementary principles. The chemist is now enabled by
simple processes, from the refuse of manufactories to produce fruit
essences which are equal in flavour to the natural production; and from
benzoic acid, which is obtained in great abundance from the houses in
which cows are kept, the most delicate essences are produced, which
are given to the world as the distillations of a thousand flowers.
By the impulse given to organic chemistry by Liebig, our knowledge
of the almost infinite variety of substances, in physical character
exceedingly dissimilar, which result from the combination of oxygen,
hydrogen, and carbon, in varying proportions, has been largely
increased. And the science is now in that state which almost causes
a regret that any new organic compounds should be discovered, until
some industrious mind has undertaken the task of reducing to a good
general classification the immense mass of valuable matter which has
been accumulated, but which, for all practical purposes, remains nearly
useless and unintelligible.

These combinations, almost infinitely varied as they are, and so
readily produced and multiplied as to be nearly at the will of the
organic analyst, are not, any of them, accidental: they are the result
of certain laws, and atom has united with atom in direct obedience
to principles which have been through all time in active operation.
They are unknown; the researches of science have not yet developed
them, and the philosopher has not yet made his deductions. They are
to be referred to some secret fixed principles of action, to a force
which has impressed upon every atom of the universe its distinguishing
character. Chemistry makes us familiar with a system of order. The
researches of analysts have proved that every body has a particular
law of combination, to which it is bound by a mathematical precision;
but it is not proportional combination alone we have to consider. If
_allotrophy_ is evidenced in the mineral world, it is certainly far
more strikingly manifested in the vegetable and animal kingdoms.

There are some cases in which bodies appear to combine without any
limitation, as spirit of wine and water, sulphuric acid and water;
but these must be considered as conditions of mixture rather than of
chemical combination.

The composition of bodies is fixed and invariable, and a compound
substance, so long as it retains its characteristic properties, must
consist of the same elements united in the same proportions. Thus,
sulphuric acid is invariably composed of 16 parts of sulphur and 24
parts of oxygen. Chalk, whether formed by nature or by the chemist,
yields 43·71 parts of carbonic acid, and 56·29 parts of lime. The rust
which forms upon the surface of iron by the action of the atmosphere,
is as invariable in its composition as if it had been formed by the
most delicate adjustment of weight by the most accurate manipulator,
being 28 parts of iron and 12 parts of oxygen. This law is the basis of
all chemical inquiry, all analytical investigations depending upon the
knowledge it affords us, that we can only produce certain undeviating
compounds as the results of our decompositions. We are not in a
position to offer any explanation which will account for these constant
quantities in combination. The forces of cohesion and elasticity
have been advanced in explanation, on the strength of the fact that
the solubility of a salt in water is regulated by cohesion, and that
of a gas by its elasticity. Although it may appear that some cases
of chemical combination are due to these powers,--as, for instance,
when the union of oxalic acid or sulphuric acid with lime produces
an insoluble salt,--we cannot thus explain the constant proportions
in which the metals, sulphur, oxygen, and similar bodies, unite. It
is quite certain there is a power or principle, which we have not
yet reached, upon which are dependent all the phenomena which we now
embrace under the term chemical affinity.

Another law teaches us that when compound bodies combine in more than
one proportion, every additional union represents a multiple of the
combining proportion of the first. With the difficulty which arises
from the sub-multiple compounds we cannot deal:--further research may
render their laws less obscure. We have seen that 8 parts of oxygen
unite with 1 of hydrogen and 14 of nitrogen. It also unites with 110 of
silver, 96 of platinum, 40 of potassium, 36 of chlorine, and 200 parts
of mercury, giving rise to--

    Water                    9
    Nitrous oxide           22
    Oxide of silver        118
    Oxide of platinum      104
    Potash                  48
    Oxide of chlorine       44
    Oxide of mercury       208

In these proportions, or in multiples of them, and in no others, will
these bodies unite with the acids or other compounds. It will, of
course, be understood that any other numbers may be adopted, provided
they stand in the same relation to each other.[208]

From the discovery of these harmonious arrangements was deduced the
beautiful atomic theory to which allusion has been already made.
Indeed, there does not appear to be any other way of explaining these
phenomena than by the hypothesis that the ultimate atoms of bodies have
_relatively_ the weights which we arbitrarily assign to them, as their
combining quantities. These views are further confirmed by the fact,
that gaseous bodies unite together by volume in very simple definite
proportions:--100 measures of hydrogen and 200 measures of oxygen form
water; 100 measures of oxygen and 100 measures of vapour of sulphur
form sulphurous acid gas. Ammoniacal gas consists of 300 volumes of
hydrogen and 100 volumes of nitrogen, condensed by combination into 200
volumes; consequently, we are enabled most readily to calculate the
specific gravity of ammoniacal gas. The specific gravity of nitrogen
is 0·9722, that of hydrogen 0·0694. Now, three volumes of hydrogen are
equal to 0·2082: this added to 0·9722 is equal to 1·1804, which is
exactly the specific gravity obtained by experiment.

There is no doubt, from the generality with which this law of volumes
prevails, that it would be found to extend through all substances,
provided they could be rendered gaseous; in other words, there is
abundant proof to convince us that throughout nature the process of
combination, in the most simple ratio of volumes, is in operation to
produce all the forms of matter known to us.

It has been shown, by the investigations of Dr. Dalton, in 1840, that
salts, containing water of crystallization, dissolve in water without
increasing the bulk of the fluid more than is due to the liquefaction
of the water which these salts contain; while Joule and Playfair
have shown that the anhydrous salts take up no space in solution.
From this we are naturally led to conclude that the volume occupied
by a salt in the solid state has a certain relation to the volume of
the same salt when in solution, and has also a fixed relation to the
volume occupied by any other salt. The law appears to be:--the atomic
volume of any salt whatever (anhydrous or hydrated) is a multiple of
11, or of a number near 11, or a multiple of 9·8 (the atomic volume
of ice), or the sum of a multiple of 11 or 9·8. Marignac, who has
also paid much attention to the subject, does not think these numbers
absolutely correct, but approximately so.[209] It would be a beautiful
exemplification of the simplicity of Nature’s operations, if it should
be clearly proved that the atomic volume of solid water (ice) regulated
the combining proportions by volume of all other bodies,--that it was
the standard by which chemical combination and ordinary solution were
determined.

In addition to the laws already indicated, there appear to be some
others of which, as yet, we have a less satisfactory knowledge, and,
as a remarkable case, we may adduce the phenomena of _substitution_,
or that power which an elementary body, under certain conditions,
possesses, of turning out one of the elements of a compound, and of
taking its place.[210] Thus, the hydrogen of a compound radical, as
carburetted hydrogen, may be replaced by chlorine, equivalent for
equivalent, and form a chloride of carbon, which being constructed
on the same type as the original, will have the same general laws of
combination.

Under the influence of these laws, all the combinations which we
discover in nature take place. The metals, and oxygen, and sulphur,
and phosphorus unite. The elements of the organic type, entering into
the closest relations, give rise to every form of vegetable life. The
acids, the gums, the resins, and the sugar which plants produce; and
those yet more complicated animal substances, bone, muscle, blood, and
bile; albumen, casein, milk, with those compounds which, under the
influence of vital power, resolve themselves into substances which are
essential to the existence, health, and beauty of the animal fabric,
are all dependent on these laws. But these metamorphoses must be
further considered in our examination of the more striking cases of
chemical action. The changes which result from organic combination are
so remarkable, and withal they show how completely the whole of the
material world is in subjection to chemical force, and every variety
of form the result of mysterious combination, that some particular
reference to these metamorphoses is demanded.

In nearly all cases of decided chemical action, all trace of the
characters of the combining bodies disappear. We say decided chemical
action, because, although sulphuric acid and water combine, and
salts dissolve in water, we may always recognize their presence, and
therefore these and similar cases cannot be regarded as strict examples
of the phenomena under consideration.

Hydrogen and oxygen, in combining, lose their gaseous forms, and are
condensed into a liquid--water. Sulphuric acid is intensely sour and
corrosive; potash is highly caustic; but united they form a salt
which is neither: they appear to have destroyed the distinguishing
characters of each other. Combined bodies frequently occupy less space
than they did previously to combination, of which numerous particular
instances might be adduced. Gases in many cases undergo a remarkable
condensation when chemically combined. In slaking lime, the water
becomes solid in the molecules of the hydrate of lime formed, and the
intense heat produced arises from the liberation of that caloric which
had been employed to keep the water liquid. When a solid passes into
the liquid state, cold is produced by the abstraction from surrounding
objects of the heat required to effect fluidity. An alteration of
temperature occurs whenever chemical change takes place, as we have
already shown, with a few trivial and uncertain exceptions. The
disturbance caused by the exercise of the force of affinity frequently
leads to the development of several physical powers.

Changes of colour commonly arise; indeed, there does not appear to be
any relation between the colour of a compound and that of its elements.
Iodine is of a deep iron-grey colour; its vapour is violet; yet it
forms beautifully white salts with the alkalies, a splendid red salt
with mercury, and a yellow one with lead. The salts of iron vary from
white and yellow to green and dark brown. Those of copper, a red metal,
are of a beautiful blue and green colour, and the anhydrous sulphate is
white.

Isomorphism, which appears in a very remarkable manner among the
organic compounds, has, under the head of crystallization, already had
our attention. There is also a class of bodies which are said to be
_isomeric_; that is, to have the same composition, although different
in their physical characters. But the idea that bodies exist, which,
although of a decidedly different external character, are of exactly
the same chemical composition and physical condition, is not tenable;
and in nearly all the examples which have been carefully examined, a
difference in the aggregate number of atoms, or in the mode in which
those atoms have respectively arranged themselves, or that peculiar
physical difference designated by the term _allotropy_, has been
detected.

Oil of turpentine and oil of lemons have the same composition, each
being composed of five equivalents of carbon and four of hydrogen.
These substances form, from the striking difference perceptible in
their external characters, a good example of isomerism.

The laws of organic chemistry are not, however, the same as those
applying to inorganic combinations. Organic chemistry is well defined
by Liebig, as the chemistry of compound radicals; and under the
influence of vitality, nature produces compounds which have all the
properties of simple elements.[211]

When we reflect upon the conditions which prevail throughout nature,
with a few of which only has science made us acquainted, we cannot fail
to be struck with the various phases of being which are presented to
our observation, and the harmonious system upon which they all appear
to depend.

When we discover that bodies are formed of certain determinate atoms,
which unite one with another, according to an arithmetical system, to
form molecules, which, combining with molecules, observe a similar law,
we see at once that all the harmonies of chemical combination--the
definite proportions, laws of volume, and the like--are but the
necessary consequences of these simple and guiding first principles.
In the pursuit of truth, investigators must discover still further
arrangements, which, from their perfection, may be compared to the
melodious interblending of sweet sounds, and many of the apparently
indeterminate combinations will, beyond a doubt, be shown to be as
definite as any others. But we cannot reflect upon the fact that these
atoms and these molecules are guided in their combinations by impulses,
which we can only explain by reference to human passions, as the term
_elective affinity_ implies, without feeling that an impenetrable
mystery of a grand and startling character in its manifestations
surrounds each grain of dust which is hurried along upon the wind.

We now, habitually, speak of attraction and repulsion--of the affinity
and non-affinity of bodies. We are disposed, from the discovery of the
attractive and repelling poles of electrified substances, to regard
these powers in all cases as depending upon some electrical state, and
we write learnedly upon the laws of these forces. After all, it would
be more honest to admit, that we know no more of the secret impulses
which regulate the combinations of matter, than did those who satisfied
themselves by referring all phenomena of these kinds to sympathies
and antipathies: terms which have a poetic meaning, conveying to the
mind, with considerable distinctness, the fact, and giving the idea
of a feeling--a passion--involving and directing inanimate matter,
similar to that which stirs the human heart, and certainly calculated
to convey the impression that there is working within all things a
living principle, and pointing, indeed, to “the soul of the world.” The
animated marble of ancient story is far less wonderful than the fact,
proved by investigation, that every atom of matter is penetrated by a
principle which directs its movements and orders its positions, and
involved by an influence which extends, without limits, to all other
atoms, and which determines their union, or otherwise.

We have gravitation, drawing all matter to a common centre, and
acting from all bodies throughout the wide regions of unmeasured
space upon all. We have cohesion, holding the particles of matter
enchained, operating only at distances too minute for the mathematician
to measure; and we have chemical attraction, different from either
of these, working no less mysteriously within absolutely insensible
distances, and, by the exercise of its occult power, giving determinate
and fixed forms to every kind of material creation.

The spiritual beings, which the poet of untutored nature gave to the
forest, to the valley, and to the mountain, to the lake, to the river,
and to the ocean, working within their secret offices, and moulding
for man the beautiful or the sublime, are but the weak creations
of a finite mind, although they have for us a charm which all men
unconsciously obey, even when they refuse to confess it. They are like
the result of the labours of the statuary, who, in his high dreams of
love and sublimated beauty, creates from the marble block a figure
of the most exquisite moulding which mimics life. It charms us for a
season; we gaze and gaze again, and its first charms vanish; it is ever
and ever still the same dead heap of chiselled stone. It has not the
power of presenting to our wearying eyes the change which life alone
enables matter to give; and we admit the excellence of the artist, but
we cease to feel at his work. The creations of poetry are pleasing, but
they never affect the mind in the way in which the poetic realities
of nature do. The sylph moistening a lily is a sweet dream; but the
thoughts which rise when first we learn that its broad and beautiful
dark-green leaves, and its pure and delicate flower, are the results
of the alchemy which changes gross particles of matter into symmetric
forms,--of a power which is unceasingly at work under the guidance of
light, heat, and electrical force,--are, after our incredulity has
passed away--for it is too wonderful for the untutored to believe at
once--of an exalting character.

The flower has grown under the impulse of principles which have
traversed to it on the solar beam, and mingled with its substance. A
stone is merely a stone to most men. But within the interstices of
the stone, and involving it like an atmosphere, are great and mighty
influences, powers which are fearful in their grander operations, and
wonderful in their gentler developments. The stone and the flower hold,
locked up in their recesses, the three great known forces--light, heat,
and electricity: and, in all probability, others of a more exalted
nature still, to which these powers are but subordinate agents. Such
are the facts of science, which, indeed, are the true “sermons in
stones,” and the most musical of “tongues in trees.” How weak are the
creations of romance, when viewed beside the discoveries of science!
One affords matter for meditation, and gives rise to thoughts of a most
ennobling character; the other excites for a moment, and leaves the
mind vacant or diseased. The former, like the atmosphere, furnishes
a constant supply of the most healthful matter; the latter gives
an unnatural stimulus, which compels a renewal of the same kind of
excitement, to maintain the continuation of its pleasurable sensations.


FOOTNOTES:

[200] All the phenomena connected with volcanic action, and the
theories connected therewith, will be found in Dr. Daubeny’s work, _A
description of active and extinct Volcanoes, of Earthquakes, and of
Thermal Springs_. 1848.

[201] Graham’s _Elements of Chemistry_. New Edition.

[202] Graham’s _Elements of Chemistry_; and Brande’s _Manual_.

[203] Of these _tables of attraction_ the following may be taken as a
specimen:--

    SULPHURIC ACID.
    Baryta.
    Strontia.
    Potassa.
    Soda.
    Lime.
    Magnesia.
    Ammonia.

It thus appears that baryta separates sulphuric acid from its compounds
with all inferior substances, and that ammonia is separated from the
acid by all that are above it.

[204] Berthollet: _Essai de Statique Chimique_, 1803. Sir Humphry Davy,
in his _Elements of Chemical Philosophy_, has given an excellent review
of the views of Berthollet.

[205] _On certain combinations of a new acid, formed of Azote, Sulphur,
and Oxygen_; by J. Pelouze. Translated from Annales de Chimie, vol.
xvi., for Scientific Memoirs, vol. i. p. 470. _Some ideas of a new
force acting in the combinations of Organic Compounds_, by Berzelius:
Annales de Chimie, vol. lxi. The conclusion come to by this eminent
chemist is expressed in the following translation:--“This new power,
hitherto unknown, is common both in organic and inorganic nature.
I do not believe that it is a power which is entirely independent
of the electro-chemical affinities of the substance. I believe, on
the contrary, that it is merely a new form of it; but so long as we
do not see their connection and mutual dependence, it will be more
convenient to describe it by a separate name. I shall, therefore, call
it _catalytic power_: I shall also call _catalysis_, the decomposition
of bodies by this force--in the same way as the decomposition of bodies
by chemical affinity is termed analysis.”

[206] Berzelius: _Annales de Chimie_, vol. lxi.

[207] _On Transformations produced by Catalytic Bodies_: by Lyon
Playfair, Esq.; Phil. Mag., vol. xxxi. p. 191, 1847.--“Facts have been
brought forward to show that there is at least as much probability in
the view that the catalytic force is merely a modified form of chemical
affinity exerted under peculiar conditions, as there is in ascribing
it to an unknown power, or to the communication of an intestine motion
to the atoms of a complex molecule. Numerous cases have been cited,
in which the action results when the assisting or catalytic body is
not in a state of change; and attempts have been made to prove, by new
experiments, that the catalytic power exercises its peculiar power by
acting in the same direction as the body decomposing, or entering into
union, but under conditions in which its own affinity cannot always be
gratified.”

[208] Consult Graham’s Chemistry, _On Combining Proportions_.

[209] _Memoir on Atomic Volume and Specific Gravity._ Messrs. Lyon
Playfair and Joule.--Philosophical Magazine, vol. xxvii. p. 453, or
Transactions of Chemical Society of London. _Observations_ on the
above, by Professor de Marignac.--Bibliothèque Universelle, Feb. 1846.
_On the Relation of the Volumes of bodies in the solid state, to their
equivalents, or atomic weights_: by Professor Otto. _Studies on the
connection between the atomic weights, crystalline form, and density
of bodies_: by M. Filhol. Translated for the Cavendish Society, and
published in their Chemical Reports and Memoirs.

[210] _Comptes Rendus de l’Académie des Sciences_, 1840, No. 5. A good
translation of Dumas’s Memoir appeared in the Philosophical Magazine,
from which I extract the following familiar exposition of the laws of
substitution:--“Let me make a comparison drawn from a familiar order of
ideas. Let us put ourselves in the place of a man overlooking a game at
chess without the slightest knowledge of the game. He would soon remark
that the pieces must be used according to positive rules. In chemistry,
the equivalents are our pieces, and the law of substitutions one of the
rules which preside over their moves. And as in the oblique move of the
pawns one pawn must be substituted for another, so in the phenomena
of substitution one element must take the place of another. But this
does not hinder the pawn from advancing without taking anything, as the
law of substitution does not hinder an element from acting on a body
without displacing or taking the place of any other element that it may
contain.”--_Memoir on the Law of Substitutions, and Theory of Chemical
Types._

[211] Liebig’s _Chemistry in its application to Agriculture and
Physiology_: translated by Lyon Playfair, Ph. D. _Animal Chemistry, or
Chemistry in its application to Physiology and Pathology_: by Justus
Liebig; translated by Wm. Gregory.




CHAPTER XII.

CHEMICAL PHENOMENA.

  Water--Its Constituents--Oxygen--Hydrogen--Peroxide
    of Hydrogen--Physical Property of Water--Ice--Sea
    Water--Chlorine--Muriatic Acid--Iodine--Bromine--Compounds
    of Hydrogen with Carbon--Combustion--Flame--Safety
    Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic
    Acid--Influence of Plants on the Air--Chemical Phenomena of
    Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c. &c.


Without attempting anything which shall approach even to the character
of a sketch of chemical science, we may be allowed, in our search
after exalting truths, to select such examples of the results of
combination as may serve to elucidate any of the facts connected with
natural phenomena. In doing this, by associating our examination with
well-known natural objects or conditions, the interpretation afforded
by analysis will be more evident, and the operation of the creative
forces rendered more striking and familiar, particularly if at the same
time we examine such physical conditions as are allied in action, and
are sufficiently explanatory of important features.

A large portion of this planet is covered by the waters of the ocean,
of lakes and rivers. Water forms the best means of communication
between remote parts of the earth. It is in every respect of the
utmost importance to the animal and vegetable kingdom; and, indeed, it
is indispensable in all the great phenomena of the inorganic world.
The peculiarities of saltness or freshness in water are dependent
upon its solvent powers. The waters of the ocean are saline from
holding dissolved various saline compounds, which are received in
part from, and imparted also to, the marine plants. Perfectly pure
water is without taste: even the pleasant character of freshly-drawn
spring-water is due to the admixture of atmospheric air and carbonic
acid. The manner in which water absorbs air is evidently due to a
peculiar physical attractive force, the value of which we do not at
present clearly perceive or correctly estimate. It is chemically
composed of two volumes of hydrogen gas--the lightest body known, and
at the same time a highly inflammable one--united with one volume of
oxygen, which excites combustion, and continues that action,--producing
heat and light,--with great energy. By weight, one part of hydrogen
is united with eight of oxygen, or in 100 parts of water we find 88·9
oxygen, and 11·1 of hydrogen gas. That two such bodies should unite to
furnish the most refreshing beverage, and indeed the only natural drink
for man and animals, is one of the extraordinary facts of science.
Hydrogen will not support life--we cannot breathe it and live; and
oxygen would over-stimulate the organic system, and, producing a kind
of combustion, give rise to fever in the animal frame; but, united,
they form that drink, for a drop of which the fevered monarch would
yield his diadem, and the deprivation of which is one of the most
horrid calamities that can be inflicted upon any living thing. Water
appears as the antagonist principle to fire, and the ravages of the
latter are quenched by the assuaging powers of the former; yet a
mixture of oxygen and hydrogen gases, in the exact proportion in which
they form water, explodes with the utmost violence on the contact of
flame, and, when judiciously arranged, produces the most intense degree
of heat known;--such is the remarkable difference between a merely
mechanical mixture and a chemical combination. Beyond this, we have
already noticed the remarkable fact that water deprived of air is
explosive at a comparatively low temperature, less than 300°; gunpowder
requiring a temperature of nearly 1000° F.

If we place in a globe, oxygen and hydrogen gases, in the exact
proportions in which they combine to form water, they remain without
change of state. They appear to mix intimately; and, notwithstanding
the difference in the specific gravities of the two gases, the lighter
one is diffused through the heavier in a curious manner, agreeably to
a law which has an important bearing on the conditions of atmospheric
phenomena.[212] The moment, however, that an incandescent body, or
the spark from an electric machine, is brought into contact with the
mixed gases, they ignite, explode violently, and combine to form water.
The discovery of the composition of water was thus synthetically made
by Cavendish--its constitution having been previously theoretically
announced by Watt.[213]

If, instead of combining oxygen and hydrogen in the proportions in
which they form water, we compel the hydrogen to combine with an
additional equivalent of oxygen, we have a compound possessing many
properties strikingly different from water. This--peroxide of hydrogen,
as it is called--is a colourless liquid, less volatile than water,
having a metallic taste. It is decomposed at a low temperature, and,
at the boiling point, the oxygen escapes from it with such violence,
that something like an explosion ensues. All metals, except iron, tin,
antimony, and tellurium, have a tendency to decompose this compound,
and separate it into oxygen and water. Some metals are oxidized during
the decomposition, but gold, silver, platinum, and a few others,
still retain their metallic state. If either silver, lead, mercury,
gold, platinum, manganese, or cobalt, in their highest states of
oxidation, are put into a tube, containing this peroxide of hydrogen,
its oxygen is liberated with the rapidity of an explosion, and so
much heat is excited that the tube becomes red hot. These phenomena,
to which we have already referred in noticing catalysis, are by no
means satisfactorily explained, and the peculiar bleaching property
possessed by the peroxide of hydrogen sufficiently distinguishes it
from water. There are few combinations which show more strikingly than
this the difference arising from the chemical union of an additional
atom of one element. Similar instances are numerous in the range
of chemical science; but scarcely any two exhibit such dissimilar
properties. During the ordinary processes of combustion, it has been
long known that water is formed by the combination of the hydrogen of
the burning body with the oxygen of the air. The recent researches of
Schönbein have shown that a peculiar body, which has been regarded as
a peroxide of hydrogen, to which he has given the name of OZONE, is
produced at the same time, and that it is developed in a great many
ways, particularly during electrical changes of the atmosphere. Thus
we obtain evidence that this remarkable compound, which was considered
as a chemical curiosity merely, is diffused very generally through
nature, and produced under a great variety of circumstances. During
the excitation of an electrical machine, or the passage of a galvanic
current through water by the oxidation of phosphorus, and probably
in many similar processes--in particular those of combustion, and we
may therefore infer also of respiration--this body is formed. From
observations which have been made, it would appear that, during the
night, when the activity of plants is not excited by light, they act
upon the atmosphere in such a way as to produce this ozone; and its
presence is said to be indicated by its peculiar odour during the
early hours of morning. We are not yet acquainted with this body
sufficiently to speculate on its uses in nature: without doubt, they
are important, perhaps second to those of water only. It is probable,
as we have already had occasion to remark, that ozone may be the active
agent in removing from the atmosphere those organic poisons to which
many forms of pestilence are traceable; and it is a curious fact, that
a low electrical intensity, and a consequent deficiency of atmospheric
ozone, marks the prevalence of cholera, and an excess distinguishes the
reign of influenza.[214]

Some interesting researches appear to show the probability that ozone
is simply oxygen in a state of high activity. It has been found,
indeed, that perfectly dry oxygen, which will not bleach vegetable
colours in the dark, acquires, by exposure to sunshine, the power of
destroying them. Becquerel has proved that this ozonous state may be
produced in dry oxygen by passing a succession of electric sparks
through it. Fremy passed the electric sparks on the outside of a tube
which contained perfectly dry oxygen, and it was found to have acquired
the properties of ozone. In this case, and probably in the experiments
of Becquerel, the light of the spark, rather than the electricity,
appears to have been the active agent in producing this change.
Schönbein himself does not appear disposed to regard ozone as being
either peroxide of hydrogen, or an allotropic oxygen. He leans to his
first view of its being an entirely new chemical element. The energy
of this ozone is so great, that it has been found to destroy almost
instantaneously the Indian-rubber union joints of the apparatus in
which it is formed.[215]

Water, from the consideration of which a digression has been indulged
in, to consider the curious character of one of its elements,--water is
one of the most powerful chemical agents, having a most extensive range
of affinities, entering directly into the composition of a great many
crystallizable bodies and organic compounds. In those cases where it is
not combined as water, its elements often exist in the proportions in
which water is formed. Gum, starch, and sugar, only differ from each
other in the proportions in which the elements of water are combined
with the carbon.

In saline combinations, and also in many organic forms, we must regard
the water as condensed to the solid form; that is, to exist as ice. We
well know that, by the abstraction of heat, this condition is produced;
but, in chemical combinations, this change must be the result of the
mechanical force exerted by the power of the agency directing affinity.

In the case of water passing from a liquid to a solid state, we have a
most beautiful exemplification of the perfection of natural operations.
Water conducts heat downwards but very slowly; a mass of ice will
remain undissolved but a few inches under water, on the surface of
which, ether, or any other inflammable body, is burning. If ice (solid
water) swam beneath the surface, the summer sun would scarcely have
power to thaw it; and thus our lakes and seas would be gradually
converted into solid masses at our ordinary winter temperatures.

All similar bodies contract equally during the process of cooling,
from the highest to the lowest points to which the experiments have
been carried. It has been thought that if this applied to water,
the result would be the sudden consolidation of the whole mass. A
modification of the law has been supposed to take place to suit the
peculiar circumstances of water. Nature never modifies a law for a
particular purpose; we must, therefore, seek to explain the action of
the formation of ice, as we know it, by some more rational view.

Water expands by heat, and contracts by cold; consequently, the
coldest portions of this body occupy the lower portions of the fluid;
but it must be remembered that these parts are warmed by the earth.
Ross, however, states that at the depth of 1,000 fathoms the sea
has a constant temperature of 39°. Water is said to be at its point
of greatest density at 40° of Fahrenheit’s thermometer; in cooling
further, this fluid appears to expand, in the same way as if heated:
and, consequently, water colder than this point, instead of being
heavier, is lighter, and floats on the surface of the warmer fluid.
It does not seem that any modification of the law is required to
account for this phenomenon. Water cooled to 40° still retains its
peculiar corpuscular arrangement; but immediately it passes below that
temperature, it begins to dispose itself in such a manner that visible
crystals may form the moment it reaches 32°. Now, if we conceive
the particles of water, at 39°, to arrange themselves in the manner
necessary for the assumption of the solid form, by the particular
grouping of molecules in an angular instead of a spheroidal shape,
it will be clear, from what we know of the arrangement of crystals
of water--ice--that they must occupy a larger space than when the
particles are disposed, side by side, in minute spheres. Even the
escape of air from the water in which it is dissolved is sufficient to
give an apparent lightness to the colder water. This expansion still
goes on increasing, from the same cause, during the formation of ice,
so that the specific gravity of a mass of frozen water is less than
that of water at any temperature below 40°. It must not be forgotten
that ice always contains a large quantity of air, by which it is
rendered buoyant.

Water, at rest, may be cooled many degrees below the freezing point
without becoming solid. This is easily effected in a thin glass flask;
but the moment it is agitated, it becomes a firm mass. Here we have the
indication of another cause aiding in producing crystals of ice on the
surface of water, under the influence of the disturbance produced by
the wind, which does not extend to any depth.

As oxygen and hydrogen gases enter largely into other chemical
compounds besides water, it is important to consider some of the forms
of matter into the composition of which these elements enter. To
examine this thoroughly, a complete essay on chemical philosophy would
be necessary; we must, therefore, be content with referring to a few of
the more remarkable instances.

The waters of the ocean are salt: this arises from their holding, in
solution chloride of sodium (_muriate of soda_--_common culinary salt_)
and other saline bodies. Water being present, this becomes muriate of
soda,--that is, a compound of muriatic acid and soda: muriatic acid
is hydrogen, combined with a most remarkable gaseous body, called,
from its yellow colour, _chlorine_; and soda, oxygen in union with
the metal sodium,--therefore, when anhydrous, culinary salt is truly
a chloride of sodium. Chlorine in some respects resembles oxygen; it
attacks metallic bodies with great energy; and, in many cases, produces
the most vivid incandescence, during the process of combination. It
is a powerful bleaching agent, is destructive to animal life, and
rapidly changes all organic tissues. There are two other bodies in
many respects so similar to chlorine, although one is at the ordinary
temperatures solid, and the other fluid, and which are also discovered
in sea-water, or in the plants growing in it, that it is difficult to
consider them otherwise than as different forms of the same principle.
These are iodine and bromine, and they both unite with hydrogen to
form acids. The part which chlorine performs in nature is a great and
important one. Combined in muriate of soda, we may trace it in large
quantities through the three kingdoms of nature, and the universal
employment of salt as a condiment indicates the importance to the
animal economy of the elements composing it. Iodine has been traced
through the greater number of marine plants, existing, apparently as
an essential element of their constitution; in some land plants it has
also been found, particularly in the Armeria maritima, when this plant
grows near the sea:[216] it has been detected in some mineral springs,
and in small quantities in the mineral kingdom[217] combined as iodide
of silver, and in the aluminous slate of Latorp in Sweden.[218] Bromine
is found in sea-water, although in extremely minute quantities, in a
few saline springs, and in combination with silver; but we have no
evidence to show that its uses are important in nature.

Hydrogen, again, unites with carbon in various proportions, producing
the most dissimilar compounds. The air evolved from stagnant water,
and the fire-damp of the coal mine, are both carburetted hydrogen; and
the gas which we employ so advantageously for illumination, is the
same, holding an additional quantity of carbon in suspension. Naphtha,
and a long list of organic bodies, are composed of these two chemical
elements.

These combinations lead us, naturally, to the consideration of the
great chemical phenomena of combustion, which involve, indeed, the
influences of all the physical powers. By the application of heat,
we produce an intense action in a body said to be combustible; it
burns,--a chemical action of the most energetic character is in
progress, the elements which constitute the combustible body are
decomposed, they unite with some other elementary principles, and new
compounds are formed. A body burns--it is entirely dissipated, or it
leaves a very small quantity of ashes behind unconsumed, but nothing
is lost. Its volatile parts have entered into new arrangements, the
form of the body is changed, but its constituents are still playing an
important purpose in creation.

The ancient notion that fire was an empyreal element, and the Stahlian
hypothesis of a phlogistic principle on which all the effects of
combustion depended,[219] have both given way to the philosophy of the
unfortunate Lavoisier--which has, indeed, been modified in our own
times--who showed that combustion is but the development of heat and
light under the influence of chemical combination.

Combustion was, at one period, thought to be always due to the
combination of oxygen with the body burning, but research has shown
that vivid combustion may be produced where there is no oxygen. The
oxidizable metals burn most energetically in chlorine, and some of
them in the vapour of iodine and bromine, and many other unions take
place with manifestations of incandescence. Supporters of combustion
were, until lately, regarded as bodies distinct from those undergoing
combustion. For example, hydrogen was regarded as a combustible body,
and oxygen as a supporter of combustion. Such an arrangement is a
most illogical one, since we may _burn_ oxygen in an atmosphere of
hydrogen, in the same manner as we burn hydrogen in one of oxygen; and
so, in all the other cases, the supporter of combustion may be burnt
in an atmosphere formed of the, so called, combustible. The ordinary
phenomena of combustion are, however, due to the combination of oxygen
with the body burning; therefore every instance of oxidization may be
regarded as a condition of combustion, the difference being only one of
degree.

Common iron, exposed to air and moisture, _rusts_; it combines with
oxygen. Pure iron, in a state of fine division, unites with oxygen so
eagerly, that it becomes incandescent, and in both cases oxide of iron
is formed. This last instance is certainly a case of combustion; but
in what does it differ from the first one, except in the intensity of
the action? The cases of spontaneous combustion which are continually
occurring are examples of an analogous character to the above.
Oxygen is absorbed, it enters more or less quickly, according to
atmospheric conditions, into chemical combination; heat is evolved, and
eventually,--the action continually increasing,--true combustion takes
place. In this way our cotton-ships, storehouses of flax, piles of
oiled-cloth, sawdust, &c., frequently ignite; and to such an influence
is to be attributed the destruction of two of our ships of war, a few
years since, in Devonport naval arsenal.[220]

In the economic production of heat and light, we have the combination
of hydrogen and carbon with the oxygen of common air, forming water
and carbonic acid. In our domestic fires we employ coal, which is
essentially a compound of carbon and hydrogen containing a little
oxygen and some nitrogen, with some earthy matters which must be
regarded as impurities; the taper, whether of wax or tallow, is made up
of the same bodies, differing only in their combining proportions, and,
like coal gas, these burn as carburetted hydrogen. All these bodies
are very inflammable, having a tendency to combine energetically with
oxygen at a certain elevation of temperature.

We are at a loss to know how heat can cause the combination of those
bodies. Sir Humphry Davy has shown that hydrogen will not burn, nor
a mixture of it with oxygen explode, unless directly influenced by a
body heated so as to _emit light_.[221] May we not, therefore, conclude
that the chemical action exhibited in a burning body is a development
of some latent force, with which we are unacquainted, produced by the
absorption of light;--that a repulsive action at first takes place,
by which the hydrogen and carbon are separated from each other;--and
that in the nascent state they are seized by the oxygen, and again
compelled, though in the new forms of water and carbonic acid, to
resume their chains of combining affinity?

Every equivalent of carbon and of hydrogen in the burning body unites
with two equivalents of oxygen, in strict conformity with the laws
of combination. The flame of hydrogen, if pure, gives scarcely any
light, but combined with the solid particles of carbon, it increases
in brightness. The most brilliant of the illuminating gases is the
olefiant gas, produced by the decomposition of alcohol, and it is
only hydrogen charged with carbon to the point of saturation. Flame
is a cone of heated vapour, becoming incandescent at the points of
contact with the air; a mere superficial film only being luminous. It
is evident that all the particles of the gas are in a state of very
active repulsion over the surface, since flame will not pass through
wire gauze of moderate fineness. Upon this discovery is founded the
inimitable safety-lamp of Davy, by means of which the explosive gases
of a mine are harmlessly ignited within a cage of wire gauze. This
effect has been attributed to a cooling influence of the metal; but,
since the wires may be brought to a degree of heat but little below
redness without igniting the fire-damp, this does not appear to be the
cause. The conditions of the safety lamp may be regarded as presenting
examples exactly the converse of those already stated with reference to
the spheroidal state of water; and it affords additional evidence that
the condition of bodies at high temperatures is subject to important
physical changes.

The principle upon which the safety lamp is constructed is, that a
mixture of the fire-damp and atmospheric air in certain proportions
explodes upon coming in contact with a flame.

This mixture passes readily through a wire gauze, under all
circumstances, and it, of course, thus approaches the flame of the lamp
enclosed within such a material, and it explodes. But, notwithstanding
the mechanical force with which the exploding gas is thrown back
against the bars of its cage, it cannot pass them. Consequently, the
element of destruction is caught and caged; and notwithstanding its
fierceness and energy, it cannot impart to the explosive atmosphere
without, any of its force. No combustion can be communicated through
the wire gauze.

The researches which led to the safety-lamp may be regarded as among
the most complete examples of correct inductive experiment in the range
of English science, and the result is certainly one of the proudest
achievements of physico-chemical research. By merely enveloping the
flame of a lamp with a metallic gauze, the labourer in the recesses of
the gloomy mine may feel himself secure from that outpouring current
of inflammable gas, which has been so often the minister of death; he
may walk unharmed through the explosive atmosphere, and examine the
intensity of its power, as it is wasted in trifling efforts within the
little cage he carries. Accidents have been attributed to the “Davy,”
as the lamp is called among the colliers; but they may in most cases be
traced to carelessness on the part of those whose duty it has been to
examine the lamps, or to the recklessness of the miners themselves.

That curious metal, platinum, and also palladium, possesses a property
of maintaining a slow combustion, which the discoverer of the
safety-lamp proposed to render available to a very important purpose.
If we take a coil of platinum wire, and, having made it red-hot, plunge
it into an explosive atmosphere of carburetted hydrogen and common
air, it continues to glow with considerable brightness, producing,
by this very peculiar influence, a combination of the gases, which
is discovered by the escape of pungent acid vapours. Over the little
flame of the safety-lamp, it was proposed by Davy to suspend a coil
of platinum which would be thus kept constantly at a red heat. If the
miner became accidentally enveloped in an atmosphere of fire-damp,
although the flame of his lamp might be extinguished, the wire would
continue to glow with sufficient brightness to light him from his
danger, through the dark winding passages which have been worked in the
bed of fossil fuel. This very beautiful arrangement has not, however,
been adopted by our miners.

It is thus that the discoveries of science, although they may appear
of an abstract character, constantly, sooner or later, are applied to
uses by which some branch of human labour is assisted, the necessities
of man’s condition relieved, and the amenities of life advanced.

The respiration of animals is an instance of the same kind of chemical
phenomena as we discover in ordinary combustion. In the lungs the blood
becomes charged with oxygen, derived from the atmospheric air, with
which it passes through the system, performing its important offices,
and the blood is returned to the lungs with the carbonic acid formed
by the separation of carbon from the body which is thrown off at every
expiration. It will be quite evident that this process is similar to
that of ordinary combustion. In man or animals, as in the burning
taper,--which is aptly enough employed by poets as the symbol of
life,--we have hydrogen and carbon, with some nitrogen superadded; the
hydrogen and oxygen form water under the action of the vital forces;
the carbon with oxygen produces carbonic acid, and, by a curious
process, the nitrogen and hydrogen also combine, to form ammonia.[222]

All the carbon which is taken into the animal economy passes, in
the process of time, again into the atmosphere, in combination with
oxygen, this being effected in the body, under the _catalytic_ power of
tissues, immediately influenced by the excitation of nervous forces,
which are the direct manifestations of vital energy. The quantity of
carbonic acid thus given out to the air is capable of calculation,
with only a small amount of error. It appears that upwards of fifty
ounces of carbonic acid must be given off from the body of a healthy
man in twenty-four hours. On the lowest calculation, the population of
London must add to the atmosphere daily 4,500,000 pounds of carbonic
acid. It must also be remembered that in every process for artificial
illumination, and in all the operations of the manufactures in which
fire is used, and also in our arrangements to secure domestic comfort,
immense quantities of this gas are formed. We may, indeed, fairly
estimate the amount, if we ascertain the quantity of wood and coal
consumed, of all the carbon which combines with oxygen while burning,
and escapes into the air, either as carbonic acid or carbonic oxide.
The former gas, the same as that which accumulates in deep wells
and in brewers’ vats, is highly destructive to life, producing very
distressing symptoms, even when mixed with atmospheric air, in but
slight excess over that proportion which it commonly contains. The
oppressive atmosphere of crowded rooms is in a great measure due to the
increased proportion of carbonic acid given off from the lungs of those
assembled, and collected in the almost stagnant air of badly ventilated
apartments. It will be evident to every one, that unless some provision
was made for removing this deleterious gas from the atmosphere as
speedily as it formed, consequences of the most injurious character to
the animal races would ensue. It is found, however, that the quantity
in the atmosphere is almost constantly about one per cent. The peculiar
properties of carbonic acid in part ensure its speedy removal. It is
among the heaviest of gaseous bodies, and it is readily absorbed by
water; consequently, floating within a short distance from the surface
of the earth, a large quantity is dissolved by the waters spread
over it. A considerable portion is removed by the vegetable kingdom;
indeed, the whole of that produced by animals, and by the processes
of combustion, eventually becomes part of the vegetable world, being
absorbed with water by the roots, and separated from the air by the
peculiar functions of the leaves. However, this heavy gas unites with
the lighter atmospheric fluid in obedience to that law which determines
the diffusion of different specific gravities through each other.

The leaves of plants may be regarded as performing similar offices
to the lungs of animals. They are the breathing organs. In the animal
economy a certain quantity of carbon is necessarily retained, in
combination with nitrogen and other elements, to form muscle; but this
is constantly undergoing change; the entire system being renewed within
a comparatively limited period. The conditions with plants are somewhat
different. For instance, the carbon is fixed in a tree, and remains
as woody fibre until it decays, even though the life of the plant may
extend over centuries.

Animals, then, are constantly supplying carbonic acid; plants are as
constantly feeding on it; thus is the balance for ever maintained
between the two kingdoms. Another condition is, however, required to
maintain for the uses of men and animals the necessary supply of oxygen
gas. This is effected by one of those wonderful operations of nature’s
chemistry which must strike every reflecting mind with admiration.
During the night plants absorb carbonic acid; but there is a condition
of repose prevailing then in their functions, and consequently their
powers of effecting the decomposition of this gas are reduced to their
minimum. The plant sleeps, and vital power reposes; its repose being as
necessary to the plant as to the animal. With the first gleam of the
morning sun the dormant energies of the plant are awakened into full
action; it decomposes this carbonic acid, secretes the carbon, to form
the rings of wood which constitute so large a part of its structure,
and pour out oxygen gas to the air. The plant is, therefore, an
essential element in the conditions necessary for the support of animal
life.

The animal produces carbonic acid in an exact proportion to the
quantity of carbonaceous matter which it consumes. Fruit and herbage
contain a small quantity of carbon in comparison with muscle and fat.
But let us confine our attention to the human race. Man within the
Tropics, where the natural temperature is high, does not require so
great an amount of chemical action to go on within him for the purpose
of maintaining the requisite animal heat; consequently his Maker has
surrounded him with fruits and grains which constitute his food.

As we advance to the colder regions of the earth man becomes a
flesh-eater, and his carnivorous appetite increases as the external
temperature diminishes. Eventually we reach the coldest zones, and the
human being there devours enormous quantities of fat to supply the
necessities of his condition.

It must necessarily follow, that the inhabitants of the tropics do not
produce so much carbonic acid as those who dwell in colder regions. In
the first place, their habits of life are different, and they are not
under the necessity of maintaining animal heat by the use of artificial
combustion, as are the people of colder climes. The vegetation of
the regions of the tropics is much more luxuriant than that of the
temperate and arctic zones. Hence an additional supply of carbonic acid
is required between the torrid zones, and a less quantity is produced
by its animals. These cases are all met by the great aërial movements.
A current of warmed air, rich in oxygen, moves from the equator towards
the poles, whilst the cooler air, charged with the excess of carbonic
acid, sets in a constant stream towards the equator. By this means the
most perfect equalization of the atmospheric conditions is preserved.

The carbonic acid poured out from the thousand mouths of our fiery
furnaces,--produced during the laborious toil of the hard-working
artizan,--and exhaled from every populous town of this our island
home,--is borne away by this our aërial currents to find its place
in the pines of the Pacific Islands, the spice-trees of the Eastern
Archipelago, and the cinchonas of Southern America. The plants of
the valley of the Caucasus, and those which flourish amongst the
Himalayas, equally with the less luxuriant vegetation of our temperate
climes, are directly dependent upon man and the lower animals for their
supply of food.

If all plants were removed from the earth, animals could not exist.
How would it be if the animal kingdom was annihilated?--would it
be possible for vegetation to continue? This question is not quite
so easily answered; but, if we suppose all the carbon-producing
machines--the animals--to be extinct, from whence would the plants
draw their supply? It has been supposed that during the epoch of
the coal formation a luxuriant vegetation must have gone on over
the earth’s surface, when the existence of animal life was regarded
as problematical. It is supposed that the air was then charged with
carbonic acid, and that the calamites, lepidodendra, and sigilaria,
were employed to remove it, and fit the earth for the oxygen-breathing
races. The evidence upon these points is by no means satisfactory; and
although at one time quite disposed to acquiesce in a conjecture which
appears to account so beautifully for the observed geological phenomena
of carboniferous periods, we do not regard the necessities for such
a condition of the atmosphere as clearly made out.[223] Geological
research, too, has shown that the immense forests from which our coal
is formed teemed with life. A frog as large as an ox existed in the
swamps, and the existence of insects proves the high order of organic
creation at this epoch.

In all probability the same mutual dependence which now exists between
the animal and vegetable kingdoms existed from the beginning of time,
and will continue to do so under varying circumstances through the
countless ages of the earth’s duration.

There is yet another very important chain of circumstances which binds
these two great kingdoms together. This is the chain of the animal
necessities. A large number of races feed directly upon vegetables;
herbs and fruits are the only things from which they gain those
elements required to restore the waste of their systems.

These herbivorous animals, which must necessarily form fat and muscle
from the elements of their vegetable diet, are preyed on by the
carnivorous races; and from these the carbon is again restored to the
vegetable world. Sweep off from the earth the food of the herbivora,
they must necessarily very soon perish, and with their dissolution,
the destruction of the carnivora is certainly ensured. To illustrate
this on a small scale, it may be mentioned that around the coasts of
Cornwall, pilchards were formerly caught in very great abundance, in
the shallow water within coves, where these fish are now but rarely
seen. From the investigations of the Messrs. Couch, whose very accurate
observations on the Cornish fauna have placed both father and son
amongst the most eminent of British naturalists,[224] it appears that
the absence of these fish is to be attributed entirely to the practice
of the farmers, who cut the sea-weed from the rocks for the purpose
of manuring their lands. By this they destroy all the small crustacea
inhabiting these immature marine forests feeding on the algæ, and as
these, the principal food of the pilchards, have perished they seek
for a substitute in more favourable situations. Mr. Darwin remarks,
that if the immense sea-weeds of the Southern Ocean were removed by any
cause, the whole fauna of these seas would be changed.

We have seen that animals and vegetables are composed principally of
four elementary principles,--oxygen, hydrogen, nitrogen, and carbon.
We have examined the remarkable manner in which they pass from one
condition--from one kingdom of nature--into another. The animal,
perishing and dwindling by decomposition into the most simple forms of
matter, mingling with the atmosphere as mere gas, gradually becomes
part of the growing plant, and by like changes vegetable organism
progresses onward to form a portion of the animal structure.

A plant exposed to the action of natural or artificial decomposition
passes into air, leaving but a few grains of solid matter behind it.
An animal, in like manner, is gradually resolved into “thin air.”
Muscle, and blood, and bones, having undergone the change, are found to
have escaped as gases, leaving only “a pinch of dust,” which belongs
to the more stable mineral world. Our dependency on the atmosphere
is therefore evident. We derive our substance from it--we are, after
death, resolved again into it. We are really but fleeting shadows.
Animal and vegetable forms are little more than consolidated masses of
the atmosphere. The sublime creations of the most gifted bard cannot
rival the beauty of this, the highest and the truest poetry of science.
Man has divined such changes by the unaided powers of reason, arguing
from the phenomena which science reveals in unceasing action around
him. The Grecian sage’s doubts of his own identity, were only an
extension of a great truth beyond the limits of our reason. Romance and
superstition resolve the spiritual man into a visible form of extreme
ethereality in the spectral creations, “clothed in their own horror,”
by which their reigns have been perpetuated.

When Shakespeare made his charming Ariel sing--

    “Full fathom five thy father lies,
      Of his bones are coral made,
    Those are pearls that were his eyes:
      Nothing of him that doth fade,
    But doth suffer a sea change
    Into something rich and strange,”

he painted, with considerable correctness, the chemical changes
by which decomposing animal matter is replaced by a siliceous or
calcareous formation.

But the gifted have the power of looking through the veil of nature,
and they have revelations more wonderful than even those of the
philosopher, who evokes them by perpetual toil and brain-racking
struggle with the ever-changing elements around him.

The mysteries of flowers have ever been the charm of the poet’s song.
Imagination has invested them with a magic influence, and fancy has
almost regarded them as spiritual things. In contemplating their
surpassing loveliness, the mind of every observer is improved, and
the sentiments which they inspire, by their mere external elegance,
are great and good. But in examining the real mysteries of their
conditions, their physical phenomena, the relations in which they stand
to the animal world, “stealing and giving odours” in the marvellous
interchange of carbonic acid and ammonia for the soul-inspiring
oxygen--all speaking of the powers of some unseen, in-dwelling
principle, directed by a supreme ruler--the philosopher finds subjects
for deep and soul-trying contemplation. Such studies lift the mind into
the truly sublime of nature. The poet’s dream is the dim reflection of
a distant star: the philosopher’s revelation is a strong telescopic
examination of its features. One is the mere echo of the remote whisper
of nature’s voice in the dim twilight; the other is the swelling music
of the harp of Memnon, awakened by the sun of truth, newly risen from
the night of ignorance.

To return from our long, but somewhat natural digression, to a
consideration of the chemical phenomena connected with the atmosphere,
and its curious and important element, nitrogen, we must first examine
the evidence we have of the condition of the air itself.

The mean pressure exerted upon the surface of the earth, as indicated
by the barometer, is equal to a column of mercury thirty inches
high; that is, the column of air from the surface of the ocean to
its highest limits exactly balances that quantity of mercury. If our
tube of mercury had the area of one square inch, the columns would
weigh fifteen pounds, which represents a pressure of fifteen pounds
upon every square inch of the earth’s surface. This pressure, it must
be remembered, is the compound weight of the gaseous envelope, and
the elastic force of the aqueous vapour contained in it.[225] If the
atmosphere were of uniform condition, its height, as inferred from
the barometer, would be about five miles and a half. The density of
the air, however, diminishes with the pressure upon it, so that at the
height of 11,556 feet, the atmosphere is of half density; or one volume
of air, as taken at the surface of the earth, is expanded into two at
that height. Thus the weight is continually diminishing; but this is
regularly opposed by the decreasing temperature, which diminishes the
rate of about one degree for every 352 feet of ascent, although in all
probability it is less rapid at great distances from the earth.

It has been calculated from certain phenomena of refraction, that our
atmosphere must extend to about forty miles from the surface of the
earth. It may, in a state of extreme tenuity, extend still further;
but it is probable that the intense cold produced by rarefaction sets
limits to any extension much beyond this elevation.

The uses of the atmosphere are many. It is the medium for regulating
the dispersion of watery vapours over the earth. If there were no
atmosphere, and that, as now, the equatorial climes were hot and the
poles cold, evaporation would be continually going on at the equator,
and condensation in the colder regions. The sky of the tropical climes
would be perpetually cloudless, whilst in the temperate and arctic
zones we should have constant rain and snow. By having a gaseous
atmosphere, a more uniform state of things is produced; the vapours
arising from the earth become intimately mixed with the air, and are
borne by it over large tracts of country, and only precipitated when
they enter some stratum much colder than that which involves them.
There are opposite tendencies in an atmosphere of air and one of
vapour. The air circulates from the colder to the warmer parts, and
the vapour from the warmer to the colder regions; and as the currents
of the air, from the distribution of land and sea--the land, from its
low conducting power, being more quickly heated than the sea--are
very complicated, and as some force is employed in keeping the vapour
suspended in the air, water is less suddenly deposited on the earth
than it would have been, had not these tendencies of the air and its
hygrometric peculiarities been such as we find them.

The blue colour of the sky, which is so much more agreeable to the eye
than either red or yellow, is due to a tendency of the mixed gas and
vapour to reflect the blue rays rather than red or yellow. The white
light which falls upon the surface of the earth, without absorption or
decomposition in its passage from the sun, is partially absorbed by,
and in part reflected back from, the earth. The reflected rays pass
with tolerable freedom through this transparent medium, but a portion
of the blue rays are interrupted and rendered visible to us. That it
is reflected light, is proved by the fact of its being in a polarized
state.[226] Clouds of vapour reflect to us again, not isolated rays,
but the undecomposed beam, and consequently they appear white as snow
to our vision.

The golden glories of sunset,--when, “like a dying dolphin,” heaven
puts on the most gorgeous hues, which are continually changing,--depend
entirely upon the quantity of watery vapour which is mixed with air,
and its state of condensation. It has been observed, that steam at
night, issuing into the atmosphere under a pressure of twenty or thirty
pounds to the square inch, transmits and reflects orange-red light.
This we may, therefore, conclude to be the property of such a condition
of mixed vapour and air, as prevails when the rising or the setting
sun is shedding over the eastern or the western horizon the glory of
its  rays.[227]

Thus science points out to us the important uses of the air. We learn
that life and combustion are entirely dependent on it, and that it
is made the means for securing greater constancy in the climates
of the earth than could otherwise be obtained. The facts already
dwelt upon are sufficient to convince every thinking mind that the
beautiful system of order which is displayed in the composition of
the atmosphere, in which the all-exciting element, oxygen, is subdued
to a tranquil state by another element, nitrogen, (which, we shall
have presently to show, is itself, under certain conditions, one of
the most energetic agents with which we are acquainted,) indicates a
supreme power, omniscient in the adaptation of things to an especial
end. Oxygen and nitrogen are here _mixed_ for the benefit of man;
man _unites_ them by the aid of powers with which he is gifted, and
the consequences are of a fatal kind. The principles which the great
Chemist of Nature renders mild are transformed into sources of evil by
the chemist of art.

Beyond all this, the atmosphere produces effects on light which add
infinitely to the beauty of the world. Were there no atmosphere, we
should only see those objects upon which the sun’s rays directly fell,
or from which they were reflected. A ray falling through a small hole
into a dark room, illuminating one object, which reflects some light
upon another, is an apt illustration of the effect of light upon
the earth, if it existed without its enveloping atmosphere. By the
dispersive powers of this medium, sunlight is converted into daylight;
and instead of unbearable, parallel rays illuminating brilliantly,
and scorching up with heat those parts upon which they directly
fall, leaving all other parts in the darkness of night, we enjoy the
blessings of a diffusion of its rays, and experience the beauties of
soft shades and slowly-deepening shadows. Without an atmosphere, the
sun of the morning would burst upon us with unbearable brilliancy, and
leave us suddenly, at the close of day, at once in utter darkness. With
an atmosphere we have the twilight with all its tempered loveliness,--a
“time for poets made.”

In chemical character, atmospheric air is composed of twenty-one
volumes of oxygen, and seventy-nine volumes of nitrogen: or one hundred
grains of air consist of 23·1 grains of the former, and 76·9 grains
of the latter. Whether the air is taken from the greatest depths or
the most exalted heights to which man has ever reached, an invariable
proportion of the gases is maintained. The air of Chimborazo, of the
arid plains of Egypt, of the pestilential delta of the Niger, or
even of the infected atmosphere of an hospital, all give the same
proportions of these two gases as we find existing on the healthful
hills of Devonshire, or in the air of the city of London. This
constancy in constitution leads to the supposition that the oxygen
and nitrogen are chemically combined; but many eminent philosophers
have contended that they are merely mechanically mixed; and they have
shown that some peculiar properties prevail amongst gaseous bodies,
which very fully explain the equal admixture of two gases the specific
gravities of which are different. This is particularly exemplified in
the case of carbonic acid, of which gas one per cent. can be detected
in all regions of the air to which the investigations of man have
reached. This gas, although so heavy, is, by the law of diffusion,
mixed with great uniformity throughout the mass.[228] Every exhalation
from the earth, of course, passes into the air; but these are generally
either so light that they are carried into the upper regions, and
there perform their parts in the meteorological phenomena, or they
are otherwise very readily absorbed by water or growing plants, and
thus is the atmosphere preserved in a state of purity for the uses of
animals. Again, the quantity of oxygen contained in the air, and its
very peculiar character, ensures the oxidation of all the volatile
organic matters which are constantly passing off,--as the odoriferous
principles of plants, the miasmata of swamps, and the products of
animal putrefaction; these are rapidly converted into water, carbonic
acid, or nitric acid, and quickly enter into new and harmless
combinations. The elements of contagion we are unacquainted with; but
since the attention of inquirers has been of late directed to this
important and delicate subject, some light may possibly be thrown upon
it before long.

Nothing, shows more strikingly the admirable adaptation of all things
for their intended uses than the atmosphere. In it we find the source
of life and health; and chemistry teaches us, most indisputably,
that it is composed of certain proportions of oxygen and nitrogen
gases; and experience informs us that it is on the oxygen that we
are dependent for all that we enjoy. So beautifully is the atomic or
molecular constitution ordered, that it is impossible to produce any
change in the air without rendering it injurious to the vegetable and
animal economy. It might be thought, from the well-known exhilirating
character of oxygen gas, that, if a larger quantity existed in the
atmosphere than that which we find there, the enjoyments of life would
be of a more exciting kind; but the consequences of any increase would
be exceedingly injurious; and, by quickening all the processes of life
to an unnatural extent, the animal fabric would soon decay: excited
into fever, it would be destroyed by its own fires. Chemistry has made
us acquainted with six other compounds of oxygen and nitrogen, neither
of them fitted for the purposes of vitality, of which the following are
the most remarkable:--

Nitrous oxide, or the, so called, _laughing gas_, which contains two
volumes of nitrogen to one of oxygen, would prove more destructive than
even pure oxygen, from the delirious intoxication which it produces.

Nitric oxide is composed, according to Davy, of two volumes of nitrogen
and two of oxygen. It is of so irritating a nature, that the glottis
contracts spasmodically when any attempt is made to breathe it; and the
moment it escapes into the air it combines with more oxygen, and forms
the deep red fumes of nitrous acid.

Nitrous acid and the peroxide of nitrogen each contains an additional
proportion of oxygen, and they are still more destructive to all
organization.

Nitric acid contains five volumes of oxygen united to two of nitrogen;
and the well-known destructive properties of aqua fortis it is
unnecessary to describe.

The atmosphere, and these chemically active compounds, contain the same
elements, but their mode of combining is different; and what is, in the
one case, poisonous to the highest degree, is, in the other, rendered
salubrious, and essential to all organized beings.

Nitrogen gas may be regarded in the light of a diluent to the oxygen.
In its pure state it is only characterised by its negative properties.
It will not burn, or act as a supporter of combustion. Animals speedily
perish if confined in it; but they die rather through the absence
of oxygen than from any poisonous property of this gas. Yet, in
combination, we find nitrogen exhibiting powers of a most energetic
character. In addition to the fulminating compounds and the explosive
substances already named, which are among the most remarkable instances
of unstable affinity with which we are acquainted, we have also the
well-known pungent body, ammonia. From the analogous nature of this
volatile compound, and the fixed alkalies soda and potash, it was
inferred that it must, like them, be an oxide of a metallic base. Davy
exposed ammonia to the action of potassium, and to the influence of the
voltaic arc produced from 2,000 double plates, without at all changing
its character. From its slight tendency to combination, and from its
being found abundantly in the organs of animals feeding on substances
that do not contain it, it is, however, probably a compound body. A
phenomenon of an obscure and mysterious character is presented in the
formation of the “ammoniacal amalgam,” as it is called.

Mercury, being mixed with an ammoniacal salt, is exposed to powerful
galvanic action; and a compound, maintaining its metallic appearance,
but of considerable lightness and very porous, presents itself.[229]
This preparation has been carefully examined by Davy, Berzelius, and
others. It is always resolved into ammonia and mercury; and, although
the latter chemist is strongly inclined to regard it as affording
evidence of the compound nature of nitrogen,--and he has, indeed,
proposed the name _nitricum_ for its hypothetical base,--yet, to the
present time, we have no satisfactory explanation of this apparent
metallization of ammonia.

No attempt will be made to describe the various elementary substances
which come under the class of metallic bodies, much less to enumerate
their combinations. Many of the metals, as silver and copper, are found
sometimes in a native state, or nearly pure; but, for the most part,
they exist, in nature, in combination with oxygen or sulphur; gold
furnishing a remarkable exception. They are occasionally found combined
with other bodies,--as oxidized carbon, phosphorus, chlorine, &c.; but
these cases are by no means so common. Those substances called metals
are generally found embedded in the rocks, or deposited in fissures
formed through them; but it is one of the great discoveries of modern
science, that those rocks themselves are metallic oxides. With metals
we generally associate the idea of great density; but potassium and
sodium, the metallic bases of potash and soda, are lighter than water,
and they consequently float upon that fluid. We learn, therefore, from
the researches of science, that the crust of this earth is composed
entirely of metals, combined with gaseous elements; and there is
reason for believing that one, or perhaps two, of the gases we have
already named are also of a metallic character. Strange as it may
appear, there is nothing, as will be seen on attentive consideration,
irrational in this idea. Many of the metals proper, under the influence
of such heat as we can, by artificial means, command, are dissipated
in vapour, and may be maintained in this state perfectly invisible.
Indeed, the transparent space above the surface of the mercury in the
tube of a barometer, known as the Torricellian vacuum, is filled with
the vapour of mercury. There is, therefore, no reason why nitrogen,
or even hydrogen, should not be metallic molecules kept by the force
of the repulsive powers of heat, or some other influence, at a great
distance from each other. The peculiar manner in which nitrogen unites
with mercury, and the property which hydrogen possesses of combining
with antimony, zinc, arsenic, potassium, sodium, and possibly other
metals, besides its union with sulphur and carbon--in all which cases
there is no such change of character as occurs when they combine with
oxygen--appear to indicate bodies which, chemically, are not very
dissimilar to those metals themselves, although, physically, they have
not the most remote resemblance.

“We know nothing,” says Davy, “of the true elements belonging to
nature; but, so far as we can reason from the relations of the
properties of matter, hydrogen is the substance which approaches
nearest to what the elements may be supposed to be. It has energetic
powers of combination, its parts are highly repulsive as to each
other, and attractive of the particles of other matter; it enters into
combination in a quantity very much smaller than any other substance,
and in this respect it is approached by no known body.”[230]

Many of the elements are common to the three kingdoms of nature:
most of those found in one condition of organization are discovered
in another. The carbonates are an abundant mineral class. In the
vegetable kingdom we find carbon combining with oxygen, hydrogen, and
nitrogen: these elements, also, constitute the substance of animals,
the proportion of nitrogen being, however, much larger. If one element,
more than another, belongs especially to the animal economy, it is
phosphorus, although this is not wanting in the vegetable world; and
it is not uncommon in the mineral. Sulphur is common to the three
kingdoms: it is abundant in the mineral, being one of the products of
volcanic action; it is united with the metals, forming sulphurets;
and is found in our rocks in the state of sulphuric acid or oxidized
vapour, combined with the metallic bases of lime and other earths. In
the vegetable kingdom we discover sulphur in all plants of the onion
kind, in the mustard, and some others; it enters into the composition
of vegetable albumen, and appears always combined with albumen,
fibrine, and caseine, in the animal economy.

Chlorine is found most abundantly in combination with sodium, as common
salt: in this state, in particular, we may trace it from the depths
of the earth, its waters, and its rocks, to the plants and animals
of the surface. Iodine is most abundant in marine plants; but it has
been found in the mineral world, traced to plants, and it is indicated
in the flesh of some animals. Bromine is known to us as a product of
certain saline waters, and a few specimens of natural bromide of silver
have been examined. Fluorine, the base of the acid which, combining
with lime, forms fluor-spar, is found to exist to some considerable
extent in bones; it has been discovered in milk and blood; and
investigations have proved its existence in the vegetable world. It
must not be forgotten that the earths, lime and magnesia, enter into
the composition of the more solid parts of plants and animals. Lime is
one of the principal constituents of animal bone and shells, and it is
found in nearly all vegetables.

Silica, or the _earth_ of flints, is met with in beautiful transparent
crystals, in the depths of the mine; in all rock and soils we find it.
In the bark of many plants, particularly the grasses, it is discovered,
forming the hard supporting cuticle of the stalk, in wheat, the Dutch
rush, the sugar-cane, the bamboo, and many other plants.

It is thus that we find the same elementary principle presenting itself
in every form of matter, under the most Protean shapes. Numerous
phenomena of even a more striking character than those selected, are
exhibited in every department of chemistry; but within the limits of
this essay it is impracticable to speak of any beyond those which
directly explain natural phenomena.

The chemical elements, which actually exist in nature as simple
bodies, are probably but few. Most of the gases are in all probability
compounds of some ethereal ultimate principles; and with the advance of
science we may fairly hope to discover the means of reducing some of
them to a yet more simple state.

Curious relations, which can be traced through certain bodies, lead us
to believe that they may be only modified conditions of one element.
Flint and charcoal do not at first appear allied; but carbon in some
of its states approaches very near to the condition of silicon, the
metallic base of flint. When we remember the differences which are
evident in three forms of one body--coke, graphite, and diamond--the
dissimilitude between flint, a quartz crystal, and carbon, will cease
to be a strong objection to the speculation.

Phosphorus, sulphur, and selenium, have many properties in common.
Iodine, bromine, chlorine, and fluorine, appear to belong to the same
group. Iron and nickel, and cobalt, have a close relation. Silver and
lead are usually combined, and exhibit a strong relationship. Gold,
platinum, and the rarer metals, have so many properties in common, that
they may form a separate group from all the others.

Indeed, a philosophical examination of the elements now supposed to
constitute the material world, enables us to divide them into about six
well-defined groups. Wide differences exist within these groups; but
still we find a sufficient number of common properties to warrant our
classing them in one family.

The dream of the alchemists, in the vain endeavour to realise which
they exhausted their lives and dissipated their wealth, had its
foundation in a natural truth. The transmutation of one form of matter
into another may be beyond the power of man, but it is certainly
continually taking place in the laboratory of nature, under the
directing law of the great Creator of this beautiful earth.

The speculations of men, through all ages, have leaned towards this
idea, as is shown by the theory of the four elements,--Air, Fire,
Earth, and Water,--of the ancients, the three,--Salt, Sulphur, and
Mercury,--of the alchemists, and the refined speculations of Newton
and Boscovich on the ultimate constitution of matter. All experimental
inquiry points towards a similar conclusion. It is true we have no
direct evidence of any elementary atom actually undergoing a change
of state; but when we regard the variations produced by electrical
influence, the changes of state which arise from the power of heat, and
the physical alterations produced by light, it will be difficult to
come to any other conclusion than that the particles of matter known
to us as ultimate are capable of change, and consequently must be far
removed from positively simple bodies, since the real elementary atom,
possessing fixed properties, cannot be supposed capable of undergoing
any transmutation. Allotropism could not occur in any absolutely simple
body.

It will now be evident that in all chemical phenomena we have the
combined exercise of the great physical forces, and evidences of some
powers which are, as yet, shrouded in the mystery of our ignorance. The
formation of minerals within the clefts of the rocks, the decomposition
of metallic lodes, the germination of seeds, the growth of the plant,
the development of its fruit and its ultimate decay, the secret
processes of animal life, assimilation, digestion, and respiration, and
all the changes of external form, which take place around us, are the
result of the exercise of that principle which we call chemical.

By chemical action plants take from the atmosphere the elements of
their growth; these they yield to animals, and from these they are
again returned to the air. The viewless atmosphere is gradually formed
into an organized being, the lordly tree upon whose branches the fowls
of the air have their homes, and the human animal, exalted by being
charged with a spiritual soul: yet the tree and the man alike are
gradually resolved again into thin air. The changes of the mineral
world are of an analogous character; but we cannot trace them so
clearly in all their phenomena.

The planet on which we live began its course charged with a fixed
quantity of physical force, and this has remained constant to the
present moment, and will do so to the end of time. By influences
external to this earth the balance of these forces is continually
disturbed; and in the effort to restore the equilibrium, we have the
production of all the varied forms of matter, and the manifestation of
each particular physical principle or power. As motion and attraction,
balanced against each other, maintain the earth in her elliptical
orbit, so the opposition of forces determines the existence of the
amorphous rock, the light-refracting crystal, the fixed and flowering
plant, and the locomotive animal.

An eternal round of chemical action is displayed in nature. Life and
death are but two phases of its influences. Growth and decay are
equally the result of its power.


FOOTNOTES:

[212] Dr. Priestley appears to have been the first to observe the
peculiar property of the diffusion of gases. Dr. Dalton, however,
first drew attention to the important bearing of this fact on natural
phenomena, and he published his views on _The Miscibility of Gases_ in
the Manchester Memoirs, vol. v. The following extract from his memoir
_On the Constitution of the Atmosphere_ will exhibit its bearings:--

It may be worth while to contrast this view of the constitution of the
atmosphere with the only other one, as far as I know, that has been
entertained.

    According to one view,        | According to the other view,
                                  |
    1. The volumes of each gas    | 1. The volume of each gas
    found at the surface of the   | found at the surface of
    earth are proportional to     | the earth, _multiplied by
    the whole weights of the      | its specific gravity_, is
    respective atmospheres.       | proportional to the whole
                                  | weight of the respective
                                  | atmospheres.
                                  |
        Azote           79        |     Azote           76·6
        Oxygen          21        |     Oxygen          23·4
        Aqueous vapour   1·33     |     Aqueous vapour   0·83
        Carbonic acid    1·0      |     Carbonic acid    0·15
                      -------     |                    ------
                      101·43      |                    100·88
                                  |
    2. The altitude of each       | 2. The altitude of each
    atmosphere differs from that  | atmosphere is the same, and
    of every other, and the       | the proportion of each in the
    proportions of each in the    | compound atmosphere, is the
    compound atmosphere gradually | same at all elevations.
    vary in the ascent.           |
                                  |
    3. When two atmospheres are   | 3. When two atmospheres
    mixed, they take their places | are mixed, they continue
    according to their specific   | so without the heavier
    gravity, not in separate      | manifesting any disposition to
    strata, but intermixedly.     | separate and descend from the
    There is, however, a separate | lighter.
    stratum of the specifically   |
    lighter atmosphere at the     |
    summit over the other.        |

[213] The discussion of this question, commenced by Arago in his
_Eloge_, was continued by Lord Brougham in his _Lives of Watt and
Cavendish_, and by Mr. Vernon Harcourt, in his address as President
of the British Association, and more recently in his _Letter to Lord
Brougham_. Watt’s _Letters_ on the subject have been since published
under the superintendence of Mr. Muirhead.

[214] See several papers _On Ozone_, by Professor Schönbein, in the
Philosophical Magazine, and in the Reports of the British Association.
Consult a paper by the Author: _Athenæum_, September, 1849.

[215] Memoire _sur l’Ozone_; Bàle 1849. Poggendorff’s _Annalen_,
lxxvii., p. 592. Ibid, lxxviii. p. 162.

[216] _Chemical Gazette_, 1849.

[217] Iodide of silver has been found at Albarradon, near Mazapil, in
Mexico. Iodide of mercury, of a fine lemon-yellow colour, has been
discovered in the sandstone of Casas, Viegas, Mexico. Algers; Phillips’
_Mineralogy_.

[218] GENTELE’S Reports of the Stockholm Academy.

[219] Stahl, taking up the obscure notions of Becher and Van Helmont,
supposed the phenomena of combustion to be due to phlogiston. He
imagined that by combination with phlogiston, a body was rendered
combustible, and that its disengagement occasioned combustion, and
after its evolution there remained either an acid or an earth: thus
sulphur was, by this theory, supposed to be composed of phlogiston and
sulphuric acid, and lead of the calx of lead and phlogiston, &c.

[220] Being called upon by the Solicitor for the Admiralty to examine
into the causes of the fire which destroyed the _Imogene_ and
_Talavera_, in Devonport Arsenal, I discovered a bin under the roofing
which covered these ships, in which there had been accumulating for a
long period all the refuse of the wheelwrights’ and painters’ shop; and
it was quite evident that spontaneous combustion had taken place in the
mass of oiled oakum, sawdust, anti-attrition, and old sail-cloth, there
allowed to accumulate.

[221] _Researches on Flame_: Sir H. Davy’s Collected Works.

[222] See note, _ante_, _On the Chemical Theory of Respiration_.

[223] At the request of the British Association, a committee undertook
the investigation of this subject. Experiments were carried on by Dr.
Daubeny, in the Botanic Gardens at Oxford, and by the Author, at his
residence, Stockwell. Dr. Daubeny, in his report made at the meeting
of the British Association at Birmingham, appears disposed to consider
ten per cent. of carbonic acid in excess as destructive to the growth
of ferns. I found, however, that, by gradually increasing the quantity,
the ferns would live in an atmosphere still more highly charged with
carbonic acid.

[224] See memoir _On the Pilchard_, by Mr. Couch, in the Reports of the
Royal Cornwall Polytechnic Society.

[225] “This scale, in which the humidity of the air is expressed,
is the simple natural scale in which air at its maximum of humidity
(_i.e._, when it is saturated with vapour) is reckoned as = 100, and
air absolutely deprived of moisture as = 0; the intermediate degrees
are given by the fraction 100 × actual tension of vapour ÷ tension
required for the saturation of the air at its existing temperature.
Thus, if the air at any temperature whatsoever contains vapour of half
the tension, which it would contain if saturated, the degree is 50; if
three-fourths, then 75; and so forth. Air of a higher temperature is
capable of containing a greater quantity of vapour than air of less
temperature; but it is the proportion of what it does contain, to what
it would contain if saturated, which constitutes the measure of its
dryness or humidity. The capacity of the air to contain moisture being
determined by its temperature, it was to be expected that an intimate
connection and dependence would be found to exist between the annual
and diurnal variations of the vapour and of the temperature.”--Sabine,
_On the Meteorology of Toronto_; Reports of the British Association,
vol. xiii. p. 47. _The Temperature Tables_: by Prof. W. H. Dove;
Reports for 1847 should be consulted.

[226] Sir David Brewster’s _Optics_, and Memoirs in the Philosophical
Transactions. Sir John Herschel’s Treatise on _Light_, Encyclopædia
Metropolitana.

[227] _On the Colour of Steam under certain circumstances_: by
Professor Forbes; Philosophical Magazine, vol. xiv. p. 121, vol. xv.
p. 25. In the first paper the following remarks occur:--“I cannot
doubt that the colour of watery vapour under certain circumstances
is the principal or only cause of the red colour observed in clouds.
The very fact that that colour chiefly appears in the presence of
clouds is a sufficient refutation of the only explanation of the
phenomena of sunset and sunrise, having the least plausibility, given
by optical writers. If the red light of the horizontal sky were simply
complementary to the blue of a pure atmosphere, the sun ought to set
red in the clearest weather, and then most of all; but experience shows
that a lurid sunrise or sunset is _always_ accompanied by clouds or
diffused vapours, and in a great majority of cases occurs when the
changing state of previously transparent and colourless vapour may be
inferred from the succeeding rain. In like manner, terrestrial lights
seen at a distance grow red and dim when the atmosphere is filled
with vapour soon to be precipitated. Analogy applied to the preceding
observations would certainly conduct to a solution of such appearances;
for I have remarked that the existence of vapour of high tension is
by no means essential to the production of colour, though of course
a proportionally greater thickness of the medium must be employed to
produce a similar effect when the elasticity is small.”

[228] _On the Law of Diffusion of Gases_: by Thomas Graham, M.A.,
F.R.S., &c.; Edinburgh Philosophical Transactions, 1832. _Sur l’Action
Capillaire des Fissures, &c._: by Döbereiner; Annales de Chimie, xxiv.
332.

[229] _Electro-chemical Researches on the Decompositions of the Earths,
with observations on the Metals obtained from the Alkaline Earths,
and on the Amalgam procured from Ammonia_: by Sir Humphry Davy;
Philosophical Transactions, 1808, and collected works, vol. v. p. 102.

[230] _Elements of Chemical Philosophy_: by Sir H. Davy.




CHAPTER XIII.

TIME.--GEOLOGICAL PHENOMENA.

  Time, an element in Nature’s Operations--Geological
    Science--Its Facts and Inferences--Nebular Hypothesis
    applied--Primary Formations--Plutonic and Metamorphic
    Rocks--Transition Series--Palæozoic Rocks--Commencement of
    Organic Arrangements--Existence of Phosphoric Acid in Plutonic
    Rocks--Fossil Remains--Coal Formation--Sandstones--Tertiary
    Formations--Eocene, Miocene, and Pliocene Formations--Progressive
    changes now apparent--General Conclusions--Physics applied in
    explanation.


The influence of time, as an element, in producing certain structural
arrangements, by modifying the operations of physical force, under
whatever form it may be exerted, has scarcely been sufficiently
attended to in the examination of cosmical phenomena. Every particle
of matter is, as it were, suspended between the agencies to which
we have been directing our attention. Under the influences of the
physical powers, sometimes exerted in common, but often with a great
preponderance in favour of one of them, every accumulated heap of mud
or sand is slowly cohering, and assuming the form of a rock possessing
certain distinguishing features, as it regards lamination, cleavage, &c.

The minute particles of matter are necessarily but slightly influenced
by the physical forces: their action in accordance with the laws which
determine physical condition is manifested in an exceedingly modified
degree. But in all the operations of nature, what is deficient in
power is made up in time, and effects are produced during myriads
of ages, by powers far too weak to give satisfactory results by any
experiments which might be extended even over a century.

If, with the eye of a geologist, we take but a cursory glance over the
Earth, we shall discover that countless ages must have passed during
the progress of this planet to its present state. This is a fact
written by the finger of nature, in unmistakeable characters, upon the
mighty tablets of her mountains.

The superficial crust of the earth,--by which is meant only that film,
compared with its diameter, which is represented by a few miles in
depth--is composed of distinct mineral masses, exhibiting peculiar
physical conditions and a certain order of arrangement. These rocks
appear to have resulted from two dissimilar causes; in one class the
action of heat is evident, and in the other we have either the slow
deposition of matter suspended in water, or crystallization from
solution; an aqueous origin is indicated by peculiarities of formation
in all the more recent rocks.

There are few branches of science which admit of speculation to the
extent to which we find it carried in geology. The consequences of this
are shown in the popular character of the science. A few observations
are made over a limited area, and certain structural conditions are
ascertained, and at once the mind, “fancy free,” penetrates the
profound depths of the earth, and imagination, having “ample room
and verge enough,” creates causes by which every effect is to be
interpreted. Such students, generally ignorant of the first principles
of physics, knowing little of mineralogy, and less of chemistry, to
say nothing of palæontology, having none of the requisites for an
observer, boldly assume premises which are untenable, and think they
have explained a phenomenon,--given to the world a truth,--when they
have merely promulgated an unsubstantiated speculation, which may have
occasional marks of ingenuity, and but little else.

The carefully-made observations of those who, with unwearying industry,
have traversed hill and valley, marked and measured the various
characters, thicknesses, inclinations, and positions of rocks; who have
watched the influences of heat in changing, of water in wearing, and
the results of precipitation in forming, strata; who have traced the
mechanical effects of earthquake strugglings and of volcanic eruptions,
and, reasoning from an immense mass of accumulated facts, deduced
certain general conclusions,--are, however, of a totally different
character; and it is such observers as these who induced Herschel to
say truly, that “geology, in the magnitude and sublimity of the objects
of which it treats, undoubtedly ranks, in the scale of the sciences,
next to astronomy.”[231]

The origin of this planet is involved in great obscurity, which the
powers of the most gifted are unable to penetrate. It stands the work
of an Almighty and Eternal mind, the beginning of which we cannot
comprehend, nor can we define the period of its termination.

It may, probably, be safe to speculate that there was a time when
this globe consisted of only one homogeneous stratum. Whether
this remains,--whether, in our plutonic rocks, our granites, or
our porphyries, we have any indications of the primitive state of
the world, or whether numerous changes took place before even our
unstratified formations had birth, are questions we cannot answer. The
geologist looks back into the vista of time, and reckons, by phenomena,
the progress of the world’s mutations. The stratified formations
must have occupied thousands of ages; but before these were, during
a period extending over countless thousands, the unstratified rocks
may have been variously metamorphosed. It matters not whether we admit
the nebular hypothesis or not,--a time must have been when all these
bodies which now form the mass of this globe existed in the most simple
state. We have already shown that very remarkable changes in external
character and in chemical relations are induced, in the same simple
element, by its having been exposed to some peculiar and different
conditions; and already have we speculated on the probability that
the advance of science will enable us to reduce the numerous elements
we now reckon, to two or three. It is, therefore, by no means an
irrational thought (which must, however, be held in the light of a
pure conjecture), to suppose that at the beginning a mighty mass of
matter, in the most attenuated state, was produced in space, and was
gradually, under the influence of gravitation, of cohesive force, and
of chemical aggregation, moulded into the form of a sphere. Ascending
to the utmost refinement of physics, we may suppose that this mass was
of one uniform character, and that it became in dissimilar parts--its
surfaces and towards its centre--differently constituted, under the
influences of the same powers which we now find producing, out of the
same body, charcoal and the diamond, and creating the multitudinous
forms of organized creations. These conditions being established, and
carried to an extent of which, as yet, science has afforded us no
evidence, chemical intermixture may have taken place, and a new series
of compounds have been formed, which, by again combining, gave rise to
another and more complex class of bodies.

The foundation of the superficial crust of the earth appears to be
formed of a class of rocks which have resulted from the slow cooling
of an immense mass of heated matter. These rocks have been called
_igneous_; but are now more generally termed _Plutonic_ (such as
granites, syenites, &c.) Immediately above these, we find rocks which
have resulted by deposition from water. These masses, having been
exposed to the action of the heat below, have been considerably changed
in their character, and hence they are often called _metamorphic_;
but metamorphic rocks may, however, be of any age. The rocks formerly
termed the _transition_ series--from their forming the connecting link
between the earlier formations--are now, from the circumstance of their
being fossiliferous, classed under the general term of palæozoic rocks,
to distinguish them from the rocks in which no organic remains have
been found. Above these are found the secondary strata, and, still more
recently produced, we have a class now usually denominated the tertiary
formations. “Eternal as the hills” is a poetic expression, implying a
long duration; but these must, from the nature of things, eventually
pass away. The period of time necessary for the disintegration of a
granite hill is vastly beyond the powers of computation, according
to our conception of the ordinary bounds of finite things. But a
consideration of the results of a few years,--under the influence of
the atmosphere and the rains,--as shown in quantity of solid matter
carried off by the rivers, and deposited at their mouths, will tend to
carry conviction to every mind, that a degrading process is for ever in
action on the surface of the earth. The earth itself may be eternal,
but the surface is continually undergoing mutation, from various
causes, many of which we must briefly consider.[232]

In regarding geological phenomena, the absence of any fossil remains
has often been supposed to indicate a period previous to any organic
formations. The inorganic constituents of matter are probably of
prior origin to the organic combinations; the vessel was constructed,
upon which the organic creation was to float in space before any
vital organisms were created. The supposed evidences in favour of the
assumption that there was no organic life during the formation of the
oldest rocks we know, are in some respects doubtful; and we can well
understand that changes may have been induced in the earlier rock
formations, by heat or by other powers, quite sufficient to destroy all
traces of organized forms. It was long thought that phosphoric acid was
not to be detected in rocks which are regarded as of igneous origin;
and since this acid is peculiarly a constituent of organic bodies, this
has been adduced as a proof that the plutonic rocks must have existed
previously to the appearance of vegetable or animal life upon the
surface of the globe. The researches of modern chemists have, however,
shown that phosphoric acid is to be found in formations of granitic
origin, in porphyry, basalt, and hornblende rocks.[233] If, therefore,
we are to regard this substance as of organic origin, the rational
inference is against the speculation; but there is no more necessity
for supposing phosphorus to be formed in the animal economy than in
the mineral kingdom, from which it will probably be found the animal
obtained it.

Without attempting to enter into any account of the apparent progress
of life over the earth, it appears desirable that some description
should be given of the kinds of plants and animals which we know to
have existed at different epochs. We shall thus learn, at least, some
of the prevailing characteristics of the earth during its transitions,
and be in a better condition for applying our knowledge of physical
power to the explanation of the various geological phenomena.

Among the earliest races we have those remarkable forms, the
trilobites, inhabiting the ancient ocean.

These crustacea bear some resemblance, although a very remote one, to
the common wood-louse, and, like that animal, they had the power of
rolling themselves into a ball when attacked by an enemy. The eye of
the trilobite is a most remarkable organ; and in that of one species,
_Phacops caudatus_, not less than two hundred and fifty lenses have
been discovered. This remarkable optical instrument indicates that
these creatures lived under similar conditions to those which surround
the crustacea of the present day.

At the period of the trilobites of the Silurian rocks, all the animals
contemporaneous with them had the organs necessary for the preservation
of life in the waters.

Next in order of time to the trilobite, the most singular animals
inhabiting those ancient seas, whose remains have been preserved,
are the _Cephalopoda_, possessing some traces of organs which belong
to vertebrated animals. There are numerous arms for locomotion and
prehension, arranged in a centre round the head, which is furnished
with a pair of sharp, horny mandibles, embedded in powerful muscles.
These prehensile arms are provided with a double row of suckers, by
which the animal seized its prey. Of these cephalopodous animals there
are many varieties, but all of them appear to be furnished with powers
of rapid locomotion, and those with shells had an hydraulic arrangement
for sinking themselves to any depth of the seas in which, without
doubt, they reigned the tyrants.

Passing by without notice the numerous fishes, which appear to have
exhibited a similar order of progression to the other animals, we must
proceed to the more remarkable period when the dry land first began to
appear.

All the animals found in the strata we have mentioned are such as would
inhabit the seas; but we gradually arrive at distinct evidence of the
separation of the land from the water, and the “green tree yielding
seed” presents itself to our attention; not that the strata earlier
than this are entirely destitute of any remains indicating vegetable
growth, but those they exhibit are such as, in all probability, may be
referred to marine plants.

Those plants, however, which are found in the carboniferous series
are most of them distinguished by all the characteristics of those
which grow upon the land; we, therefore, in the mutilated remains of
vegetation left us in our coal-formations, read the history of our
early world.

Then the reed-like calamite bowed its hollow and fragile stems over
the edges of the lakes the tree-ferns grew luxuriantly in the shelter
of the hills, and gave a wild beauty to the humid valleys; the
lepidodendrons spread themselves in mighty forests along the plains,
which they covered with their curious cones; whilst the sigillariæ
extended their multitudinous branches, wreathing like serpents amongst
the luxurious vegetation, and embraced, with their roots (stigmariæ), a
most extensive space on every side.[234]

The seas and lakes of this period abounded with minute animals nearly
allied to the coral animals, which are now so actively engaged in the
formation of islands in the tropical and southern seas. During the ages
which passed by without any remarkable disturbance of the surface of
the earth, the many bands of mountain limestone were formed by the
ceaseless activity of these minute architects. Encrinites (creatures
in some respects resembling star-fish) existed in vast numbers in the
oceans of this time; and the great variety of bivalve shells, and those
of a spiral character, discovered in the rocks of this period, show the
waters of the newer palæozoic period to have been instinct with life.

In the world then, as it does now, water acting on the dry land
produced remarkable changes. We have evidence of extensive districts
over which the most luxuriant vegetation must have spread for
ages,--from the remains of plants in every state of decay,--which we
find went to form our great coal-fields. These, by some changes in the
relative levels of land and water, became covered with this fluid;
and over this mass of decaying organic matter, sand and mud were for
ages being deposited. At length, rising above the surface, it becomes
covered with vegetation, which is, after a period, submerged; the same
deposition of sand and mud again takes place, it is once more fitted
for vegetable growth, and thus, cycle after cycle, we see the dry land
and the water changing places with each other. This will be evident
to every one who will carefully contemplate a section of one of the
coal-fields of Great Britain. We find a stratum of coal lying upon
a bed of under clay, and above it an extensive stratum of shale or
sandstone, probably formed by the denudation of the neighbouring hills;
and in this manner we have many strata of coal, shale, clay, ironstone,
and sandstone alternating with each other; the coal-formations of the
South Wales coal-field having the extraordinary thickness of 1500 feet.
The lowest bed of this extensive series must at one time have been
exposed as the surface of the country.

Ascending in the series, we have now formations of a more recent
character, in which fishes of a higher order of organization, creeping
and flying saurians, crocodiles and lizards, tortoises, serpents, and
frogs, are found. The lias formations (a term corrupted from _layers_),
consisting of strata in which an argillaceous character prevails, stand
next in series. In these we have animals preserved in a fossil state,
of a distinguishingly different character from those of the inferior
strata. We meet with extended beds of pentacrinites, some inches in
thickness; and their remains are often so very complete that every part
of the skeleton can be made out, although so complicated that it cannot
consist of less than 150,000 parts. In these formations we often find
the curiously beautiful remains of the ammonites, of which a great
variety have been discovered. Of the belemnites--animals furnished with
the shell and the ink-bag of the cuttle-fish, with which it darkened
the water to hide itself from enemies, numerous varieties have also
been disentombed, with the ink-bag so well preserved, that the story of
the remarkable fossil has been written with its own ink. In addition to
these we find nautili; and sixty species of extinct fishes have been
described by Agassiz from the lias of Lyme Regis alone.

When these rocks were in the progress of formation, there existed the
ichthyosaurus, or fish-lizard, which appears, in many respects, to have
resembled the crocodile of the Nile. It was a predatory creature of
enormous power, and must have been the tyrant and terror of the seas
which it inhabited. Its alligator-like jaws, its powerful eye, its
fish-like fins, and turtle-like paddles, were all formed to facilitate
its progress as a destructive minister. The plesiosaurus was, if
possible, a still more extraordinary creation. To the head of a lizard
was united an enormously long neck, a small and fish-like body, and the
tail of a crocodile: it appears formed for existence in shallow waters,
so that, when moving at the bottom, it could lift its head above the
surface for air, or in search of its food. The flora of this period
must have been extensive; and it resembled the vegetation which exists
at present in Tropical regions.

We pass now to a new epoch, which is well distinguished by its animals
from all that had preceded it. Races of reptiles still have place upon
the earth, and we have now the megalosaurian remains; these animals
possessing a strength and rapacity which would render them objects of
terror as well as astonishment, could they be restored to the world
which they once ravaged. An enormous bat-like creature also existed
at this time--the pterodactyl--which, in the language of Cuvier, was,
“undoubtedly, the most extraordinary of all the beings of whose former
existence a knowledge is granted to us, and that which, if seen alive,
would appear most unlike anything that exists in the present world.”
“You see before you,” says the same writer, “an animal which, in all
points of bony structure, from the teeth to the extremities of the
nails, presents the well-known saurian characteristics, and of which no
one can doubt that its integuments and soft parts, its scaly armour and
its organs of circulation and reproduction, are likewise analogous. But
it was, at the same time, an animal provided with the means of flying;
and, when stationary, its wings were probably folded back like those
of a bird, although, perhaps, by the claws attached to its fingers, it
might suspend itself from the branches of trees.”[235]

From the disintegration of the older rocks have no doubt arisen those
formations which are known as the oolitic series. In these strata are
preserved the remains of plants and animals more resembling those which
now exist upon the earth; and, for the first time,--unless the evidence
of the footsteps of birds on the new red sandstone of America be
accepted,--we meet with the remains of the feathered tribes.

In these formations we discover animals belonging to the class
Mammalia,--the amphitherium and the phascolotherium,--which appear
to have resembled, in many respects, the marsupial animals of New
Holland.[236]

The wealden formations, which are the next in order of position, are a
series of clays and sands, with subordinate beds of limestone, grit,
and shale. These have, in some instances, been formed in the sea; but
they are usually regarded as fresh-water deposits. All the older rocks
bear evident marks of marine origin, unless some of the coal-measure
strata may be regarded as otherwise; but nearly all the wealden series
contain the remains of land, fresh-water, and estuary animals, and of
land vegetables. The creatures which we discover, preserved, to tell
the history of this period, are numerous, and have marked peculiarities
to distinguish them from those already described, or from any now
existing on the earth. We find land saurians of a large kind, and
animals of all sizes; even insects, of which a great variety are found
in the wealds. The remarkable iguanodon was an animal which, even by
the cautious measurement of Professor Owen, must have been at least
twenty-eight feet long; and this enormous creature was suspected, by
Cuvier, and has been proved by Owen, to have been an “herbivorous
saurian for terrestrial life.”[237] Dr. Mantell calculates that no
less than seventy individuals of the iguanodon of all ages have come
under his notice; and the bones of a vast number of others must have
been broken up by the workmen in the few quarries of Tilgate grit;
so that these creatures were by no means rare at the period of their
existence.[238]

The uppermost of these secondary formations is the cretaceous or chalk
group, which spreads over a large portion of south-eastern England, and
is met with in all parts of Europe. This chalk, which is a carbonate
of lime, appears to have been slowly precipitated from tranquil water,
as, according to Sir Henry De la Beche, organic remains are beautifully
preserved in it. Substances of no greater solidity than common sponges
retain their forms, delicate shells remain unbroken, fish even are
frequently not flattened, and altogether we have the appearances
which justify us in concluding that, since these organic exuviæ were
entombed, they have been protected from pressure by the consolidation
of the rock around them.[239]

Beneath the chalk exists what has been called, from its colour--derived
from a silicate of the protoxide of iron,--green sand, and was, no
doubt, formed by deposition from the same water in which the carbonate
of lime was suspended,--the green sand falling to the bottom more
readily from its greater specific gravity. “The tranquillity,” observes
Sir Henry De la Beche, “which seems to have prevailed during this great
accumulation of siliceo-calcareous matter, whether it may have been
a deposit from water, in which it was mechanically suspended, partly
the work of living creatures, or in a great measure chemical, is very
remarkable.”[240]

In the chalk, the remains of the leaves of dicotyledonous plants
and fragments of wood are found more abundantly than in the earlier
strata, many of which are marked with the perforations of marine
worms, indicating that they had floated for some time in the ocean.
It should, however, be remembered, that these are not the first
indications of vegetable life,--leaves have been found in the new red
sandstone; and the flora of the coal formation must not be forgotten.
The manner in which silica has deposited itself on organic bodies--such
as the sponges--is curious; the whole of the organized tissue being
often removed, and flint having taken its place. Flints formed by
such a process as this abound in the upper chalk. The association
of carbon and silicon, combined with oxygen, as we find them in the
cretaceous formations, is most interesting, and naturally gives rise
to some speculation on the relation of these two elements. Both carbon
and silicon, as has been already shown, exist in several allotropic
conditions; and, although the statements made by Dr. Brown relative
to the conversion of carbon into silicon are proved to be grounded on
experimental error, it is not improbable that a very intimate relation
may exist between these elements.[241] The probability is, that the
sponge animal has the power of secreting silica to give strength
to its form. “Many species,” says Rymer Jones, speaking of recent
sponges, “exhibiting the same porous structure, have none of the
elasticity of the officinal sponge--a circumstance which is due to the
difference observable in the composition of their skeletons or ramified
frame-work. In such the living crust forms within its substance
not only tenacious bands of animal matter, but great quantities of
crystallized spicula, sometimes of a calcareous, at others of a
siliceous, nature.” Thus, a frame of siliceous matter being formed by
the living animal, a deposition of the same substance is continued
after death.

Sea-urchins and star-fish, and numerous fossil shells, are found in
these beds, which, however, differ materially from the remains of the
same animals found in the earlier formations. A vast number of new
species and genera of fish are also discovered in the chalk.

Nearly all the animals and plants which existed up to this period are
now extinct, although they have some imperfect representatives at the
present day.

The uppermost group, which has been called the supercretaceous or
tertiary formation, appears in our island to have been formed during
four great eras, as we find fresh-water deposits alternating with
marine ones. The term _eocene_, which is the first or oldest deposit;
_miocene_, which is the second; _pliocene_, which is the third; and the
_newer pliocene_,--which is the fourth and last, have been applied to
these formations, the names referring to the respective proportions of
existing species found among their fossil shells.[242]

All these formations show distinct evidence of their having been
deposited from still or slowly-flowing deep waters. Thus the eocene
appears in the Paris basin,--formed clearly at an estuary, in which
are mingled some interesting fresh-water deposits;--in the lacustrine
formations in Auvergne; also at Aix; and in the north of Italy. It
appears probable that, in the formations generally termed eocene, both
fresh-water and marine deposits have been confounded, and several
formations of widely-different eras regarded as the result of one. We
have not yet been furnished with any distinct and clear evidence to
show that the deposits of the Paris basin, and those of Auvergne,
are of the same age. At all events, it is sufficient for our present
purpose to know that they are the result of actions which are now as
general as they were when the plastic clay of Paris, and its sulphate
of lime, or the London clay, were slowly deposited.

As a general conclusion, we may decide that, at the eocene period,
existing continents were the sites of vast lakes, rivers, and
estuaries, and were inhabited by quadrupeds, which lived upon
their thickly-wooded margins. Many remains, allied to those of the
hippopotamus, have been found in the subsidences of this period.

Examples of the miocene or middle tertiary era are to be found in
Western France, over the whole of the great valley of Switzerland, and
the valley of the Danube. In these deposits we find the bones of the
rhinoceros, elephant, hippopotamus, and the dinotherium, an extinct
animal, possessing many very distinguishing features.[243]

The pliocene period has been termed the age of elephants, and is most
remarkable for the great mastodons and gigantic elks, with other
animals not very unlike those which are contemporaneous with man.

In the superficial layers of the earth, the diluvium, alluvium, peat
and vegetable soil, we have a continuation of the history of the
mutations of our globe and of its inhabitants, which has been here so
briefly sketched. They bring us up to the period when man appeared in
the world, since whose creation it is evident no very extensive change
has been produced upon the surface. We have viewed the phenomena of
each great epoch, marked as they are by new creations of organized
beings, and it would appear as if, through the whole series, from
the primary rocks up to the modern alluvial deposits, a progressive
improvement of the earth’s surface had been effected, to fit it at last
for the abode of the human race.

Thus have we preserved for us, in a natural manner, evidences which, if
we read them aright, must convince us that the laws by which creation
has ever been regulated are as constant and unvarying as the Eternal
mind by which they are decreed. Our earth, we find, by the records
preserved in the foundation-stones of her mountains, has existed
through countless ages, and through them all exhibited the same active
energies that prevail at the present moment. By precisely similar
influences to those now in operation, have rocks been formed, which,
under like agencies, have been covered with vegetation, and sported
over by, to us, strange varieties of animal life. Every plant that
has grown upon the earliest rocks which presented their faces to the
life-giving sun, has had its influence on the subsequent changes of our
planet. Each trilobite, each saurian, and every one of the mammalia
which exist in the fossil state, have been small laboratories in which
the great work of eternal change has been carried forward, and, under
the compulsion of the strong laws of creation, they have been made
ministers to the great end of forming a world which might be fitting
for the presence of a creature endued with a spark taken from the
celestial flame of intellectual life.

For a few moments we will return to a consideration of the operations
at present exhibiting their phenomena, and examine what bearing they
have upon our knowledge of geological formations.

During periods of immense, but unknown, duration, the ocean and the dry
land are seen to have changed their places. Enormous deposits, formed
at the bottom of the sea, are lifted by some mechanical, probably
volcanic, force, above the waters, and the land, like the ocean
surrounding it, teems with life. This state of things lasts for ages;
but the time arrives when the ocean again floods the land, and a new
state of things, over a particular district, has a beginning.

It must not be imagined that the changes which we have spoken of, as if
they were the result of slow decay and gradual deposit, were effected
without occasional violent convulsions. Many of the strata which
were evidently deposited at the bottom of the sea, and, of course,
as horizontal beds, are now found nearly vertical. We have evidence
of strata of immense thickness having been subjected to forces that
have twisted and contorted them in a most remarkable manner. Masses of
solid rock, many thousand feet deep, are frequently bent and fractured
throughout their whole extent. Mountains have been upheaved by internal
force, and immense districts have suddenly sunk far below their usual
level. By the expansive force due to that temperature which must be
required to melt basaltic and trap rocks, the whole of the superficial
crust of a country has been heaved to a great height, immense fissures
have been formed by the breaking of the mass, and the melted matter has
been forced through the opening, and overflowed extensive districts, or
volcanoes have been formed, and wide areas have been buried under the
ashes ejected from them. With the cause of these convulsions we are at
present unacquainted.

We have evidence of the extent to which these forces may be exerted, in
the catastrophes which have occurred within historical times, and which
have happened even in our own day. Herculaneum and Pompeii, buried
under the lava and ashes of Vesuvius, in an hour when the inhabitants
of these cities were unprepared for such a fearful visitation,--the
frightful earthquakes which have, from time to time, occurred in South
America--are evidences of the existence of hidden forces which shake
the firm-set earth. Similar ravaging catastrophes may have often
occurred, and, involving cataclysms, swept the surface to produce the
changes we detect over every part of the earth, compared with which
the earthquakes and floods of history are but trivial things. Evidence
has been adduced, to show that the mountains of the Old World may
have approached in height the highest of the Andes or Himalayas, and
these have not been destroyed by any sudden effect, but by the slow
disintegrating action of the elements.[244] All these phenomena are
now in progress: the winds and the rains wear the faces of the exposed
rock; their _débris_, mixed with decayed vegetable and animal matter,
are washed off from the surface, and borne away by the rivers, to be
deposited in the seas. Thus it is that the great delta of the Ganges
is formed, and that a continual increase of matter is going on at the
mouths of rivers. The Amazon, the Mississippi, and other great rivers,
bear into the ocean, daily, thousands of tons of matter from the
surface of the earth.[245] This is, of course, deposited at the bottom
of the sea, and it must, in the process of time, alter the relative
levels of the ocean and the land. Islands have been lifted by volcanic
power from the bottom of the sea, and many districts in South America
have been depressed by the same causes.

Changes as extensive have been, in all probability, effected by forces
“equally or more powerful, but acting with less irregularity, and so
distributed over time as to produce none of those interregnums of
chaotic anarchy which we are apt to think (perhaps erroneously) great
disfigurements of an order so beautiful and harmonious as that of
nature.”[246] These forces are, without doubt, even now in action.

Had it not been for these convulsive disturbances of the surface,
the earth would have presented an almost uniform plain, and it would
have been ill-adapted for the abode of man. The hills raised by the
disturbances of nature, and the valleys worn by the storms of ages,
minister especially to his wants, and afford him the means of enjoyment
which he could not possess had the surface been otherwise formed. The
“iced mountain tops,” condensing the clouds which pass over them, send
down healthful streams to the valleys, and supply the springs of the
earth, thus securing the fertility and salubrity of the distant plains.
The severities of climate are mitigated by these conditions, and both
the people of the tropics and those dwelling near the poles are equally
benefited by them.

Gravitation, cohesion, motion, chemical force, heat, and electricity,
must, from that hypothetical time when the earth floated a cloud of
nebulous vapour, in a state of gradual condensation up to the present
moment, have been exercising their powers, and regulating the mutations
of matter.

When the dry land was beneath the waters, and when darkness was upon
the face of the deep, the same great operations as those which are
now in progress in the depths of the Atlantic, or in the still waters
of our inland lakes, were in full activity. At length the dry land
appears; and--mystery of mysteries--it soon becomes teeming with life
in all the forms of vegetable and animal beauty, under the aspect of
the beams of a glorious sun.

Geology teaches us to regard our position upon the earth as one far
in advance of all former creations. It bids us look back through
the enormous vista of time, and see, shining still in the remotest
distance, the light which exposes to our vision many of nature’s holy
wonders. The elements which now make up this strangely beautiful fabric
of muscle, nerves, and bone, have passed through many ordeals, ere yet
it became fashioned to hold the human soul. No grain of matter has been
added to the planet, since it was weighed in a balance, and poised with
other worlds. No grain of matter can be removed from it. But in virtue
of those forces which seem to originate in the sun, “the soul of the
great earth,” a succession of new forms has been produced, as the old
things have passed away.

Under the forces we have been considering, acting as so many contending
armies, matter passes from one condition to another, and what is now
a living and a breathing creature, or a delicate and sweetly-scented
flower, has been a portion of the amorphous mass which once lay in the
darkness of the deep ocean, and it will again, in the progress of time,
pass into that condition where no evidences of organization can be
found,--again, perhaps, to arise clothed with more exalted powers than
even man enjoys.

When man places himself in contrast with the Intelligences beyond him,
he feels his weakness; and the extent of power which he can discover at
work, guided by a mysterious law, is such, that he is dwarfed by its
immensity. But looking on the past, surveying the progress of matter
through the inorganic forms up to the higher organizations, until at
length man stands revealed as the chief figure in the foreground of the
picture, the monarch of a world on which such elaborate care has been
bestowed, and the absolute ruler of all things around him, he rises
like a giant in the conscious strength of his far-searching mind. That
so great, so noble a being, should suffer himself to be degraded by the
sensualities of life to a level with the creeping things, upon which he
has the power to tread, is a lamentable spectacle, over which angels
must weep.

The curious connection between the superstitions of races, the
traditionary tales of remote tribes, and the developments of the truths
of science, are often of a very marked character, and they cannot but
be regarded as instructive. In the wonders of “olden time” fiction has
ever delighted; and a thousand pictures have been produced of a period
when beings lived and breathed upon the earth which have no existence
now.

Hydras, harpies, and sea-monsters, figure in the myths of antiquity.
In the mythology of the northern races of Europe we have fiery flying
dragons, and Poetry has placed these as the guardians of the “hoarded
spirit” and protectors of the enchanted gold.

Through the whole of the romance period of European literature,
nothing figures but serpents, “white and red,” toiling and fighting
underground,--thus producing earthquakes, as in the story of Merlin
and the building of Stonehenge. Flying monsters, griffins and others,
which now live only in the meaningless embellishments of heraldry,
appear to have been conceived by the earlier races of men as the
representatives of power. Curious is it, too, to find the same class
of ideas prevailing in the East. The monster dragons of the Chinese,
blazoned on their standards and ornamenting their temples;--the
Buddaical superstition that the world is supported on a vast elephant,
which stands on the back of a tortoise, which again rests on a serpent,
whose movements produce earthquakes and violent convulsions;--the rude
decorations also of the temples of the Aztecs, which have been so
recently restored to our knowledge by the adventurous travellers of
Central America,--all give expression to the same mythological idea.

Do not these indicate a faint and shadowy knowledge of a previous
state of organic existence? The process of communion between man of
the present, and the creations of a former world, we know not; it is
mysterious, and for ever lost to us. But even the most ignorant and
uncultivated races of mankind have figured for themselves the images
of creatures which, whilst they do really bear some resemblance to
things which have for ever passed away, do not, in the remotest degree,
partake of any of the peculiarities of existing creations.

The ichthyosaurus, and the plesiosaurus, and the pterodactylus, are
preserved in the rude images of harpies, of dragons, and of griffins;
and, although the idea of an elephant standing on the back of a
tortoise was often laughed at as an absurdity, Captain Cautley and
Dr. Falconer at length discovered in the hills of Asia the remains of
a tortoise in a fossil state of such a size that an elephant could
easily have performed the feat.[247]

Of the ammonites, we have more exact evidence; they were observed by
our forefathers, and called by them snake-stones. According to the
legends of Catholic saints they were considered as possessing a sacred
character:--

    “Of these and snakes, each one
    Was changed into a coil of stone
    When holy Hilda prayed.”

And in addition to this petrifying process, one of decapitation is said
to have been effected; hence the reason why these _snake-stones_ have
no heads.

We also find, in the northern districts of our island, that the name of
“St. Cuthbert’s beads” is applied to the fossil remains of encrinites.

Thus we learn that, to a great extent, fiction is dependent upon
truth for its creations; and we see that when we come to investigate
any wide-spread popular superstition, although much distorted by the
medium of error through which it has passed, it is frequently founded
upon some fragmentary truth. There are floating in the minds of men
certain ideas which are not the result of any associations drawn from
things around; we reckon them amongst the mysteries of our being. May
they not be the truths of a former world, of which we receive the dim
outshadowing in the present, like the faint lights of a distant Pharos,
seen through the mists of the wide ocean?

Man treads upon the wreck of antiquity. In times which are so long
past, that the years between them cannot be numbered by the aids of
our science, geology teaches us that forms of life existed perfectly
fitted for the conditions of the period. These performed their offices
in the great work; they passed away, and others succeeded to carry
on the process of building a world for man. The past preaches to
the present, and from its marvellous discourses we venture to infer
something of the yet unveiled future. The forces which have worked
still labour: the phenomena which they have produced will be repeated.

    Ages on ages slowly pass away,
    And nature marks their progress by decay.
    The plant which decks the mountain with its bloom,
    Finds in the earth, ere long, a damp dark tomb:
    And man, earth’s monarch, howe’er great and brave--
    Toils on--to find at last a silent grave.
    The chosen labours of his teeming mind
    Fade by the light, and crumble ’neath the wind;
    And e’en the hills, whose tops appear to shroud
    Their granite peaks deep in the vapoury cloud,
    Worn by tempests--wasted by the rains,
    Sink slowly down to fill wide ocean’s plains.
    The ocean’s breast new lands again display,
    And life and beauty drink the light of day:
    The powers which work at great creation’s wheel,
    Will from the wrecks of matter still reveal
    New forms of wondrous beauty--which will rise
    Pure as the flame of love’s young sacrifice,
    Beaming with all the pristine hues of youth,
    Robed by the day, and crowned by holy truth.


FOOTNOTES:

[231] _Preliminary Discourse_; Sir J. F. W. Herschel. Lardner’s Cabinet
Cyclopædia.

[232] _Geological Researches_; by Sir Henry De la Beche, C.B.
(_Degradation of Mountains_, p. 167.) _Geological Manual_, p. 184.
_Principles of Geology_; by Sir Charles Lyell, 7th Edition, p. 150,
686. _On the Denudation of South Wales, and the adjacent countries of
England_; by Professor Andrew Ramsay; Memoirs of the Geological Survey
and Museum of Practical Geology, vol. i. p. 297.

[233] Fownes, _On the Existence of Phosphoric Acid in Rocks of Igneous
Origin_; Phil. Trans. 1844, p. 53. Nesbitt, _Quarterly Journal of the
Chemical Society_.

[234] _On the Vegetation of the Carboniferous Period as compared
with that of the present day; On some peculiarities in the structure
of Stigmaria; Remarks on the Structure and Affinities of some
Lepidostrobi_: by Dr. Hooker; Memoirs of the Geological Survey, &c.,
vol. ii. pp. 387, 431, 440.

[235] See Owen, Quarterly Journal of the Geological Society, No. 6,
p. 96. Dr. Buckland, Geological Transactions, vol. iii. p. 220. _The
Wonders of Geology_: by Dr. Mantell, vol. ii. p. 493.

[236] _Report on British Fossil Mammalia_: by Richard Owen, Esq.,
F.R.S.; British Association Reports, vols. xi. xii.

[237] _Notice on the Iguanodon, a newly discovered fossil reptile from
the sandstone of Tilgate Forest, in Sussex_: by Gideon Mantell, Esq,
F.R.S., &c.; Philosophical Transactions, vol. cxv. p. 179. _On the
Structure of Teeth, &c._; by Professor Owen.

[238] Dr. Mantell, _Wonders of Geology_. _Geology of the South-east of
England._

[239] _Geological Researches_; _Geological Manual_; by Sir Henry Thos.
De la Beche, C.B., &c.

[240] Ibid.

[241] _Experimental Researches on the production of Silicon from
Paracyanogen_: by Samuel Brown, M.D.; Transactions of the Royal Society
of Edinburgh, vol. xv. p. 229. _Experiments on the alleged conversion
of Carbon into Silicon_: by R. H. Brett, Ph.D., and J. Denham Smith,
Esq.; Philosophical Magazine, vol. xix. p. 295, New Series. See also
Dr. Brown’s reply to the above, ibid, p. 388.

[242] _Geology, Introductory, Descriptive, and Practical_: by Prof.
Ansted, vol. ii. p. 22.

[243] _The Wonders of Geology_: by Dr. Mantell, vol. i. p. 162.
_Bridgewater Treatise_: by Dr. Buckland. Dr. J. J. Kemp, and Dr. A.
V. Klipstein, _On the Dinotherium_; Darmstadt, 1836. Cuvier and De
Blainville have also carefully described the fossil remains of this
animal.

[244] See Professor Ramsay’s memoir _On Denudation_: Memoirs of the
Geological Survey of Great Britain.

[245] “The distances to which river water, more or less charged with
detritus, would flow over sea-water, will depend upon a variety
of obvious circumstances. Captain Sabine found discoloured water,
supposed to be that of the Amazons, three hundred miles distant in
the ocean from the embouchure of that river. It was about 126 feet
deep. Its specific gravity was = 1·0204, and the specific gravity of
the sea-water = 1·0262. This appears to be the greatest distance from
land at which river water has been detected on the surface of the
ocean. If rivers, containing mechanically suspended detritus, flowed
over sea-water in lines which, in general terms, might be called
straight, the deposit of transported matter which they carried out
would also be in straight lines. If, however, they be turned aside
by an ocean current, as was the case with that observed by Captain
Sabine, the detritus would be thrown, and cover an area corresponding
in a great degree with the sweep which the river has been compelled
to make out of the course, that its impulse, when discharged from its
embouchure, might lead it to take: supposing the velocity with which
this river-water was moving has been correctly estimated at about
three miles per hour, it is not a little curious to consider that the
agitation and resistance of its particles should be sufficient to keep
finely comminuted solid matter mechanically suspended, so that it
would not be disposed freely to part with it, except at its junction
with the sea-water over which it flows, and where, from friction, it
is sufficiently retarded. So that a river, if it can preserve a given
amount of velocity flowing over the sea, may deposit no very large
amount of mechanically suspended detritus in its course from the
embouchure, where it is ultimately stopped. Still, however, though the
deposit may not be so abundant as at first sight would appear probable,
the constant accumulation of matter, however inconsiderable at any
given time, must produce an appreciable effect during the lapse of
ages.”--Sir Henry De la Beche’s _Geological Researches_, p. 72.

[246] Sir J. F. W. Herschel: _Preliminary Treatise_.

[247] _Fauna Antiqua Sivalensis. Being the Fossil Zoology of the
Sewalik Hills in the North of India_: by Hugh Falconer and Proby T.
Cautley. 1844.




CHAPTER XIV.

PHENOMENA OF VEGETABLE LIFE.

  Psychology of Flowers--Progress of Matter towards
    Organization--Vital Force--Spontaneous Generation--The Vegetable
    Cell--Simplest Development of Organization--The Crystal and
    the Cell--Primitive Germ--Progress of Vegetation--Influence
    of Light--Morphology--Germination--Production of Woody
    Fibre--Leaves--Chlorophylle--Decomposition of Carbonic
    Acid--Influence of Light, Heat, and Actinism on the Phenomena of
    Vegetable Life--Flowers and Fruits--Etiolation--Changes in the
    Sun’s Rays with the Seasons--Distribution of Plants--Electrical and
    Combined Physical Powers


The variety of beautiful forms which cover the surface of this sphere,
serve, beyond the physical purposes to which we have already alluded,
to influence the mind, and give character to the inhabitants of every
locality. There are men who appear to be dead to the mild influences
of flowers; but these sweet blossoms--the stars of our earth--exert a
power as diffusive as their pervading odours.

The poet tells us of a man to whom

    The primrose on the river’s brim
    A yellow primrose was to him,
    And it was nothing more.

But it was something more. He, perhaps, attended not to the eloquent
teaching of its pure, pale leaves: he might not have been conscious
of the mysterious singing of that lowly flower: he might, perchance,
have crushed it beneath his rude foot rather than quaff the draught of
wisdom which it secreted in its cell; but the flower still ministered
to that mere sensualist, and in its strange, tongueless manner,
reproved his passions, and kept him “a wiser and a better man,“ than if
it had pleased God to have left the world without the lovely primrose.

The psychology of flowers has found many students--than whom not one
read them more deeply than that mild spirit who sang of the Sensitive
Plant, and in wondrous music foreshadowed his own melancholy fate.[248]
That martyr to sensibility, Keats, who longed to feel the flowers
growing above him, drew the strong inspiration of his volant muse from
those delicate creations which exhibit the passage of inorganic matter
into life; and other poets will have their sensibilities awakened by
the æsthetics of flowers, and find a mirror of truth in the crystal
dew-drop which clings so lovingly to the purple violet, and draws fresh
beauties from its  petals.

If we examine carefully all the conditions of matter which we have
made the subject of our studies, we cannot but perceive how gradual
is the progress of the involved action of the physical forces, as we
advance from the molecule--the mere particle of matter--up to the
organic combination. At first we detect only the action of cohesion in
forming the rude mass; then we have the influence of the crystallogenic
powers giving a remarkable regularity to bodies; we next discover the
influences of heat and electrical force in determining condition, and
of chemical action as controlled by them. Yet, still we have a body
without organization. Light exerts its mysterious powers, and the same
elements assume an organized form; and, in addition to the recognized
agencies, we dimly perceive others on which vitality evidently
depends. These empyreal influences become more and more complicated
to us: ascending in the scale, they rise beyond our science; and, at
length, we find them guiding the power of intelligence, while instinct
and reason are exhibited in immediate dependence upon them.

Let it not be imagined that this view has any tendency to materialism.
The vital energy is regarded as a spiritualization, and reason as a
divine emanation; but they are connected with materialities, on which
they act, and by which they are themselves controlled. The organic
combinations, and the physical powers by which these unions of matter
are effected and retained, have a direct action over that ethereality
which is life, and the powers of life again control these more material
forces. The spirit, in whatever state, when connected with matter, is,
like Prometheus chained to his rock, in a constant struggle to escape
from its shackles, and assert the full power of its divine strength.

We have seen variety enough in the substances which make up the
inorganic part of creation; but infinitely more varied are the forms
of organization. In the vegetable world which is immediately around
us, from the green slime of our marshes to the lustrous flowers of our
gardens and the lordly trees of our forests, what an extraordinary
diversity of form is apparent! From the infusoria of an hour, to the
gigantic elephant roaming in his greatness in the forests of Siam--the
noble lion of the caves of Senegal--the mighty condor of the Andes--and
onward to man, the monarch of them all, how vast are the differences,
and yet how complete are they in their respective conditions! In the
creation we have examined, we have had conclusive evidence, that from
the combination of _atoms_ every peculiar form has been produced. In
the creation we are about to examine, we shall discover that all the
immense diversity of form, of colour, and condition which is spread
over the world in the vegetable and animal kingdoms, results from the
combination of _cells_. The atom of inorganic nature becomes a cell in
organic creation. This cell must be regarded as the compound radical of
the chemist, and by decomposing it, we destroy the essential element of
organization.

With the mysterious process by which the atom is converted into a
cell, or a compound radical, we are unacquainted; but we must regard
the cell as the organic atom. It is in vain that the chemist or the
physiologist attempts to examine this change of the inorganic elements
to an organized state; it is one of the mysteries of creation, which is
to be, in all probability, hid from our eyes, until this “mortal coil”
is shaken off, and we enjoy the full powers of that intelligence which
we are promised we shall enjoy in an immortal state.

Again and again has the attention of men been attracted to the
_generatio æquivoca_; they have sometimes thought they have discovered
a _generatio primitiva_ or _spontanea_; but a more careful examination
of these organisms has shown that an embryo existed--a real germination
has taken place.

Count Rumford[249] stated that threads of silk and wool had the power
of decomposing carbonic acid in water in the sunshine; and hence some
have referred organization to a mere chemical change produced by
luminous excitation; and we have heard of animal life resulting from
pounded siliceous matter. All such statements must be regarded as
evidences of imperfect investigation.

Dr. Carus, alluding to the experiments of Gruithuisen, Priestley, and
Ingenhousz,[250] says:--“These show, more than any other experiments,
that, in the purest water, under the influence of air, light, and heat,
beings are formed, which, oscillating as it were between the animal
and the plant, exhibit the primitive germs of both kingdoms.”[251]
Treviranus[252] repeated, and appeared to confirm these results; but in
these experiments we have no evidence that the germ did not previously
exist in the spring-water which was employed.

Some have regarded the cell as a crystal; they see the crystal forming,
by the accumulation of atoms, into a fixed form, under the influence
of an “inner life;” and, advancing but a step, they regard the cell as
the result of an increased exercise of the physical influences.[253]
We have referred crystalline form to certain magnetic conditions; and
it is evident that the atomic cell is influenced by similar forces;
but if we place a crystal in its natural fluid, though it increases in
size, it never alters in form: whereas, if we examine a cell in its
natural position, it gives indications of motion, it produces other
cells, and we have a development of organs which are in no respect
the same in form as the original. From a vesicle floating invisible
to the unaided human sense in its womb of fluid, is produced a plant
possessing strange powers, or an animal gifted with volition. The idea,
that two kinds of polarity--light on one side, and gravitation on the
other--produce the two peculiar developments of roots and branches, can
only be regarded as one of those fanciful analogies which prove more
imagination than philosophy.[254]

The conditions are, however, most curious; they deserve very attentive
study; but in examining the phenomena, the safest course is to allow
the effects as they arise to interpret to us, and not admit the love
of hypothesis to lead us into bewildering analogies; or uncertain
phenomena to betray us to hasty inferences. It is of this evil that
Bacon speaks, in his “Advancement of Learning.” He says:--

“The root of this error, as of all others, is this, that men, in
their contemplations of nature, are accustomed to make too timely a
departure, and too remote a recess from experience and particulars, and
have yielded and resigned themselves over to the fumes of their own
fancies and popular argumentations.”

Without venturing, therefore, to speculate on the origin of the
primitive cell, or unit of organic life, which involves the problem
of the metamorphosis of a rude mass--the primitive transformation
of the rudimentary atoms into organic form,--we must admit that the
highly organized plant or animal is but an aggregation of cells; their
arrangement being dependent upon certain properties peculiar to them,
and the exercise of forces such as we have been studying,--all of which
appear to act externally to the plant or animal itself.

Experiments have been brought forward, in which it appeared that, after
all organization which could by any possibility have existed, had
been destroyed by the action of fire, solutions of flint and metallic
salts, have, under the influence of electric currents, exhibited
signs of organic formations, and that, indeed, insects--a species
of acari--have been developed in them. The experiments were said to
have been made with care, and many precautions taken to shut out
all chances of any error, but not all the precautions required in a
matter of such exceeding delicacy; and we are bound not to receive the
evidence afforded as the true expression of a fact without much further
investigation. All experience,--setting aside the experiment named,--is
against the supposition that pounded or dissolved flint could by any
artificial means be awakened into life. Ova may have been conveyed
into the vessels which contained the solutions under experiment; and
in due time, although possibly quickened by electric excitation, the
animals--the most common of insects--came into existence.[255]

The rapid growth of confervæ upon water has often been brought forward
as evidence of a spontaneous generation, or the conversion of inorganic
elements into organic forms; but it has been most satisfactorily proved
that the germ must be present, otherwise no evidence of anything
like organization will be developed. All the conditions required for
the production of vegetable life appear to show, that it is quite
impossible for any kind of plant, even the very lowest in the scale, to
be formed in any other way than from an embryo in which are contained
the elements necessary for it, and the arrangements required for the
various processes which are connected with its vitality.

The earth is now covered with vegetable life, but there must have
existed a time when “darkness was upon the face of the deep,” and
organization had not yet commenced tracing its lovely net-work of cells
upon the bare surface of the ocean-buried rock. At length the mystery
of organic creation began: into this science dares not penetrate, but
it is privileged to begin its search a little beyond this point, and
we are enabled to trace the progress of organic development through a
chain of interesting results which are constantly recurring.

If we take some water, rising from a subterranean spring, and expose
it to sunshine, we shall see, after a few days, a curious formation
of bubbles, and the gradual accumulation of green matter. At first we
cannot detect any marks of organization--it appears a slimy cloud of
an irregular and undetermined form. It slowly aggregates, and forms a
sort of mat over the surface, which at the same time assumes a darker
green colour. Careful examination will now show the original corpuscles
involved in a net-work formed by slender threads, which are tubes of
circulation, and may be traced from small points which we must regard
as the compound atom, the vegetable unit. We must not forget, here,
that we have to deal with four chemical elements,--oxygen, hydrogen,
carbon, and nitrogen, which compose the world of organized forms, and
that the water affords us the two first as its constituents, gives us
carbon in the form of carbonic acid dissolved in it, and that nitrogen
is in the air surrounding it, and frequently mixed with it also.

Under the influence of sunshine, we have now seen these elements
uniting into a mysterious bond, and the result is the formation of a
cellular tissue, which possesses many of the functions of the noblest
specimens of vegetable growth. But let us examine the progress. The
bare surface of a rock rises above the waters covered over with this
green slime, a mere veil of delicate net-work, which, drying off,
leaves no perceptible trace behind it; but the basis of a mighty growth
is there, and under solar influence, in the process of time, other
changes occur.

After a period, if we examine the rock, we shall find upon its face
little  cups or lines with small hard discs. These, at first
sight, would not be taken for plants, but on close examination they
will be found to be lichens. These minute vegetables shed their seed
and die, and from their own remains a more numerous crop springs into
life. After a few of these changes, a sufficient depth of soil is
formed, upon which mosses begin to develope themselves, and give to
the stone a second time a faint tint of green, a mere film still, but
indicating the presence of a beautiful class of plants, which, under
the microscope, exhibit in their leaves and flowers many points of
singular elegance. These mosses, like the lichens, decaying, increase
the film of soil, and others of a larger growth supply their places,
and run themselves the same round of growth and decay. By and by,
funguses of various kinds mingle their little globes and umbrella-like
forms. Season after season plants, perish and add to the soil, which is
at the same time increased in depth by the disintegration of the rock
over which it is laid, the cohesion of particles being broken up by the
operations of vegetable life. The minute seeds of the ferns floating on
the breeze, now find a sufficient depth of earth for germination, and
their beautiful fronds, eventually, wave in loveliness to the passing
winds.

Vegetable forms of a higher and a higher order gradually succeed each
other, each series perishing in due season, and giving to the soil
additional elements for the growth of plants of their own species or
those of others. Flowering herbs find a genial home on the once bare
rock; and the primrose pale, the purple foxglove, or the gaudy poppy,
open their flowers to the joy of light. The shrub, with its hardy roots
interlaced through the soil, and binding the very stones, grows rich
in its bright greenery. Eventually the tree springs from the soil,
and where once the tempest beat on the bare cold rock, is now the
lordly and branching monarch of the forest, with its thousand leaves,
affording shelter from the storm for bird and beast.

Such are the conditions which prevail throughout nature in the progress
of vegetable growth; the green matter gathering on a pond, the mildew
accumulating on a shaded wall, being the commencement of a process
which is to end in the development of the giant trees of the forest,
and the beautifully tinted flower of nature’s most chosen spot.

We must now consider closely the phenomena connected with the growth of
an individual plant, which will illustrate the operation of physical
influences throughout the vegetable world. The process by which the
embryo, secured in the seed, is developed, is our first inquiry.

A seed is a highly carbonized body, consisting of integuments and
embryo: between these, in most seeds, lies a substance called the
_albumen_, or _perisperm_. The embryo contains the elements of the
future plant--the cotyledons, the plumule, and the radicle; the
former developing into stalk and leaves, the latter into roots. This
embryo hides the living principle, for the development of which it
is necessary that the starch and gluten undergo a chemical change,
and that an elevation of temperature is produced. The vital power
is dormant--it sleeps--in the seed until the proper conditions are
produced. It has been proved, that the powers of maintaining life
in the seed are very great; excessive cold, sufficiently intense to
freeze mercury, will not kill seed, and they resist a comparatively
high temperature. It is probable that heat only destroys seeds by
drying them too completely. The temperature at which seeds germinate is
exceedingly varied,--those belonging to our own clime will germinate
when the thermometer rises above 40° F., but the seeds of tropical
plants demand that a temperature of from 70° to 84°, or even to 90°,
be steadily applied to them. In some cases it has been found that
even boiling the seeds has been advantageous to the future process of
germination in the soil. But let us take the seed of some ordinary
plant, and trace its progress.

An apparently dead grain is placed in the soil. If the temperature is a
few degrees above the freezing point, and the soil holds a due quantity
of water, the integument of the seed imbibes moisture and swells; the
tissue is softened, and the first effort of vital force begins. The
seed has now the power of decomposing water, the oxygen combines with
some of the carbon of the seed, and is expelled as carbonic acid.
Saussure’s experiments prove this. The air above the soil in which
a horse-bean was placed to germinate, gave, before the experiment,
nitrogen 210·26, and oxygen 56·29, and after germination, nitrogen
209·41, oxygen 44·38, and carbonic acid 11·27. This part of the process
is but little removed from the merely chemical changes which we have
already considered. We find the starch of the seed changed into gum and
sugar, which affords nutritive food for the developing embryo. The seed
now lengthens downwards by the radicle, and upwards by the cotyledons,
which, as they rise above the earth, acquire a green colour. Here the
first stage of vegetable life ends, the chemically exciting process is
at an end, and a new stimulus is required to continue in full activity
the vital powers. Carbonic acid is no longer given off.

The cotyledons, which are two opposite roundish leaves, act as the
lungs; by them carbonic acid taken from the atmosphere is absorbed
and carried by a circulating process, now in full activity, through
the young plant. The carbonic acid, a compound of carbon and oxygen,
is decomposed; it is deprived of its carbon, which is retained by the
plant, and oxygen is exhaled. The plant at this period is little more
than an arrangement of cellular tissue, a very slight development
of vascular and fibrous tissue appearing as a cylinder lying in the
centre of the sheath. At this point, however, we begin more distinctly
to trace the operations of the new power; the impulses of life are
strikingly evident.

The young root is now lengthening, and absorbing from the moisture in
the soil, which always contains some soluble salts, a portion of its
nutriment, which is impelled upwards by a force--probably capillary
attraction and endosmose action combined--to the point from which the
plumule springs. Capillary force raises the fluids through the tubes
in the stalk, and conveys them to the veins in the leaves, while
the endosmose force diffuses them through the vegetable tissues.
The plumule first ascends as a little twig, and, at the same time,
by exerting a more energetic action on the carbonic acid than the
cotyledons have done, the carbon retained by them being only so much
as is necessary to form chlorophylle, or the green colouring matter of
leaves, some wood is deposited in the centre of the radicle. From this
time the process of lignification goes on through all the fabric,--the
increase, and indeed the life, of the plant depending upon the
development of a true leaf from the plumule.

It must not be imagined that the process consists, in the first place,
of a mere oxidation of the carbon in the seed,--a slow combustion by
which the spark of life is to be kindled;--the hydrogen of the water
plays an important part, and, combining also with the carbon, forms
necessary compounds, and by a secondary process gives rise again to
water by combination with oxygen in the cells of the germinating grain.
Nor must we regard the second class of phenomena as mere mechanical
processes for decomposing carbonic acid, but the result of the combined
influences of all the physical powers and life superadded.

This elongating little twig, the plumule, at length unfolds itself, and
the branch is metamorphosed into a leaf. The leaf aërates the sap it
receives, effects the decomposition of the carbonic acid, the water,
and in all probability the ammonia which it derives from the air,
and thus returns to the pores, which communicate with the pneumatic
arrangements of the plant, the necessary secretions for the formation
of bark, wood, and the various proximate principles which it contains.

After the first formation of a leaf, others successively appear, all
constructed alike, and performing similar functions. The leaf is the
principal organ to the tree; and, indeed, Linnæus divined, and Goethe
demonstrated, the beautiful fact, that the tree was developed from this
curiously-formed organ.

“Keeping in view,” says the poet-philosopher, “the observations that
have been made, there will be no difficulty in discovering the leaf in
the seed-vessel, notwithstanding the variable structure of that part
and its peculiar combinations. Thus the pod is a leaf which is folded
up and grown together at its edges, and the capsules consist of several
leaves grown together, and the compound fruit is composed of several
leaves united round a common centre, their sides being opened so as to
form a communication between them, and their edges adhering together.
This is obvious from capsules which, when ripe, split asunder, at which
time each portion is a separate pod. It is also shown by different
species of one genus, in which modifications exist of the principle
on which their fruit is formed; for instance, the capsule of _nigella
orientalis_ consists of pods assembled round a centre, and partially
united; in _nigella damascena_ their union is complete.”[256]

Professor Lindley thus explains the same view:--“Every flower, with
its peduncle and bracteolæ, being the development of a flower-bud, and
flower-buds being altogether analogous to leaf-buds, it follows as a
corollary that every flower, with its peduncle and bracteolæ, is a
metamorphosed branch.

“And, further, the flowers being abortive branches, whatever the laws
are of the arrangement of branches with respect to each other, the same
will be the laws of the flowers with respect to each other.

“In consequence of a flower and its peduncle being a branch in a
particular state, the rudimentary or metamorphosed leaves which
constitute bracteæ, floral envelopes, and sexes, are subject to exactly
the same laws of arrangement as regularly-formed leaves.”[257]

The idea that the leaf is the principal organ of the plant, and that
from it all the other organs are probably developed, is worthy the
genius of the great German poet.

Every leaf, a mystery in itself, is an individual gifted with peculiar
powers; they congregate in families, and each one ministers to the
formation of the branch on

which it hangs, and to the main trunk of the tree of which it is a
member. The tree represents a world, every part exhibiting a mutual
dependence.

    “The one red leaf, the last of its clan,
    That dances as often as dance it can;
    Hanging so light and hanging so high,
    On the topmost twig that looks up at the sky,”

is influenced by, and influences, the lowest root which pierces
the humid soil. Like whispering voices, the trembling leaves sing
rejoicingly in the breeze and summer sunshine, and they tremble alike
with agony when the equinoctial gale rends them from the parent stalk.
The influences which pervade the whole, making up the sum of vital
force, are disturbed by every movement throughout the system; a wound
on a leaf is known to disturb the whole, and an injury inflicted on the
trunk interferes with the processes which are the functions of every
individual leaf.[258]

The consideration of the physical circumstances necessary to
germination and vegetable growth, brings us acquainted with many
remarkable facts. At a temperature below the freezing point, seeds will
not germinate; at the boiling point of water, a chemical change is
produced in the grain, and its power of germinating is destroyed. Heat,
therefore, is necessary to the development of the embryo, but its power
must only be exerted within certain prescribed limits: these limits are
only constant for the same class of seeds, they vary with almost every
plant. This is apparent to every one, in the different periods required
for germination by the seeds of dissimilar vegetables.

The seed is placed in the soil; shade is always--absolute darkness
sometimes--necessary for the success of the germinating process. We
have seen that the first operation of nature is purely a chemical one,
but this manifestation of affinity is due to an exertion of force,
which is directly dependent upon solar power. The seed is buried in the
soil, when the genial showers of spring, and the increasing temperature
of the earth, furnish the required conditions for this chemistry of
life, and the plant eventually springs into sunshine. Thus we obtain
evidence that even through some depth of soil the solar power, whatever
it may be, is efficient, and that under its excitement the first spring
of life, in the germ, is effected.

The cotyledons and the plumule being formed, the plant undergoes a
remarkable change. The seed, like an animal, absorbed oxygen and
exhaled carbonic acid; the first leaves secrete carbon from carbonic
acid inspired, and send forth, as useless to the plant, an excess of
oxygen gas.

This power of decomposing carbonic acid is a vital function which
belongs to the leaves and bark. It has been stated, on the authority
of Liebig, that during the night the plant acts only as a mere bundle
of fibres,--that it allows of the circulation of carbonic acid and
its evaporation, unchanged. In his eagerness to support his chemical
hypothesis of respiration, the able chemist neglected to inquire
if this was absolutely correct. The healthy plant never ceases to
decompose carbonic acid during one moment of its existence; but during
the night, when the excitement of light is removed, and the plant
reposes, its vital powers are at their minimum of action, and a much
less quantity is decomposed than when a stimulating sun, by the action
of its rays, is compelling the exertion of every vital function.

During this process, we have another example of natural organic
chemistry. The four inorganic elements of which the vegetable kingdom
is composed--oxygen, hydrogen, nitrogen, and carbon--are absorbed as
air or moisture by the leaves and through the roots, and the great
phenomenon of vegetable life is the conversion of these to an organic
condition. Sugar and gum are constantly produced, and from these, by
combination with atmospheric nitrogen, a proteine compound is formed,
which is an essential element in the progress of development.[259]

Plants growing in the light are beautifully green, the intensity of
colouring increasing with the brilliancy of the light. Those which are
grown in the dark are etiolated, their tissues are weak and succulent,
their leaves of a pale yellow. It is, therefore, evident that the
formation of this chlorophylle--as the green colouring matter of leaves
is called--results from some action determined by the sun’s rays.

Chlorophylle is a carbonaceous compound formed in the leaves, serving,
it would appear, many purposes in the process of assimilation. In the
dark the plant still requires carbon for its further development,
and growing slowly, it removes it from the leaves, decomposing the
chlorophylle, and supports its weak existence by preying on parts of
its own structure, until at length, this being exhausted, it actually
perishes of starvation.

Plants always turn towards the light: the guiding power we know not,
but the evidence of some impulsive or attracting force is strong; and
the purpose for which they are constituted to obey it, is proved to be
the dependence of vegetable existence upon luminous power.

Light is not, however, alone sufficient to perfect the plant: another
agent is required to aid in the production of flowers and fruits,
and this power is proved to be heat--and heat, perhaps, in some
peculiar condition. Having reached that point of development when
the reproductive functions are, by another change in the chemical
operations going on within the vegetable structure, to be called forth,
it has been found that the heat rays become in a remarkable manner
effective. It has also been observed that plants bend from the red,
or calorific rays, instead of towards them, as they are found to do
to every other ray of the spectrum. From this we may argue that the
influence of these rays is to check the vegetation, and thus to ensure
the perfection of the reproductive processes.

It has already been stated that we have the means of separating, to
a considerable extent, the three principles which we discover in the
sunbeam, from each other, by the use of absorbent media.

By a peculiar yellow glass we cut off the chemical principle of the
sunbeam, and admit the passage of the _luminous rays_ only--LIGHT.

By a cobalt blue glass we obstruct the _light_, but allow the chemical
agent to pass through freely, without, indeed, any loss--ACTINISM.

By a glass  deep blood-red by oxide of gold we obstruct
the chemical principle and much of the light, but such a medium is
perfectly transparent to HEAT.

Therefore, this gives us the means of experimenting with either of
these principles, and of examining the parts which they respectively
play in the work of organization.

Some seeds being placed in the soil, in every respect in their natural
conditions, duly supplied with moisture, and a uniform and proper
temperature maintained, we place above the soil the three media
above named, and allow one portion to be exposed to all the ordinary
influences of the solar rays.

The result will be, that the seeds under the blue glass will germinate
long before those which are exposed to the combined influences of the
sunshine: a few of the seeds will struggle into day under the red
glass, but the process of germination is entirely checked under the
yellow glass. Here we see that the chemical radiations have quickened
the chemical changes, and accelerated the process, under the red glass,
through which rays having some peculiar chemical action pass; the
germinating process, though checked, is not entirely stopped. Whereas,
it would appear that under the influences of light which has been
deprived of chemical power, this conversion of the starch into gum and
sugar, which appears to be necessary, is entirely prevented.

If the experiment is continued, it will be found that under the
blue glass the plants grow rapidly, but weakly; and that instead of
producing leaves and wood they consist chiefly of stalk, upon which
will be seen here and there some abortive attempts to form leaves.
When the process of germination has terminated, if the young plant is
brought under the yellow glass, it grows most healthfully, and forms an
abundance of wood, the leaves having an unusually dark green colour,
from the formation of a large quantity of chlorophylle. Plants do not,
however, produce flowers with readiness under this medium; but if, at
the proper period, they are brought under the red glass, the flowering
and fruiting processes are most effectively completed.[260]

These experiments, simple as they are, prove to us the importance of
light: the _luminous principle_ of the sunbeam is exciting the vital
powers of the plant to decompose carbonic acid and form wood; and the
calorific agent, possibly under those modifications which have already
been noticed as belonging to the parathermic rays, is essential to the
production of flower and fruit.

Observations, which have been extended over many years, prove that
with the seasons these solar powers are, relatively to each other,
subject to an interesting change. In the spring, the actinic or
chemical power prevails, and during this period its agency is required
for the vitalization of the germ. As the summer comes on, the actinic
rays diminish, and those of light increase. Perhaps it would be more
strictly correct to say that the luminous intensity being increased,
the chemical power was retarded; the former expression implies a
variation in quantity, which may not be correct. We see the necessity
for this, since luminous power is required for the secretion of
the carbon, with which the woody fibre is formed, and also for the
elaboration of the proximate principles of the plant. Autumn, the
season of fruit, is characterized by an increase of the heat rays, and
a diminution of the others: this change being necessary, as science now
teaches us, for the due production of flower and fruit.

The calorific rays of the solar beam, to which the autumnal phenomena
of vegetation appear particularly to belong, are of a peculiar
character. They have been called, the Parathermic rays, and exhibit a
curious compound nature. To these rays we may refer the ripening of
fruit and grain, and the browning of the leaf before its fall. May not
the rise of the sap in spring be traced to the excitement of either
light or actinism, and its recession, in the autumn, to that power
from which the plant is found to bend, and which appears to be their
modified form of heat?

There can be no doubt that the varieties of climate and the
peculiarities of countries, as it regards their animal and vegetable
productions, are dependent on the same causes. The distribution of
species has been referred by some to specific centres of creation
around which the plants and animals have spread, without reference to
physical conditions. Although centres of creation may be admitted,
these centres themselves have been determined by the physical
fitness of each centre to the conditions of the creation, and in
like manner the migration of tribes is solely due to these physical
forces we have been considering. In every zone we find that vegetable
organization is peculiarly fitted for the considerations by which it
is surrounded. Under the equator we have the spice-bearing trees, the
nutmeg, the clove, the cinnamon, and the pepper-tree; there we have
also the odoriferous sandal, the ebony, the banyan, and the teak: we
have frankincense, and myrrh, and other incense-bearing plants; the
coffee-tree, the tea-plant, and the tamarind.

A little further north we have the apricot, the citron, the peach,
and the walnut. In Spain, Sicily, and Italy, we have the orange and
lemon-tree blooming rich with perfume, and the pomegranate and the
myrtle growing wild upon the rocks. Beyond the Alps the vegetation
again changes; instead of the cypress, the chesnut, and the cork-tree,
which prevail to the south of them, we have the hardier oak, the beech,
and the elm. Still further north, we have the Scotch and spruce fir
and larch. On the northern shores of the Baltic, and in that line of
latitude, the hazel alone appears; and beyond this the hoary alder,
the sycamore, and the mountain ash. Within the Arctic circle we find
the mezereum, the water-lilies, and the globe-flowers; and, when the
weakness of the solar radiations becomes too great even for these,
the reindeer moss still lends an aspect of gladness to the otherwise
sterile soil.

The cultivation of vegetables depends on the temperature of the clime.
The vine flourishes where the mean annual temperature ranges between
50° and 73°, and it is only cultivated profitably within 30° S. and 50°
N. of the equator. To the same limits is confined the cultivation of
maize and of olives. Cotton is grown profitably up to latitude 46° in
the Old World, but only up to 40° in the New. We have evidence derived
from photographic phenomena, that the constitution of the solar rays
varies with the latitude. The effects of the sun’s rays in France and
England in producing chemical change are infinitely more decided than,
with far greater splendour of light, they are found to be in the lands
under or near the equator. Indeed, the remarks made on the variations
in the character of the sunbeam with the changing seasons, may apply
equally to the variations in latitude.

Fungals are among the lowest forms of vegetation, but in these we have
peculiarities which appear to link them with the animal kingdom. Marcet
found that mushrooms absorbed oxygen, and disengaged carbonic acid.
In all probability this is only a chemical phenomenon of a precisely
similar character to that which we know takes place with decaying
wood. In the conversion of wood into _humus_, oxygen is absorbed, and
combining with the carbon, it is evolved as carbonic acid. Of course we
have the peculiar condition of vitality to modify the effect, and we
have, too, in this class of plants, the existence of a larger quantity
of nitrogen than is found in any other vegetating substance.

These few sketches of remarkable phenomena connected with vegetation
are intended to show merely the operations of the physical powers of
the universe, so far as we know them, upon these particular forms
of organization. During the process of germination, electricity is,
according to Pouillet, evolved; and again, in ripening fruits, there
appears to be some evidence of electrical currents. Vegetables are,
however, in the growing state, such good conductors of electricity,
that it is not, according to the laws of this force, possible that
they should accumulate it; so that the luminous phenomena stated to
have been observed cannot be due to this agency. We know, however,
that under every condition of change, whether induced by chemical or
calorific action, electricity is set in motion; and we have reasons
for believing that the excitation of light will also give rise to
electrical circulation.

The question, whether plants possess sensation, whether they have
any disposition of parts at all analogous to the nervous system of
animals, has been often put forward, but as yet the answers have been
unsatisfactory. The point is one well worthy all the attention of
the vegetable physiologist; but regarding plants as the link between
the animal and the mineral kingdom,--looking upon phyto-chemistry,
as exhibited by them, as the means employed to produce those more
complex organizations which exist in animals,--we necessarily consider
plants as mere natural machines for effecting organic arrangements,
and, as such, that they cannot possess any nervous sensibility.
Muscular contraction may be represented in many of their marvellous
arrangements; and any disturbance produced by natural or artificial
means would consequently effect a change in the operations of those
forces which combine to produce vegetable life. Indeed, the experiments
of Carlo Matteucci, already referred to, prove that an incision across
a leaf, the fracture of a branch, or the mere bruising of any part of
the plant, interferes with the exercise of that power which, under the
operation of luminous agency, decomposes carbonic acid, and effects the
assimilation of the other elements.

To recapitulate. A plant is an organized creation; it is so in virtue
of certain strange phyto-chemical operations, which are rendered active
by the solar influences involved in the great phenomena of light, and
by the excitation of caloric force mid electrical circulation. It is
a striking exemplification of the united action of certain empyreal
powers, which give rise to the combination, of inorganic principles
under such forms that they become capable of obeying the mysterious
impulses of life.

The poet has imaged the agency of external powers in various shapes
of spiritualized beauty. From the goddess Flora, and her attendant
nymphs, to the romantic enchantress who called up flowers by the light
touch of her wand, we have, in all these creations, foreshadowings of
the discovery of those powers which science has shown are essential
to vegetable life. A power from without influences the plant; but the
animal is dependent upon a higher agency which is potent within him.

The poet’s dream pleases the imaginative mind; and, associating in our
ideas all that is graceful and loveable in the female form, with that
diviner feeling which impresses the soul with the sense of some unseen
spirituality, we perceive in the goddess, the enchantress, or the
sylph, pure idealizations of the physical powers. The spirit floating
over these forms of beauty, and adorning them with all the richness
of colour--painting the rose, and giving perfume to the violet--is,
in the poet’s mind, one which ascends to nearly the highest point of
etherealization, and which becomes, indeed, to him a spirit of light;
they ride upon the zephyrs, and they float, in all the luxury of an
empyreal enjoyment, down to the earth upon a sunbeam. Such is the
work of the imagination. What is the result of the search of plodding
science after truth? The sunbeam has been torn into rays, and every ray
tasked to tell of its ministry.

Nature has answered to some of the interrogations; and, passing over
all the earth, echoed from plant to plant, we have one universal cry
proclaiming that every function of vegetable life is due to the spirits
of the sun.

The mighty Adansonia of Senegal, hoary with the mosses of five
thousand years,--the Pohon upas in their deadly valleys,--the climbing
lianas of the Guiana forests,--the contorted serpent-cactus on the
burning hills,--the oaks, which spread their branches in our tempered
climes,--the glorious flowers of the inter-tropical regions, and
those which gem our virent plains,--the reindeer lichen of northern
lands, and the confervæ of the silent pool,--the greatest and humblest
creations of the vegetable world,--all proclaim their direct
dependence upon the mysterious forces which are bound together in the
silver thread of Light.

These undulations, pulsations too refined for mortal ears, which
quicken and guide these wonderful organisms, may be indeed regarded
as sphered music for ever repeating the Divine command, “_Let there
be Light_,” by the creation of which, a dark and dreary chaos was
moulded into a star of beauty, capable of radiating brightness to other
space-wandering worlds.


FOOTNOTES:

[248] Percy Bysshe Shelley.

[249] _Experiments on the production of dephlogisticated air from water
with various substances_: by Lieut.-General Sir Benjamin, Count of
Rumford; Phil. Trans., vol. lxxvii. p. 84.

[250] _Experiments upon Vegetables, discovering their great power of
purifying the common air in the Sunshine, and of injuring it in the
Shade and at Night; to which is joined, A new method of examining the
accurate degrees of Salubrity of the Atmosphere_, by John Ingenhousz,
Councillor of the Court, and Body Physician to their Imperial and Royal
Majesties, F.R.S., &c. London: printed for P. Elmsley, in the Strand,
and H. Payne, Pall Mall, 1779.

[251] _The Kingdoms of Nature, their life and affinity_: by Dr. C. G.
Carus; Scientific Memoirs, vol. i. p. 223.

[252] In _Biologie_, by G. R. Treviranus, vol. ii. p. 302, the
following passage occurs:--“If we expose spring water to the sun in
open or even closed transparent vessels, after a few days bubbles
rise from the bottom, or from the sides of the vessel, and a green
crust is formed at the same time. Upon observing this crust through
a microscope, we discover a mass of green particles, generally of a
round or oval form, very minute, and overlaid with a transparent mucous
covering, some of them moving freely, whilst others, perfectly similar
to these, remain motionless and attached to the sides of the vessel.
This motion is sometimes greater than at others. The animalcules
frequently lie as if torpid, but soon recover their former activity.”

[253] _On the Structure of the Vegetable Cell_: by Mohl.--Scientific
Memoirs, vol. iv. p. 113. _Outlines of Structural and Physical Botany_:
by Henfrey.

[254] Dr. Carus, in the memoir already quoted, says:--“But since, in
the organization of the earth, light and air, as constituting a second
integrant part, stand opposed to gravitation, and since the plant
bears a relation, not only to gravitation, but to light also, when its
formation is complete it will necessarily present a second anatomical
system, namely, that of the spiral vessels, which have been very justly
considered, of late, as the organs that perform in plants the functions
of nerves.”

[255] Mr. Crosse’s Experiments in the Journal of the London Electrical
Society, and Mr. Weekes in the Electrical Magazine, and a communication
appended to _Explanations: a Sequel to the Vestiges of the Natural
History of Creation_.

[256] _Die Metamorphose der Pflanzen_: Goethe, sect. 78.

[257] Lindley’s _Elements of Botany_.

[258] See the very curious experiments of C. Matteucci. Traduit et
extrait du “_Cimento_.”--Archives des Sciences Physiques et Naturelles;
_Quelques Expériences sur la Respiration des Plantes_. Nov. 1846.

[259] Consult _Rural Economy_, by J. B. Boussingault; _The Chemical and
Physiological Balance of Organic Nature_, by Dumas and Boussingault;
and _Agricultural Chemistry_, by Liebig.

[260] The practical value of the discovery now described, will be best
understood from the following letter from Mr. Lawson, of Edinburgh:--

Edinburgh, 1, George the Fourth’s Bridge, Sept. 8, 1853.

MY DEAR SIR,--I am favoured with yours of the 5th, relative to my
practical experience in the effect of the chemical agency of 
media on the germination of seeds and the growth of plants.

I must first explain that it is our practice to test the germinating
powers of all seeds which come into our warehouses before we send
them out for sale; and, of course, it is an object to discover, with
as little delay as possible, the extent that the vital principle is
active, as the value comes to be depreciated in the ratio it is found
to be dormant. For instance, if we sow 100 seeds of any sort, and the
whole germinate, the seed will be the highest current value; but if
only 90 germinate, its value is 10 per cent. less; if 80, then its
value falls 20 per cent.

I merely give this detail to show the practical value of this test, and
the influence it exerts on the fluctuation of prices.

Our usual plan formerly was to sow the seeds to be tested in a hot-bed
or frame, and then watch the progress and note the results. It was
usually from eight to fourteen days before we were in a condition to
decide on the commercial value of the seed under trial.

My attention was, however, directed to your excellent work, “On the
Physical Phenomena of Nature,” about five years ago, and I resolved to
put your theory to a practical test. I accordingly had a case made,
the sides of which were formed of glass  blue or indigo, which
case I attached to a small gas stove for engendering heat; in the case
shelves were fixed in the inside, on which were placed small pots
wherein the seeds to be tested were sown.

The results were all that could be looked for: the seeds freely
germinated in from two to five days only, instead of from eight to
fourteen days as before.

I have not carried our experiments beyond the germination of seeds, so
that I cannot afford practical information as to the effect of other
rays on the after culture of plants.

I have, however, made some trials with the yellow ray in preventing the
germination of seeds, which have been successful; and I have always
found the violet ray prejudicial to the growth of the plant after
germination.--I remain, my dear Sir,

Very faithfully yours, CHARLES LAWSON.




CHAPTER XV.

PHENOMENA OF ANIMAL LIFE.

  Distinction between the Kingdoms of Nature--Progress of Animal
    Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent
    Animals--Annelidans--Myriapoda--Animal
    Metamorphoses--Fishes--Birds--Mammalia--Nervous System--Animal
    Electricity--Chemical Influences--Influence of Light on Animal
    Life--Animal Heat--Mechanical Action--Nervous Excitement--Man and
    the Animal Races, &c.


“A stone grows; plants grow and live; animals grow, live, and feel.”
Such were the distinctions made by Linnæus, between the conditions
of the three kingdoms of nature. We cannot, however, but regard them
as in all respects illogical. The stone--a solid mass of unorganized
particles--enlarges, if placed in suitable conditions, by the accretion
of other similar particles around it; but it does not, according to any
meaning in which we use the word, _grow_. Plants and animals grow; and
they differ, probably, only in the phenomena of sensation. Yet, the
trembling mimosa, and several other plants, appear to possess as much
feeling as sponges and some of the lower classes of animals. By this
definition, however, of the celebrated Swedish naturalist, we have a
popular and simple expression of a great fact.

As we have only to examine the question of the agency of the physical
forces upon animal life, we must necessarily confine our attention to
the more striking phenomena with which science has made us acquainted;
and, having briefly traced the apparent order in which the advance of
organization proceeded, we must direct our few concluding remarks to
the physico-physiological influences, which we must confess to know but
too imperfectly.

We learn that, during the states of progress which geology, looking
into the arcana of time, has made us acquainted with, a great variety
of animal forms were brought into existence. They lived their periods.
The conditions of the surface of the earth, the sea, or the atmosphere,
were altered; and, no longer fitted for the enjoyments of the new life,
these races passed away, and others occupied their places, which, in
turn, went through all the stages of growth, maturity, and decay;
until at length, the earth being constituted for the abode of the
highest order of animals, they were called into existence; and man,
the intellectual monarch of the world, was placed supreme amongst them
all. Types of nearly all those forms of life which are found in the
fossil state are now in existence; and if we examine the geographical
distribution of animals--the zones of elevation over the surface of
the earth, and the zones of depth in the ocean,--we shall find, now
existing, animal creations strikingly analogous to the primitive forms
and conditions of the earth’s inhabitants. From the depths of the ocean
we may even now study--as that most indefatigable naturalist, Professor
Edward Forbes, has done--the varying states of organization under the
circumstances of imperfect light and varying temperature.[261]

The gradual advance of animal life in the ascending strata has led
to many speculations, ingenious and refined, on the progressive
development of animals. That the changes of the inorganic world have
impressed new conditions on the organic structures of animals, to meet
the necessities of their being, must be admitted. Comparative anatomy
has demonstrated that such supposed differences really existed between
the creatures of secondary formations--those of the tertiary and the
present periods. It has been imagined, but upon debatable foundations,
that the atmosphere, during the secondary periods, was highly charged
with carbonic acid; and, consequently, that though beneficial to the
growth of plants, and peculiarly fitted for the conditions required
by those which the fossil flora makes us acquainted with, it was not
adapted to support any animals above the slow-breathing, cold-blooded
fishes and reptiles. Under the action of the super-luxuriant vegetation
of these periods, this carbonic acid is supposed to have been removed,
an addition of oxygen furnished; and thus, consequently, the earth
gradually fitted for the abode of warm-blooded and quick-breathing
creatures. We do, indeed, find a very marked line between the fossil
remains of the lias formations which enclose the saurians, and the
wealden, in which birds make their appearance more numerously than in
any previous formation.

Founded upon these facts, speculations have been put forth on the
gradual development of animals from the lowest up to the highest
orders. Between the polype and man a continuous series has been
imagined, every link of the chain being traced into connection with
the one immediately succeeding it; and, through all the divisions,
zoophytes, fishes, amphibia, reptiles, birds, and mammalia are seen,
according to this hypothesis, to be derived by gradual advancement from
the preceding orders. The first having given rise to amphibia,--the
amphibion gives birth to the reptile,--the reptile advances to
the bird,--and from this class is developed the mammal. A slight
investigation will convince us that this view has no foundation.
Although a certain relationship may be found between some of the
members of one class, and those of the other immediately joining it,
yet this is equally discovered to exist towards classes more remote
from each other; and in no one instance can we detect anything like
the passage of an animal of one class into an animal of another. Until
this is done, we cannot but regard the forms of animal life as distinct
creations, each one fitted for its state of being, springing from the
command of the great First Cause.[262]

But it is time to quit these speculative questions, and proceed to the
examination of the general conditions of animal life at the present
time.

Lowest in the scale of animals, and scarcely distinguishable from a
vegetable, we find the sponge, attached to and passing its life upon
a rock, exhibiting, indeed, less signs of feeling than many of the
vegetable tribes. The chemical differences between vegetables and
sponges are, however, very decided; and we find in the tissues of the
sponge a large quantity of nitrogen, a true animal element, which
exists, but in smaller quantities, in vegetables.

These creations, standing between vegetable and animal life, possess
the singular power of decomposing carbonic acid, as plants do; and the
water in which they live always contains an excess of free oxygen.

The polypes are a remarkably curious class. “Fixed in large arborescent
masses to the rocks of tropical seas, or in our own climate attached
to shells or other submarine substances, they throw but their
ramifications in a thousand beautiful and plant-like forms; or,
incrusting the rocks at the bottom of the ocean with calcareous earth,
separated from the water which bathes them, they silently build up
reefs and shoals, justly dreaded by the navigator; and sometimes giving
origin, as they rise to the surface of the sea, to islands, which
the lapse of ages clothes with luxuriant verdure, and peoples with
appropriate inhabitants.”[263]

Most of the polypes are fixed and stationary; but the hydra and some
others have the power of changing their positions, which they do in
search of the light of the sun. They do not appear to have organs of
sight requiring light; but still they delight in the solar influences.
The most extraordinary fact connected with the hydra is its being
multiplied by division. If an incision be made in the side of a hydra,
a young polype soon developes itself; and if one of these creatures be
divided, it quickly restores the lost portion of its structure. The
varieties of the polypes are exceedingly numerous, and many of them are
in the highest degree curious, and often very beautiful. The actiniæ,
like flowers, appear to grow from the rocks, unfolding their tentacula
to the light; and, in the excitement due to their eagerness for prey,
they exhibit a beautiful play of colours and most interesting forms.
Microscopic zoophytes of the most curious shapes are found,--all of
which attest, under examination, the perfection of all created things.

Infusoria and animalcula,--animals, many of them, appearing under the
microscope as little more than a transparent jelly,--must be recognized
as the most simple of the forms of life. They exist in all waters in
uncountable myriads; and, minute creatures as they are, it has been
demonstrated that many of the great limestone hills are composed
entirely of their remains.

The acalephæ, or the phosphorescent animals of the ocean, are no less
curious. From creatures of the most minute size, they extend to a
considerable magnitude, yet they appear to be little more than animated
masses of sea-water. If any one of these sea-jellies, or jelly-fishes
as they are often called (even the largest varieties of them), is cast
upon the shore, it is soon, by the influence of the sun, converted into
a mere fibre no thicker than a cobweb: an animal weighing seven or
eight pounds is very soon reduced to as many grains. There are numerous
kinds of these singular creatures, most of which are remarkable for
the powerful phosphorescent light they emit. The _beroes_ and the
_pulmonigrade_ shine with an intense white light many feet below the
surface, whilst the _Cestum Veneris_, or girdle of Venus, gliding
rapidly along, presents, on the edge of the wave, an undulating riband
of flame of considerable length. There can be no doubt that this arises
from the emission of phosphorescent matter of an unknown kind from the
bodies of these animals.

The microscope has made us familiar with the mysteries of a minute
creation which we should not otherwise have comprehended. These
creatures are found inhabiting the waters and the land, and they exist
in the intestinal structure of plants and animals, preying upon the
nutritive juices which pass through their systems. Although these
beings are so exceedingly small that even the most practised observer
cannot detect them with the naked eye, they are proved, by careful
examination under the microscope, to be in many cases elaborately
organized. Ehrenberg has discovered in them filamentary nerves and
nervous masses, and even vessels appropriated to the circulation
of fluids, showing that they belong really to a high condition of
existence.

Passing over many links in that curious chain which appears to bind
the animal kingdom into a complete whole, we come to the articulata of
Cuvier--the homogangliata of Owen.

All those creatures which we have been hitherto considering are too
imperfect in the construction of their simple organizations to maintain
a terrestrial existence; they are, therefore, confined to a watery
medium. In the articulata, we have evidences of higher attributes,
and indications of instincts developed in proportion to the increased
perfection of organization. Commencing with the annelidans, all of
which, except the earthworms, are inhabitants of the waters, we
proceed to the myriapoda, presenting a system intermediate in every
respect between that of worms and insects; we then find embraced in
the same order, the class insecta, which includes flies and beetles
of all kinds; and, as the fourth division of articulated beings, the
arachnidans or spiders; and, lastly, the marine tribe of crustaceans.

The most remarkable phenomena connected with these animals are the
metamorphoses which they undergo. The female butterfly, for instance,
lays eggs, which, when hatched, produce caterpillars: these live in
this state for some time, feeding upon vegetables, and, after casting
their skins as they increase in size, at last assume an entirely
different state, and, dormant in their oblong case, they appear like
dead matter. This chrysalis, or pupa, is generally preserved from
injury by being embedded in the earth, from which, after a season, a
beautifully perfect insect escapes, and, floating on the breeze of
summer, enjoys its sunshine, and revels amidst its flowers.

No less remarkable is the metamorphosis of the caducibranchiate
amphibia, passing through the true fish condition of the tadpole to the
perfect air-breathing and four-footed animal, the frog.

A metamorphosis of the crustaceans, somewhat similar to that which
takes place in insects, has been of late years creating much discussion
amongst naturalists: but the question appears to be now settled by the
careful and long-continued observations of Mr. Thompson and Mr. R. C.
Couch.

A wide line of demarcation marks the separation of the invertebrata
from the four great classes of vertebrate animals--fishes, reptiles,
birds, and mammalia. Every part of the globe,--the ocean and the inland
lake,--the wide and far-winding river, and the babbling stream,--the
mountain and the valley,--the forest with its depth of shade, and
the desert with its intensity of light,--the cold regions of the
frost-chained north, and the fervid clime within the tropics--presents
for our study innumerable animals, each fitted for the conditions to
which it is destined; and through the whole we find a gradual elevation
in the scale of intelligence, until at last, separated from all by
peculiar powers, we arrive at man himself.

In each of these four classes the animals are furnished with a bony
skeleton, which is in the young animal little more than cartilage;
but, as growth increases, lime becomes deposited, and a sufficient
degree of hardness is thus produced to support the adult formation.
Some anatomists have endeavoured to show that even in the mechanical
structure of the bony fabrics of animals, we are enabled to trace a
gradual increase in the perfection of arrangement, from the fish until
the most perfect is found in man. Many of the mammalia, however, are
furnished with skeletons which really surpass that of man. These belong
to animals which depend for subsistence upon their muscular powers, and
with whom man is, in this particular, on no equality. What is the lord
of the creation, compared with the antelope for fleetness, or with the
elephant and many other animals for strength?

As we ascend the scale of animal life we find a more perfectly
developed nervous system; and the relative size of the brain, compared
with that of the brute, is found progressively to increase, until it
arrives at the utmost perfection in man. On the system of nerves
depends sensation, and there can be no doubt that the more exalted the
order of intelligence displayed, the more exquisitely delicate is the
nervous system. Thus, in this world, refined genius must necessarily be
attended with a condition of sensibility which, too frequently, to the
possessor is a state of real disease.

It must be evident to every reader that but very few of the striking
features of animal life have been mentioned in the rapid survey which
has been taken of the progress of animal organization. The subject
is so extensive that it would be quite impossible to embrace it
within any reasonable limits; and it furnishes matter so curious and
so instructive, that, having once entered on it, it would have been
difficult to have made any selection, and we must have devoted a volume
to the æsthetics of natural science. Passing it by, therefore, with the
mere outline which has been given, we must proceed to consider some of
the conditions of vitality.

Bell has proved that one set of nerves is employed in conveying
sensation to the brain, and another set in transferring the desires of
the will to the muscles. By the separation of a main branch of one of
the nerves of sensation, although all the operations of life will still
proceed, the organ to which that nerve goes is dead to its particular
sense. In like manner, if one of the nerves of volition is divided,
the member will not obey the inclination of the brain. It is evident,
therefore, although many of the great phenomena of vital force are
dependent on the nervous system, and the paralysis of a member ensues
upon the separation or the disease of a nerve, that the nerves are but
the channels through which certain influences are carried. The _vis
vitæ_ or vital principle--for we are compelled by the imperfection of
our knowledge to associate under this one term the ultimate causes of
many of the phenomena of life--is a power which, although constantly
employed, has the capability of continually renewing itself by
some inexplicable connection existing between it and many external
influences. We know that certain conditions are necessary to the health
of animals. Diseased digestion, or any interruption in the circulation
of the blood, destroys the vital force, and death ensues. The processes
of digestion and of the circulation are perfectly understood, yet we
are no nearer the great secret of the living principle.

Animals are dependent on several external agents for the support of
existence. The oxygen of the air is necessary for respiration. Animal
heat, as will be shown presently, is in a great measure dependent
upon it. The external heat is so regulated that animal existence is
comfortably supported. Electricity is without doubt an essential
element in the living processes; and, indeed, many physiologists have
been inclined to refer vital force to the development of electricity
by chemical action in the brain. This view has, however, no foundation
in experiment beyond that afforded by the appearance of electric
currents, when the brain is excited. This proves no more than that the
operations of mind develope physical power in the matter with which it
is mysteriously connected.

The phenomena of the Torpedo and Gymnotus we have already noticed,[264]
and there are other creatures which certainly possess the power of
secreting and discharging electricity. Galvani’s experiments, and
those of Aldini, appear to show--and the more delicate researches of
Matteucci have satisfactorily determined--that currents of electricity
are always circulating in the animal frame;--that positive electricity
is constantly passing from the interior to the exterior of a muscle.
Matteucci, by arranging a series of muscles, has formed an electric
pile of some energy.[265] These currents have been detected in man, in
pigeons, fowls, eels, and frogs.

In the human body it is evident a large quantity of electricity
exists in a state of equilibrium. Du Bois Raymond has shown that we
may by mere muscular motion give rise to electric currents which can
be measured by the galvanometer. This, however, may be said of every
substance. It is perhaps more easily disturbed in the human system;
indeed, the manifestation of sparks from the hair and other parts of
the body by friction is not uncommon. Every chemical action, it has
been already shown, gives rise to electrical manifestations; and the
animal body is a laboratory, beautifully fitted with apparatus, in
which nearly every chemical process is going on. It has been proved
that acid and alkaline principles are constantly acting upon each
other through the tissues of the animal frame; and we have the curious
phenomena of endosmose and exosmose in constant effort, and catalysis
or _surface force_, operating in a mysterious manner.[266]

With the refined physiological questions connected with the phenomena
of sensation we cannot deal, nor will any argument be adduced for or
against the hypothesis which would refer these phenomena to some
extraordinary development of electric force in the brain. The entire
subject appears to stand beyond the true limits of science, and every
attempt to pass it is invariably found to lead to a confused mysticism,
in which the real and the ideal are strangely confounded. Science stops
short of the phenomena of vital action.

We cannot, however, but refer to the idea entertained by many that the
brain is an electric battery, and the nerves a system of conductors.
On this view Sir John Herschel remarks:--“If the brain be an electric
pile constantly in action, it may be conceived to discharge itself
at regular intervals, when the tension of the electricity reaches a
certain point, along the nerves which communicate with the heart, and
thus excite the pulsation of that organ.” Priestley, however, appears
to have been the first to promulgate this idea.

Light is an essential element in producing the grand phenomenon of
life, though its action is ill understood. Where there is light,
there is life, and any deprivation of this principle is rapidly
followed by disease of the animal frame, and the destruction of the
mental faculties. We have proof of this in the squalor of those whose
necessities compel them to labour in places to which the blessings
of sunshine never penetrate, as in our coal-mines, where men having
everything necessary for health, except light, exhibit a singularly
unhealthy appearance. The state of fatuity and wretchedness to which
those individuals have been reduced who have been subjected for
years to incarceration in dark dungeons, may be referred to the same
deprivation. Again, in the peculiar aspect of those people who inhabit
different regions of the earth under varying influences of light, we
see evidence of the powerful effects of solar action. Other forces, as
yet undiscovered, may, in all probability do, exert decided influences
on the animal economy; but, although we recognize many effects which we
cannot refer to any known causes, we are perfectly unable to imagine
the sources from which they spring.

It will be interesting now to examine the phenomena of animal heat, the
consideration of which naturally leads us to consider the digestive
system, the circulatory processes, and the effects of nervous
excitation.

The theory, which attributes animal heat to the combination of the
carbon of the food taken into the stomach with the oxygen of the air
inspired through the lungs, has become a very favourite one. It must,
however, be remembered that it is by no means new. The doctrines of
Brown, known as the Brunonian system, and set forth in his _Elementa
Medicinæ_, are founded upon similar hasty generalizations. Although,
without doubt, true in a certain degree, it is not so to the extent
to which its advocates would have us believe. That the carbonaceous
matter received into the stomach, after having undergone the process
of digestion, enters into combination with the oxygen breathed through
the lungs or absorbed by the skin, and is given off from the body in
the form of carbonic acid, and that, during the combination, heat is
produced, by a process similar to that of ordinary combustion, is an
established fact; but the idea of referring animal heat entirely to
this chemical source, when there are other well-known causes producing
calorific effects, is an example of the errors into which an ingenious
mind may be led, when eagerly seeking to establish a favourite
hypothesis.

Animal and vegetable diet, which is composed largely of carbon and
hydrogen, passes into the digestive system, and becomes converted into
the various matters required for the support of the animal structure.
The blood is the principal fluid employed in distributing over the
system the necessary elements of health and vigour, and for restoring
the waste of the body. This fluid, in passing through the lungs,
undergoes a very remarkable change, and not merely assumes a different
colour, but really acquires new properties, from its exposure to the
air with which the cells of these organs are filled. By a true chemical
process, the oxygen is separated from the air, that oxygen is made to
combine with the carbon and hydrogen, and carbonic acid and water are
formed. These are liberated and thrown off from the body either through
the lungs or by the skin. In the processes of life, as far as we are
enabled to trace them, we see actions going on which are referred to
certain causes which we _appear_ to explain. Thus, the combination of
the oxygen of the air with the carbon of the blood is truly designated
a case of chemical affinity; and we find that in endeavouring to
imitate the processes of nature in the laboratory, we are, to a certain
extent, successful. We can combine carbon and oxygen to produce
carbonic acid; and we know that the result of that combination is the
development of certain definite quantities of heat. Let us examine the
conditions of this chemical phenomenon, and we shall find that in the
natural and artificial processes,--for we must be allowed to make that
distinction,--there are analogous circumstances. If we place a piece of
pure carbon, a lump of charcoal or a diamond, in a vessel of air, or
even of pure oxygen gas, no change will take place in either of these
elements, and, however long they may be kept together, they will still
be found as carbon or diamond, and oxygen gas. If we apply heat to the
carbon until it becomes incandescent, it immediately begins to combine
with the oxygen gas,--it burns;--after a little time all the carbon has
disappeared, and we shall find, if the experiment has been properly
made, that a gas is left behind which is distinguished by properties
in every respect the reverse of those of oxygen, supporting neither
life nor combustion, whereas oxygen gives increased vigour to both.
We have now, indeed, carbonic acid gas formed by the union of the two
principles.

A dead mass of animal matter may be placed in oxygen gas, and, unless
some peculiar conditions are in some way brought about, no change will
take place; but, if it were possible to apply the _spark of life_ to
it, as we light up the spark in the other case, or if, as that is
beyond the power of man, we substitute a living creature, a combination
between the carbon of the animal and the gas will immediately begin,
and carbonic acid will be formed by the waste of animal matter, as in
the other case it is by the destruction of the carbon; and, if there is
not a fresh supply given, the animal must die, from the exhaustion of
its fabric. Now, in both these cases, it is clear that, although this
chemical union is a proximate cause of heat, there must be existing
some power superior to it, as the ultimate cause thereof.

The slow combustion (_eremacausis_) of vegetable matter, decomposing
under the influence of moisture and the air, does not present similar
conditions to those of the human body, although it has been insisted
upon to be in every respect analogous. That the results resemble each
other is true, but we must carefully distinguish between effects and
causes; and the results of chemical decomposition in inert matter
differ from those in the living organism. The vegetable matter has lost
the principle of organic life, and, that gone, the tendency of all
things being to be resolved into their most simple forms, a disunion of
the elements commences: oxygen, hydrogen, and carbon pass off either
in the gaseous state or as water, whilst some carbon is liberated in
a very finely-divided condition, and enters slowly into combination
with oxygen supplied by the water or the air. Hydrogenous compounds
are at the same time formed, and, under all these circumstances, as in
all other chemical phenomena, an alteration of temperature results.
Heat results from the chemical changes, and eventually true combustion
begins.

The animal tissue may act in the same way as platina has already
been shown to act in producing combination between gases; but of this
we have no proof. We know that electricity is capable of producing
the required conditions, and we also learn, from the beautiful
researches of Faraday, that the quantity of electricity developed
during decomposition is exactly equal to that required to effect the
combination of the same elements. Thus it is quite clear that, during
the combination of the carbon of the blood with the oxygen of the air,
a large amount of electricity must become latent in the compound. The
source of this we know not: it may be derived from some secret spring
within the living structure, or it may be gathered from the matter
surrounding it. There is much in nervous excitation which appears like
electrical phenomena, and attempts have been frequently made to refer
sensation to the agency of electricity. But these are the dreams of the
ingenious, for which there is but little waking reality.

Every mechanical movement of the body occasions the development of
heat; every exertion of the muscles produces sensible warmth; and,
indeed, it can be shown by experiment that every expansion of muscular
fibre is attended with the escape of caloric, and its contraction
with the absorption of it. There are few operations of the mind which
do not excite the latent caloric of the body, and frequently we find
it manifested in a very remarkable manner by a suddenly-awakened
feeling. The poet, in the pleasure of creation, glows with the ardour
of his mind, and the blush of the innocent is but the exhibition
of the phenomenon under some nervous excitation, produced by a
spirit-disturbing thought. Thus we see that the processes of digestion
and respiration are not the only sources of animal heat, but that many
others exist to which much of the natural temperature of the body must
be referred.

So much that is mysterious belongs to the phenomena of life, that
superstition has had a wide scope for the exercise of its influence;
and through all ages a powerful party of mankind have imagined that
the spirit of human curiosity must be checked before it advances to
remove the veil from any physiological causes. Hence it is that even at
the present day so much that stands between what, in our ignorance, we
call the real and the supernatural, remains uninvestigated. Even those
men whose minds are sceptical upon any development of the truths of
great natural phenomena,--who, at all events, will have proof before
they admit the evidence, are ready to give credit to the grossest
absurdities which may be palmed upon them by ingenious charlatans,
where the subject is man and his relations to the spiritual world.

Man, and the races of animals by which he is surrounded, present a
very striking group, consider them in whatever light we please. The
gradual improvement of organic form, and the consequent increase of
sensibility, and eventually the development of reason, are the grandest
feature of animated creation.

The conditions as to number even of the various classes are not the
least remarkable phenomena of life. In the lowest orders of animals,
creatures of imperfect organization,--consequently those to whom the
conditions of pain must be nearly unknown,--increase by countless
myriads. Of the infusoria and other beings, entire mountains have
been formed, although microscopes of the highest powers are required
to detect an individual. Higher in the scale, even among insects, the
same remarkable conditions of increase are observed. Some silkworms lay
from 1,000 to 2,000 eggs; the wasp deposits 3,000; the ant from 4,000
to 5,000. The queen bee lays between 5,000 and 6,000 eggs according to
Burmeister; but Kirby and Spence state that in one season the number
may amount to 40,000 or 50,000. But, above all, the white ant (_Termes
fatalis_) produces 86,400 eggs each day, which, continuing for a
lunar month, gives the astonishing number of 2,419,200, a number far
exceeding that produced by any known animal.

These may appear like the statements in which a fictionist might
indulge, but they are the sober truths discovered by the most
pains-taking and cautious observers. And it is necessary that such
conditions should prevail. These insects, and all the lower tribes of
the animal kingdom, furnish food for the more elevated races. Thousands
are born in an hour, and millions upon millions perish in a day. For
the support of organic life, like matter is required; and we find that
the creatures who are destined to become the prey of others are so
constituted that they pass from life with a perfect unconsciousness of
suffering. As the animal creation advances in size and strength, their
increase becomes limited; and thus they are prevented from maintaining
by numbers that dominion over the world which they would be enabled
from their powers to do, were their bands more numerous than we now
find them.

The comparative strength, too, of the insect tribes has ever been a
subject of wonder and of admiration to the naturalist. The strength of
these minute creatures is enormous; their muscular power, in relation
to their size, far exceeds that of any other animal. The grasshopper
will spring two hundred times the length of its own body. The
dragonfly, by its strength of wing, will sustain itself in the air for
a long summer day with unabated speed. The house-fly makes six hundred
strokes with its wings, which will carry it five feet, every second.
The stag-beetle, were it the size of the elephant, would be able to
tear up the largest mountains.

Such are the wonders of the natural world; from the zoophyte, growing
like a flowering plant[267] upon an axis filled with living pith--a
small remove from the conditions of vegetable life, upwards through the
myriads of breathing things--to man, we see the dependence of all upon
these physical powers which we have been considering.

To trace the effects of those great causes through all their mysterious
phases is the work of inductive science; and the truths discovered tend
to fit us for the enjoyment of the eternal state of high intelligence
to which every human soul aspires.

That which the ignorant man calls the supernatural, the philosopher
classes amongst natural phenomena. The ideal of the credulous man
becomes the real to him who will bend his mind to the task of inquiry.
Therefore to attempt to advance our knowledge of the unknown, to add
to the stores of truth, is an employment worthy the high destiny of
the human race. Remembering that the revelations of natural science
cannot in any way injure the revelation of eternal truth, but, on
the contrary, aid to establish in the minds of the doubting a firm
conviction of its Divine origin and of man’s high position, we need
never fear that we are proceeding too far with any inquiry, so long as
we are cautious to examine the conditions of our own minds, that they
be not made the dupe of the senses.

In the fairies of the hills and valleys, in the gnomes of the caverns,
in the spirits of the elements, we have the attempts of the mind, when
the world was young, to give form to the dim outshadowings of something
which was then felt to be hidden behind external nature.

In the Oread, the Dryad, and the Nereid, we have, in like manner, an
embodiment of powers which the poet-philosopher saw in his visions
presiding over the mountain, the forest, and the ocean. Content with
these, invested as they were with poetic beauty, man for ages held
them most religiously sacred; but the progress of natural science
has destroyed this class of creations. “Great Pan is dead,” but the
mountains are not voiceless; they speak in a more convincing tone; and,
instead of the ear catching the dying echo of an obscure truth, it is
gladdened with the full, clear note of nature in the sweetest voice
proclaiming secrets which were unknown to the dreams of superstition.


FOOTNOTES:

[261] _Reports of the Fauna of the Ægean_: by Professor
Forbes.--Reports of the British Association. _On the Physical
Conditions affecting the Distribution of Life in the Sea and the
Atmosphere, &c._: by Dr. Williams. Swansea.

[262] _The Vestiges of the Natural History of Creation._

[263] _General Outline of the Animal Kingdom_: by Professor Thomas
Rymer Jones, F.Z.S.

[264] In addition to the memoirs already referred to, Note p. 211,
see Carlisle, _On the battery of the Torpedo, governed by a voluntary
muscle_.--Phil. Trans., vol. xcv. p. 11. Todd, _Experiments on the
Torpedo of the Cape of Good Hope_.--Ibid., vol. cvi. p. 120. Todd,
_Experiments on the Torpedo Electricus at La Rochelle_.--Ibid., vol.
cvii. p. 32.

[265] For a concise account of these experiments see _Elements of
Natural Philosophy_: by Golding Bird, A.M., M.D., &c. 3rd Edition,
chap, xx p. 336. In this work all the most recent researches are given,
and the authorities referred to; see also Matteucci’s interesting
papers already quoted.

[266] _On the laws according to which the mixing of fluids, and their
penetration into permeable substances, occurs, with special reference
to the processes in the Human and Animal Organism_, by Julius Vogel, of
Giessen: translated for the Cavendish Society. Liebig, _On the Motion
of the Juices in the Animal Body_.

[267] _A General Outline of the Animal Kingdom_: by Thomas Rymer Jones,
p. 54, et seq.




CHAPTER XVI.

GENERAL CONCLUSIONS.

  The Changes produced on Physical Phenomena by the Movement of
    the Solar System considered--Exertion of the Physical Forces
    through the Celestial Spaces--The Balance of Powers--Varieties
    of Matter--Extension of Matter--Theory of Nonentity--A Material
    Creation an indisputable fact--Advantages of the Study of
    Science--Conclusion.


We have examined terrestrial phenomena under many of the harmonious
conditions which, with our limited intelligence, we can reach by the
aid of science. From the first exhibition of force, in the cohesion
of two atoms, onward to the full development of organic form in the
highest order of animals, we have observed strange influences. We
have seen the solitary molecule invested with peculiar properties,
and regulated by mighty forces; we have learned that the modes of
motion given to this beautiful sphere produce curious changes in the
operation of these powers; and we may with safety infer that every atom
constituting this globe is held in wonderful suspension against every
atom of every star, in the celestial spaces, even to that bright orb in
the centre of the Pleiades, around which the entire system of created
worlds is supposed to roll.

As we move around our own sun--in the limited period of 365 days, and
round our own axis in 24 hours--we experience transitions from heat to
cold, dependent upon our position in regard to that luminary and the
laws which regulate the reception and retention of certain physical
forces. May we not therefore conclude, without being charged with
making any violent deduction, that in the great revolution of our
system around the centre of space, we are undergoing gradual changes
which are essential to the great scheme of creation, though at present
incomprehensible to us?

In our consideration of the influence of time on the structure of
the earth as we find it, we discovered that, in ages long past, the
vegetation of the tropics existed upon these northern parts of the
globe; and geological research has also proved that over the same lands
the cold of an arctic winter must have long prevailed--the immense
glaciers of that period having left the marks of their movements upon
the face of the existing rocks.[268] We know that during 3,000 years
no change of temperature has taken place in the European climate.
The children of Israel found the date and the vine flourishing in
Canaan; and they exist there still. Arago has shown that a trifling
alteration of temperature would have destroyed one or the other of
these fruit-bearing trees, since the vine will not ripen where the mean
temperature of the year is higher than 84°, or the date flourish where
it sinks below that degree.

How immense, then, the duration of time since these changes must have
taken place! The 432,000 years of Oriental mythology is a period
scarcely commensurable with these effects; yet, to the creature of
three-score years, that period appears an eternity. The thirty-three
millions of geographical miles which our solar system traverses
annually, if multiplied by three thousand years, during which we know
no change has taken place, give us 99,000,000,000 as the distance
passed over in that period. How wide, then, must have been the journey
of the system in space to produce the alteration in the physical
powers, by which these changes have been effected!

We have an example, and a striking one, of the variations which may
be produced in all the physical conditions of a world, in those
disturbances of Uranus which led to the discovery of Neptune. For
thirty years or more certain perturbations were observed in this
distant planet, the discovery of Sir William Herschel, and calculation
pointed to some still more remote mass of matter as the cause, which
has been verified by its actual discovery. But now Uranus is at
rest;--quietly that star progresses in its appointed orbit,--Neptune
can no longer, for the present, cause it to move with greater or less
rapidity--they are too remote to produce any sensible influence upon
each other. Consequently, for thirty years, it is evident, phenomena
must have occurred on the surface of Uranus, which can be no longer
repeated until these two planets again arrive at the same positions
in their respective paths which they have occupied since 1812. These
considerations assist us in our attempts to comprehend infinite time
and space; but the human mind fails to advance far in the great
sublimity.

Through every inch of space we have evidence of the exercise of such
forces as we have been considering. Gravitation chains world to world,
and holds them all suspended from the mystic centre. Cohesion binds
every mass of matter into a sphere, while motion exerts a constant
power, which tends to alter the form of the mass. The earth’s form--a
flattened spheroid--the rings of Saturn and of Neptune are the
consequences of motion in antagonism to cohesion. Heat, radiating
from one planet to another, does its work in all, giving variety to
matter. Light seeks out every world--each trembling star tells of the
mystery of its presence. Where light and heat are, chemical action,
as an associated power, must be present; and electricity must do its
wondrous duties amongst them all. Modified by peculiar properties of
matter, they may not manifest themselves in phenomena like those of our
terrestrial nature; but the evidence of light is a sufficient proof of
the presence of its kindred elements; and it is difficult to imagine
all these powers in action without producing some form of organization.
In the rounded pebble which we gather from the sea-shore, in the medusa
floating bright with all the beauty of prismatic colour in the sun-lit
sea,--in the animal, mighty in his strength, roaming the labyrinthine
forests, or, great in intelligence, looking from this to the mysteries
of other worlds,--in all created things around us, we see direct
evidence of a beautiful adjustment of the balance of forces, and the
harmonious arrangement of properties.

One atom is removed from a mass and its character is changed; one
force being rendered more active than another, and the body, under its
influence, ceases to be the same in condition. The regulation which
disposes the arrangements of matter on this earth, must exist through
the celestial spaces, and every planet bears the same relation to every
other glittering mass in heaven’s o’erarching canopy, as one atom
bears to another in the pebble, the medusa, the lion, or the man. An
indissoluble bond unites them all, and the grain of sand which lies
buried in the depth of one of our primary formations, holds, chained
to it by these all-pervading forces, the uncounted worlds which, like
luminous sand, are sprinkled by the hand of the Creator through the
universe. Thus we advance to a conception of the oneness of creation.

The vigorous mind of that immortal bard who sang “of man’s first
disobedience,” never, in the highest rapture, the holiest trance of
poetic conception, dreamed of any natural truths so sublime as those
which science has revealed to us.

The dependence of all the systems of worlds upon each other, every
dust composing each individual globe being “weighed in a balance,” the
adjustment of the powers by which every physical condition is ordered,
the disposition of matter in the mass of the earth, and the close
relation of the kingdoms of nature,--are all revelations of natural
truths, exalting the mind to the divine conception of the universe.

There is a remarkable antagonism displayed in the operation of many
of these forces. Gravitation and cohesion act in opposition to the
repellent influences of caloric. Light and heat are often associated
in a very remarkable manner; but they are certainly in their radiant
states in antagonism to chemical action, whether produced by the direct
agency of actinic force, or through the intermediate excitement of
the electrical current.[269] And in relation to chemical force, as
manifested in organic combinations, we have the all-powerful operation
of LIFE preventing any exercise of its decomposing power.[270] As world
is balanced against world in the universe, so in the human fabric, in
the vegetable structure, in the crystallized gem, or in the rude rock,
force is weighed against force, and the balance hangs in tranquillity.
Let but a slight disturbance occasion a vibration of the beam, and
electricity shakes the stoutest heart with terror, at the might of its
devastating power.[271] Heat melts the hardest rocks, and the earth
trembles with volcanic strugglings; and actinic agency, being freed
from its chains, speedily spreads decay over the beautiful, and renders
the lovely repulsive.

We know matter in an infinite variety of forms, from the most ponderous
metal to the lightest gas; and we have it within our power to render
the most solid bodies invisible in the condition of vapour. Is it not
easy, then, to understand that matter may exist equally attenuated
in relation to hydrogen, as that gas itself is, when compared with
the metal platinum? A doubt has been raised against this view, from
the difficulty of accounting for the passage of the physical elements
through solid masses of matter. If we, however, remember that the known
gases have the power of transpiration through matter in a remarkable
degree,[272] and that the passage of water through a sieve may be
prevented by heat, it will be at once apparent that the permeation of
any radiant body through fixed solid matter is entirely a question of
conditions.

We can form no idea of the size of the ultimate atom; we cannot
comprehend the degree of etherealization to which matter may be
extended. Our atmosphere, we have seen, is only another condition of
the same elements which compose all the organized forms of matter
upon the earth, and, at the height reached by man, it is in a state
of extreme attenuation. What must be its condition at the distance
of forty miles from the earth? According to known laws, certain
phenomena of refraction have led us to set these bounds to the matter
constituting our globe: but it may exist in such a state of tenuity,
that no philosophical instrument constructed by human hands could
measure its refracting power; and who shall declare with certainty that
matter itself may not be as far extended as we suppose its influences
to be?

“Hast thou perceived the breadth of the earth? declare if thou knowest
it all.

“Knowest thou the ordinances of heaven? Canst thou set the dominion
thereof in the earth?”

A cheerless philosophy, derived from the transcendentalism of the
German schools, by an unhappy metaphysical subtlety, and grafted
upon what professes to be a positive philosophy, but which is not
so, is spreading amongst us, and would teach us to regard all things
as the mere exhibition of properties, a manifestation of powers; it
believes not in a material creation. The grandeur of the earth, and
the beautiful forms adorning it, are not entities. Yonder exquisite
specimen of the skill of man, in which mind appears to shine through
the marble,--that distant mountain which divides the clouds as they are
driven by the winds across it,--those trees, amid whose branches the
birds make most melodious music,--this flower, so redolent of perfume,
so bright in colour, and so symmetric in form,--and that lovely being
who, a model of beauty and grace, walks the earth an impersonation
of love and charity blended, making, indeed, “a sunshine in a shady
place,” are not realities. Certain forces combine to produce effects,
all of which unite to deceive poor man into the belief that he is a
material being, and the inhabitant of a material world. There may be
ingenuity in the philosophy of this school; its metaphysics may be of
a high order; but it evidently advances from the real to the ideal
with such rapidity, that every argument is based on an assumption
without a proof; every assumption being merely a type of the philosophy
itself,--a baseless fabric, a transcendental vision.

A material creation surrounds us. This earth, all that it contains, and
the immense hosts of stellar worlds, are absolute entities, surrounded
with, and interpenetrated by, certain exhibitions of creative
intelligence, which perform, according to fixed laws, the mighty
labours upon which depend the infinite and eternal mutations of matter.
The origin of a grain of dust is hidden from our finite comprehensions;
but its existence should be a source of hope, that those minds which
are allowed the privilege of tracing out its marvellous properties,--of
examining the empyreal principles upon which its condition, as a grain
of dust, depends,--and even of reducing these giant elements to do our
human bidding,--may, after a period of probation, be admitted to the
enjoyment of that infinite power to which the great secrets of creation
will be unveiled.

Every motion which the accurate search of the experimentalist has
traced, every principle or power which the physicist has discovered,
every combination which the chemist has detected, every form which the
naturalist has recorded, involves reflections of an exalting character,
which constitute the elements of the highest poetry. The philosophy of
physical science is a grand epic, the record of natural science a great
didactic poem.

To study science for its useful applications merely, is to limit its
advantages to purely sensual ends. To pursue science for the sake of
the truths it may reveal, is an endeavour to advance the elements
of human happiness through the intelligence of the race. To avail
ourselves of facts for the improvement of art and manufactures, is
the duty of every nation moving in the advance of civilization. But
to draw from the great truths of science intelligible inferences and
masterly deductions, and from these to advance to new and beautiful
abstractions, is a mental exercise which tends to the refinement and
elevation of every human feeling.

The mind thus exercised during the mid-day of life, will find in the
twilight of age a divine serenity; and, charmed by the music of nature,
which, like a vesper hymn poured forth from pious souls, proclaims
in devotion’s purest strain the departure of day, he will sink into
the repose of that mysterious night which awaits us all, tranquil in
the happy consciousness that the sun of truth will rise in unclouded
brilliancy, and place him in the enjoyment of that intellectual light,
which has ever been among the holiest aspirations of the human race.

The task of wielding the wand of science,--of standing a scientific
evocator within the charmed circle of its powers, is one which leads
the mind through nature up to nature’s God.

Experiment and observation instruct us in the discovery of a
fact;--that fact connects itself with natural phenomena,--the ultimate
cause of which we learn from Divine revelation, and receive in full
belief,--but the proximate causes are reserved as trials of man’s
intelligence; and every natural truth, discovered by induction,
enables the contemplative mind to deduce those perfect laws which are
exemplifications of the fresh-springing and all enduring POETRY OF
SCIENCE.


FOOTNOTES:

[268] “As to the polishing and grooving of hard rocks, it has lately
been ascertained that glaciers give rise to these effects when pushing
forward sand, pebbles, and rocky fragments, and causing them to grate
along the bottom. Nor can there be any doubt that icebergs, when they
run aground on the floor of the ocean, imprint similar marks upon
it.”--_Principles of Geology, or the modern changes of the Earth and
its Inhabitants considered as illustrative of Geology_: by Charles
Lyell, M.A., F.R.S. _Travels through the Alps of Savoy, and other parts
of the Pennine Chain, with Observations on the Phenomena of Glaciers_:
by James D. Forbes, F.R.S.

[269] This may be readily proved by the following simple but
instructive experiment:--Take two pairs of watch-glasses; into one pair
put a solution of nitrate of silver, into the other a weak solution
of iodide of potassium; connect the silver solution of each pair with
the potash one by a film of cotton, and carry a platina wire from one
glass into the other. Place one series in sunshine, and the other
in a dark place. After a few hours it will be found that the little
galvanic arrangement in the dark will exhibit, around the platina
wire, a very pretty crystallization of metallic silver, but no such
change is observable in the other exposed to light. If a yellow glass
is interposed between the glass and the sunshine, the action proceeds
as when in the dark. This experiment is naturally suggestive of many
others, and it involves some most important considerations.

[270] In cases of violent death it is often found the gastric juice
has, in a few hours, dissolved portions of the stomach.--Dr. Budd’s
Lecture before the College of Physicians.

[271] Faraday’s _Experimental Researches_, vol. i.; from which a
quotation has already been made, showing the enormous quantity of
electricity which is latent in matter.

[272] _On the Motion of Gases_: by Professor Graham, F.R.S.--Phil.
Trans., vol. cxxxvi. p. 573.




INDEX.


  Absorption of heat by air, water, and earth, 74.

  ---- of light, 125.

  Acalephæ, or phosphorescent animals, 387.

  Actinism, 166.

  ---- producing chemical change, 174.

  ---- and light antagonistic, 177.

  ----, influence of, on plants, 372.

  Action of presence--_Catalysis_, 280.

  “Active principles” of Newton, 11.

  Adams on planet Neptune, 32.

  Adiathermic bodies, 95.

  Aërial currents dependent on heat, 80.

  ---- chemical, 274.

  Affinity, 292.

  Age of the world, 404.

  Aggregation, attraction of, 48.

  ----, crystalline, 58.

  Agonic lines, 244.

  Air, absorption of heat by, 74.

  ---- density of the, 319.

  Alchemy, Nature’s, 293.

  Aldini on animal electricity, 393.

  Allotropic conditions of atoms, 43.

  Allotropism, 330.

  Allotropy, 291.

  Alum, opacity to heat rays, 65.

  Alpinus’ theory of matter, 47.

  Ammonites of the lias, 341.

  Ammoniacal amalgam, 325.

  Ampère’s theory of magnetism, 239.

  Analogy, dangers of reasoning by, 152.

  Ancients’ knowledge of magnetism, 235.

  Animals, phosphorescence of, 154.

  ---- respiration of, 310.

  ---- articulated, 388.

  Animal magnetism, 267.

  ---- electricity, 211, 392.

  ---- life, progress of, 338.

  ----, phenomena of, 383.

  Arago on the surface of the sun, 123.

  ---- on copying the Egyptian temples, 177.

  ---- on magnetic variation, 246.

  _Arbor Dianæ_--silver tree, 261.

  Aristotle on motion, 10.

  Atmosphere, uses of the, 319.

  Atmospheric refraction, 322.

  Atomic theory, 278.

  ---- volumes, 287.

  Atoms, allotropic state of, 43.

  Atom, the organic, 360.

  ----, ultimate size of, 408.

  ----, the, and its powers, 3.

  Attraction, chemical, 275.

  Aurora of the sun, 186.


  Back’s account of Aurora, 249.

  Balance of forces, 14.

  Bartholin on Iceland spar, 140.

  Beccaria, Father, on phosphorescence, 160.

  Becquerel’s experiments on electricity, 227.

  ---- on ozone, 300.

  Bell on the nerves, 391.

  Belemnites, 341.

  Berkeley, Bishop, on motion, 10.

  Berzelius on allotropy, 44.

  ---- on catalysis, 281.

  Biela’s comet, 26.

  Biot on polarization, 145.

  Bolognian stone, 161.

  Bouguer on the absorption of light by the atmosphere, 126.

  Boutigny on heat, 107.

  _Boletus igniarius_, 102.

  Boyle on motion, 9.

  Brain and nerves, 391.

  Brahminical philosophy, 245.

  Brewster, Sir D., refers magnetism to the sun, 263.

  ---- on magnetism, 247.

  Brown’s doctrines of life, 395.

  Butterfly, metamorphosis of, 389.


  Cagniard de la Tour state, 106.

  Calorific transparency, 65.

  ---- influence on plants, 376.

  Calotype, the, 174.

  Canton’s phosphorus, 161.

  Carbon, allotropic state of, 43.

  Carboniferous plants, fossil, 339.

  Carbonic acid, solid, 111.

  ---- quantity in atmosphere, 311.

  Cassini on magnetic variation, 246.

  Catalysis, 280.

  Cell, organic, 361.

  Cellini, Benvenuto, on the carbuncle, 159.

  Central sun, doctrine of a, 27.

  Changes, physical, 290.

  Chemical phenomena developing heat, 42.

  ---- decomposition producing heat, 97.

  ---- combination by heat, 98.

  ---- affinity suspended by heat, 109.

  ---- radiations, 166.

  ---- power of solar rays in the Tropics, 177.

  ---- agency of luminous rays, 178.

  ---- action influenced by magnetism, 252.

  ---- forces, 270.

  ---- elements, 272.

  ---- proportions, 285.

  ---- metamorphoses, 289.

  ---- phenomena, 295.

  ---- composition of atmosphere, 322.

  ---- rays, action of, on germination, 375.

  Chemistry, Electro, 206.

  ---- of Nature, 270.

  ---- Animal, 396.

  Chinese knowledge of magnet, 236.

  Chlorophylle, formation of, 373.

  Chloride of sulphur, transparency of, to heat, 65.

  Chlorine and hydrogen combine by light, 171.

  Chlorine in the ocean, 303.

  Cholera and electricity, 215.

  Choroid coat, the, 149.

  Chromatic lines on the earth, 133.

  Clay converted into slate by electricity, 227.

  Climate of the earth, 350.

  Clock, Electrical, 233.

  Coal formation, theory of, 314.

  Cohesive force opposed to gravitation, 33.

  Cohesion and gravitation, 49.

  ---- distinguished from crystallization, 51.

  Cold, extreme, 110.

  Colour of bodies, 132.

  ---- changes of, in chemical combinations, 290.

  ---- blue, of sky, 320.

  ---- of steam, 321.

  Colours, Newton’s theory of, 135.

   heat rays, 85.

  Combining equivalents, 273.

  ---- forces, 292.

  Combination, laws of, 286.

  ---- of forces, 330.

  Combustion, 305.

  Comets, 26.

  Condensation of gases, 290.

  Conduction of heat, 69.

  Conducting power of bodies for heat, 89.

  Condition, change of chemical, 271.

  Conversion of motion, 16.

  Convection of heat, 69.

  Cotyledons, use of the, 368.

  Coulomb on repulsion of atoms, 47.

  Creation, oneness of, 406.

  Cretaceous formations, 344.

  Crosse on electricity, 227.

  Crustaceans, metamorphosis of, 389.

  Crust of the earth, 333.

  Crystals, pseudomorphous, 54.

  ----, size of, 56.

  Crystallogenic forces, 50.

  Crystalline bodies, magnetic influence of, 260.

  Cudworth’s “Plastic Nature,” 10.

  Current, electric, speed of, 231.

  ----, electricity, magnetic, 239.

  Crystallization, 50.

  Cultivation, limits of, 379.

  Currents of electricity around the earth, 224.

  Cyanite, a true magnet, 48.


  Daguerre’s discovery, 170.

  Daguerreotype, the, 172.

  Dalton on Aurora Borealis, 248.

  ---- on liquefaction, 287.

  Dalton’s atomic theory, 278.

  Daniel on incandescence, 100.

  Dark lines of spectrum, 125.

  Darwin on sea-weeds of the Southern Ocean, 316.

  Davy, Sir H., on the elements, 328.

  ---- on flame, 307.

  ---- discovers the alkaline metals, 325.

  Decomposition, electro-chemical, 208.

  De la Tour, Cagniard’s experiments, 105.

  Delaroche on heat, 93.

  Density of the earth, 31.

  Development, animal, 384.

  Dew, formation of, 81.

  Diamond, allotropic carbon, 43.

  ----, phosphorescence of, 160.

  Diamagnetism, 253.

  Diamagnetic nature of gases, 259.

  Diathermic bodies, 94.

  Diffusion of gases, 323.

  Digestion a cause of heat, 105.

  Dip of magnetic needle, 247.

  Dimorphism in crystals, 55.

  Directive power of a magnet on crystals, 261.

  Distribution of elements, 328.

  Divisibility of matter, 38.

  Döbereiner’s lamp, 281.

  Dispersion of light, 129.

  Draper on incandescence, 100.

  Dumas on atoms, 39.

  Dust, a grain of, 2.


  Earth, physical, the, 1.

  ---- density of, 31.

  ---- the revolution of the, 77.

  ----, geological formation of, 333.

  Earth’s, motion, 11.

  ---- temperature dependent on the sun, 63.

  Effects produced by loss of heat, 69.

  Eggs, number of, laid by insects, 399.

  Elective affinity, 292.

  Electricity, 193.

  Electricity and light influencing crystallization, 57.

  ----, kinds of, 195.

  ---- contained in water, 203.

  ---- developed by chemical action, 204.

  ----, velocity of, 231.

  ---- of plants, 380.

  Electric condition of matter, 5.

  ---- telegraph, the, 231.

  ---- affinity, 275.

  Electrical phosphorescence, 160.

  ---- action influenced by actinism, 183.

  ---- radiations, 190.

  ---- clock, 233.

  Electro-chemistry, 206.

  Electro culture, 223.

  Electrotype, the, 229.

  Electro-chemical decomposition, 208.

  Electro-magnetism, 240.

  Electrum, 193.

  Elements, chemical, 37, 272.

  ----, atmospheric, 325.

  ----, interchanges of, 319.

  Englefield on heat rays, 67.

  Eocene formations, 346.

  Equinoxes, precession of the, 244.

  ----, the vernal and autumnal, 77.

  Epicurus’ hooked atoms, 48.

  Epipolic phenomena, 129.

  Eremacausis, 105.

  Ether, hypothesis of an, 120.

  Examples of crystallization, 59.

  Expansion of bodies by heat, 96.

  Eye, mechanism of, 149.


  Faraday on Magnetism of Crystals, 59.

  ---- on solidification of gases, 112.

  ---- on magnetization of light, 147.

  ---- on the gymnotus, 211.

  ---- on diamagnetism, 254.

  Ferro-magnetic bodies, 255.

  Fish Lizard, the, 341.

  Fixed stars, light of, 122.

  Flint glass, permeability to heat, 65.

  Flora, fossil, 345.

  Flowers, influences of, 317.

  Fluid, magnetic theory of, 252.

  Fluorescence of light, 130.

  Forbes, Prof. Jas., on vibrations of heated metals, 97.

  Forbes, Prof. Edward, on zones of life in the ocean, 127.

  Forbes on colour of steam, 321.

  Force producing motion, 9.

  ---- a cause of motion, 17.

  ----, molecular, 40.

  ---- of crystallization, 61.

  Forces, active, in matter, 3.

  ----, balance of, 14.

  ---- in antagonism, 407.

  Form, change of, 2.

  ---- of surface, influence of, on climate, 351.

  ----, variety of vegetable, 359.

  Foster describes Northern Lights, 249.

  Fox, R. W., on temperature of Cornish mines, 91.

  Franklin on atoms, 47.

  Franklin’s kite experiment, 214.

  Freezing mixtures, 110.

  Freezing, remarkable phenomena of, 112.

  ---- of water, 302.

  Friction, 17.

  Frictional electricity, 199.

  Fraunhofer’s dark lines, 125.

  Franklin’s experiment on heat, 75.

  Fusion influenced by pressure, 107.


  Galvanism, 201.

  Galvani’s experiment, 201.

  Gases, condensation of, 111, 290.

  ----, magnetism of, 259.

  Gaseous constitution, 317.

  Gauss’s theory of magnetism, 243.

  Generation, spontaneous, 363.

  Geological phenomena, 332.

  Germ, Treviranus on the, 361.

  Germination of seeds, 367.

  Glass, , transparency to heat, 65.

  Goethe’s theory of colour, 139.

  Goethe on phosphorescence, 157.

  ---- on the leaf, 369.

  Graham’s law of diffusion, 323.

  Gravitation, 21.

  Growth explained, 52.

  ----, progress of, 364.

  ---- defined, 383.

  Grove decomposes water by heat, 98.

  Gulf stream, the, 81.

  Gulielmini on crystallisation, 50.

  Gun cotton, 103.

  Gymnotus electricus, 211.

  Gyroscope, the, 14.


  Hansteen and Arago on Northern Lights, 248.

  Hansteen on magnetism, 244.

  Heat, solar and terrestrial, 62.

  ----, conductors of, 90.

  ----, rays absorbed by atmosphere, 63, 73.

  ---- and light, their relations, 64.

  ----, radiation of, 82.

  ---- rays, , 85.

  ---- lessens chemical affinity, 88.

  ----, latent, 101.

  ----, decomposition by, 109, 276.

  ----, scientific knowledge of, 114.

  ---- developed by combustion of wood equivalent to heat absorbed in
      growth, 116.

  ----, influence of, on magnetism, 241.

  ----, action of, on water, 302.

  ----, influence of on plants, 371.

  ---- essential to life, 395.

  Heliography of M. Niepce, 170.

  Herbivorous animals, 315.

  Herschel on the nebulæ, 24.

  Herschel, Sir W., on heat rays, 67.

  Hobbes on the properties of matter, 8.

  Hopkins on the temperature of fusion, 107.

  Huyghens on double refraction, 140.

  Hydra, the, 387.

  Hydrogen, peroxide of, 298.

  ---- and oxygen, 289, 297.

  Hydro-carbons, 297.

  Hydro-carbon compounds, 308.

  Hypnotism, Mr. Braid on, 269.


  Ice, 301.

  Ichthyosaurus, the, 341.

  Igneous rocks, 335.

  Ignition by chemical action, 102.

  Iguanodon, the, 343.

  Incandescence, temperature of, 69-100.

  Influences of matter on heat, 79.

  Infusoria and animalculæ, 387.

  Interference of light, 138.

  Intensity, magnetic, 247.

  Invisible light, Moser on, 188.

  Iodide of silver found natural, 304.

  Iodine, 304.

  Iridescent paper, 137.

  Iron, magnetic, 235.

  ----, soft, rendered magnetic, 241.

  ----, rusting, 306.

  Isomeric compounds, 291.

  Isomorphism, 290.

  Isothermic lines, 92.

  Isodynamic lines, 247.


  Jones, Rymer, on sponges, 345.

  Joule on anhydrous salts, 287.

  ---- on heat and motion, 18.


  Kircher’s Magnetism, 264.

  Kupffar on magnetic storms, 249.


  Lamination of clay by electricity, 226.

  Land and sea, alternations of, 340.

  Laplace’s theory of the universe, 23.

  Latent heat, 101.

  Lavoisier’s theory of combustion, 305.

  Law of gravitation, 30.

  Lawson, letter from Mr., on germination of seeds, 375.

  Leaf, the functions of the, 369.

  Leaves of plants, action on air of, 311.

  Le Verrier on planet Neptune, 32.

  Leyden jar, the, 198.

  Lias formations, 341.

  Liebig and organic chemistry, 284.

  Life and light, 52.

  ----, influence of light on, 153.

  ---- dependent on light, 164.

  ----, vegetable, 362.

  ----, mysteries of, 398.

  Light, 118.

  ---- essential to life, 39.

  ---- of fixed stars, 122.

  ----, transparency to, 124.

  ----, transmission of, through different media, 128.

  ----, absorption of, 125.

  ----, interference of, 138.

  ----, polarized condition of, 141.

  ----, magnetization of, 146.

  ----, artificial, 162.

  ----, influence of, on plants, 373.

  ---- and heat, correlation of, 64.

  Lightning conductors, 215.

  Lindley on the leaf, 370.

  Lubbock, Sir J., on shooting stars, 22.

  Lodes, mineral, electricity of, 225.

  Luminous and actinic rays distinguished, 176.


  Machine electricity, 209.

  Magellanic clouds, 25.

  Magnetic curves, 236.

  ---- iron ore, 237.

  ---- polarity, 237.

  ---- points of convergence, 244.

  ---- poles of the earth, 245.

  ---- intensity, 247

  ---- storms, 249.

  ---- lines of no variation, 243.

  Magnetism, 235.

  ---- induced, 238.

  ---- influenced by heat, 242.

  ----, universality of, 253.

  ---- of gases, 259.

  ---- induced by solar rays 263.

  ---- and electricity, correlation of, 239.

  ---- and crystallisation, 57.

  Magneto-electrical decomposition, 230.

  Magnetisation of light, 146.

  Malus on polarisation, 139.

  Mammalia, fossil, 343.

  Man, temperature of, 105.

  Manganesiate of potash, 171.

  Mantell, Dr., on the iguanodon, 343.

  Mariotte on seat of vision, 149.

  Matter, its general conditions, 1.

  ----, forms of, 21.

  ----, transmutation of, 37.

  ----, divisibility of, 38.

  ----, solid, absorption of heat by, 75.

  ----, influence of, on light, 162.

  ----, polarity of, 265.

  ---- and its properties, 409.

  ----, entity of, 410.

  ----, varied condition of, 36.

  Mayer’s hypothesis of three colours, 138.

  Mechanical force and heat, 103.

  Mechanism of the eye, 149.

  Media, influence of, on light, 128.

  Medusæ, phosphorescence of, 159.

  Melloni on  heat rays, 85.

  ---- on new nomenclature for heat, 95.

  Mesmer and electricity, 222.

  Metamorphic rocks, 336.

  Metamorphoses of animals, 389.

  Mexico, Gulf of, warmth of the, 81.

  Mica, black, transparency to heat, 66.

  Miller, Dr., on dark lines of the spectrum, 126.

  Mineral veins, electricity of, 225.

  Mines, Cornish, temperature of, 91.

  Miocene formations, 346.

  Mirrors, magic, 191.

  Mitscherlich on expansion of crystals by heat, 257.

  Molecular forces, 35, 40.

  ----, compound action of, 279.

  Molecules, Dumas on, 39.

  ---- combination, 277.

  Morichini and Carpi on magnetism of violet rays of light, 263.

  Moser on invisible light, 189.

  Motion, 7.

  ---- a property of matter, 8.

  ----, principles of, 10.

  ---- of the earth, 12.

  ---- round an axis shows the earth’s motion, 18.

  ----, influence of, on form, 32.

  Mountain ranges probably determined by magnetic force, 262.

  Multiplication of life, 399.

  Musical notes produced by heat, 97.

  Muscular contraction by electricity, 202.

  Musschenbroek of Leyden, 198.

  Mythology, ancient, probable origin of, 353.


  Natural polarization, 145.

  Nebulous state of matter, 23.

  Neptune, discovery of, 32.

  Newton on gravitating force, 49.

  Newton on motion, 9.

  Newton’s hypothesis of matter, 4.

  ---- theory of heat, 115.

  ---- theory of light, 120.

  ---- theory of colours, 135.

  Niepce on the chemical radiations, 168.

  Nitrogen, magnetic neutrality of, 259.

  ----, combinations of, 324.

  ----, supposed metallic nature of, 325.

  Nocturnal radiation, 83.

  Northern lights, the, 268.


  Obsidian transparency to heat, 66.

  Ocean, waters of, 303.

  Oersted discovers electro-magnetism, 238.

  Orders of animals, 386.

  Organic creation, influence, 185.

  ---- compounds, 283.

  ---- compounds, influence of light on them, 181.

  ---- chemistry, 331.

  ---- cell, 360.

  ---- remains, 337.

  Organized forms, varieties of, 35.

  ---- bodies, heat of, 104.

  Organization, progress of, 385.

  Oxides, metallic, 326.

  Oxidizable metals, 305.

  Oxygen gas magnetic, 259.

  ---- and nitrogen, uses of, 321.

  ---- and carbon in animals, 396.

  Ozone, 299.

  ---- and electricity, 217.


  Palladium maintaining slow combustion, 309.

  Parathermic rays, 74.

  ---- rays, influence in nature, 377.

  Particles, Dumas on, 39.

  Peach on phosphorescence of the sea, 159.

  Pearsall on phosphorescence, 160.

  Pendulum, oscillation of, indicates the earth’s motion, 13.

  Perkins on repulsion of heat, 108.

  Permeation of heat, 96.

  Perturbations of Uranus, 31.

  Pestilential diseases, 216.

  Phenomena of vision, 148.

  ----, natural, of electricity, 194.

  ----, recent geological, 349.

  Phosphorescence of animals, 154.

  ---- of plants, 156.

  Phosphorescent spectrum, 184.

  Phosphoric acid detected in the oldest rocks, 337.

  Photosphere of the sun, 123.

  Photography, 170.

  ----, its importance, 180.

  Physiological influences of electricity, 219.

  Physical forces, action of, 4, 45.

  ---- forces, modes of motion, 7.

  ---- properties of polarized light, 142.

  Physiological influences of magnetism, 268.

  Pilchard, on the, by Couch, 315.

  Plants, distribution of, dependent on light, 133.

  ----, phosphorescence of, 156.

  ----, respiration of, 312.

  ---- and animals, dependence of, 313.

  ----, growth of, 368.

  ---- bend to the light, 373.

  ----, distribution of, 378.

  ---- of the Tropics, 381.

  Plane polarization, 141.

  “Plastic nature” of Cudworth, 10.

  Plateau’s experiment on bodies relieved from gravitation, 33.

  Platinum maintaining slow combustion, 309.

  Plato on motion, 10.

  ---- on light, 119.

  Plesiosaurus, the, 341.

  Pliocene formations, 346.

  Plücker on crystallo-magnetic force, 57.

  ---- on diamagnetic bodies, 256.

  Plumule, use of, 369.

  Plutonic rocks, 334.

  Polarization, circular and elliptical, 143.

  Polarization of light, 139.

  Polar condition of matter, 265.

  Polypes and infusoria, 387.

  Porosity of matter, 41.

  Porta, Baptista--camera obscura, 149.

  Powers, active, in nature, 405.

  Prevost, theory of, on heat, 96.

  Primary origin of our planet, 334.

  Principles of motion, 10.

  Prismatic refraction, 121.

  ---- rays, heat of, 67.

  ---- analysis of sunbeam, 134.

  Principle of gravitation, 29.

  ----, elementary, 38.

  Properties, essential, of matter, 5.

  Pseudomorphism, 54.

  Psychology of flowers, 357.

  Pterodactyl, the, 342.

  Pythagorean doctrine of motion, 10.


  Quinine, solution, influence of, on light, 129.


  Radiant heat, 69.

  Radiation and absorption of heat, 77.

  ----, nocturnal, 83.

  Raia torpedo, 211.

  Raymond, Du Bois, on animal electricity, 221.

  Refrangibility, rays of high, 130.

  ---- of solar forces, 168.

  Refraction, prismatic, 121.

  Races, dependence of, 315.

  Repulsion of heat, 108.

  Respiration of animals, 310.

  ---- plants, 312.

  Rest, absolute and relative, 15.

  Respiration a cause of heat, 105.

  Retina, the, 149.

  Revelations of nature, 401.

  Revolution of magnetic poles, 246.

  Robinson on decomposition by heat, 98.

  Rock formations, 335.

  Rocks, conducting power of, 224.

  Rosse’s, Lord, telescopes, 25.

  Rumford, Count, experiments on heat, 18.

  ---- on chemical properties of light, 99.

  Rings, Newton’s, 137.


  Safety lamp of Davy, 309.

  Salt rock, transparency to heat, 65.

  Saturn’s ring explained, 34.

  Savart on vibrating plates, 257.

  Seasons, influence of heat on the, 70.

  Sea, phosphorescence of, 158.

  Schönbein on ozone, 299.

  Schwabe on solar spots, 243.

  Seebeck on thermo-electricity, 211, 248.

  Selenite and alabaster, 60.

  Sénarmont on conducting power of crystals for heat, 257.

  Shooting stars, 21.

  Silicon, allotropic state of, 43.

  Silica, substitution of, 345.

  Simple bodies, chemical, 329.

  Sky of tropical climes, 319.

  Slow combustion in animals, 397.

  Smee on electricity and vitality, 219.

  Solar system, motion of, 11.

  ---- disc, light from, 185.

  ---- influence on magnetism, 263.

  Solidification of gases by Faraday, 112.

  Solstices, summer and winter, 77.

  Solar spots connected with magnetism, 243.

  Solar phosphori, 161.

  Somerville, Mrs., magnetises needles by light, 263.

  Sound and light, analogy of, 151.

  Spectra produced by polarization of light, 144.

  Spectrum, dark lines of, 125.

  Spheroidal condition of fluids, 107.

  Spontaneous ignition, 307.

  Stahl on phlogiston, 305.

  Stars, shooting, theories of, 21.

  Steel ornaments incandescent, 137.

  Stereoscope, the, 151.

  Stokes, Prof., on fluorescence, 130.

  Stratified formations, 334.

  Strength of animals, 400.

  Structure, influence of, on magnetism, 256.

  ----, relation of, to physical phenomena, 257.

  Struvé on motion of solar system, 12.

  Substitution, chemical, 279.

  ----, law of, 288.

  Substances, all, electric, 197.

  Subterranean temperature, 91.

  Sulphuric acid, permeability to heat, 65.

  Surfaces, action of, 282.

  Sulzar on galvanism, 201.

  Sulphuretted hydrogen, solid, 111.

  Sun, the central, 28.

  ----, the source of light, 121.

  ----, physical state of the, 123.

  ----, a magnetic centre, 265.


  Tadpole, metamorphosis of, 389.

  Talbot’s sensitive photographic process, 178.

  Telegraph, electric, 231.

  Temperature of incandescence, 68.

  Temperature, subterranean, 91.

  Terrestrial currents of electricity, 224.

  ---- magnetism, 255.

  Thales of Miletus discovers electricity, 193.

  Theories of light, 86, 118.

  Thermography, 188.

  Thermometric examination of the temperature of flowers, 76.

  Thermo-electricity, 209.

  Theory of motion producing force, 15.

  Thilorier on solid carbonic acid, 111.

  Time, influence of, 332.

  Tissues, catalytic power of, 310.

  Tourmaline, action of, on light, 142.

  Trade winds, 81.

  Transition series of rocks, 336.

  Transparency, calorific, 67.

  ----, luminous, 124.

  Transmutation of matter, 37.

  Transmission of light, 128.

  Transcalescent bodies, 94.

  Trevelyan, Mr., on vibration of heated metals, 97.

  Tyndale proves the influence of structure on magnetism, 258.

  Type, elements of the organic, 289.


  Undulations producing colour, 131.

  Undulatory theory of heat, 115.

  ---- theory of light, 121.

  Uranus, discovery of, 31.

  Uranium glass, influence of, on light, 129.


  Vapour, elastic force of, 318.

  Variation, magnetic, 244.

  Vegetables conductors of electricity, 379.

  Vegetable life, phenomena of, 357.

  Vegetation of carboniferous epoch, 339.

  Velocity of electricity, 231.

  Vertebrate animals, 390.

  Vision, phenomena of, 148.

  Vis vitæ, vital principle, 391.

  Vision single with a pair of eyes, 150.

  Vitality superior to physical force, 53.

  Vision, seat of, 149.

  Volume, doctrine of, 287.

  Volcanic action referred to chemical action, 271.

  Volatilization of matter, 27.

  Voltaic electricity, 201.


  Water, absorption of heat by, 74.

  ---- frozen free of air, 112.

  ---- free of air, peculiar state of, 113.

  ----, electricity in a drop of, 204.

  ----, composition of, 296.

  Wargentin’s notice of aurora, 248.

  Wave movement of heat and light, 68.

  Wealden formations, 343.

  Wedgwood on incandescence, 100.

  Wells, Dr., on dew, 84.

  Wiedemann on electrical vibrations, 257.

  Wenzel’s proportional numbers, 277.

  Winds dependent on heat, 80.

  Wollaston notices dark lines in spectrum, 125.

  World, its age, 404.


  Young on molecular forces, 49.


  Zodiacal light, 25.

  Zoophytes, microscopic, 387.


THE END.


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TRANSCRIBER’S NOTE.


Archaic, obsolete, unusual and inconsistent spellings have been
maintained as in the original book. Obvious errors have been fixed as
detailed below.

Some entries in the index were out of alphabetical order in the
original book. They have been moved without noting them in the details
below.

The totals in the various tables are not equal to the sum of the column
above them. I assume this is due to round off error, or details in the
original data which are not represented here. No attempt has been made
to correct these totals.

In the original book, half of the publisher’s catalogue (Bohn’s Books)
was in the beginnig of the book. It was moved to immediately precede
the other half of the catalogue at the end of the book.

Preface, Contents, Introduction, Index, Bohn’s Books and Transcriber’s
Note have been added to the table of contents. Only the chapters of
the book were in the table of contents in the original book. The title
"Bohn’s Books" was inserted into the beginning of the publisher’s book
catalogue.

In the table below, the first line shows the text in this ebook, the
second line shows the text in the original book.

  Page vii.:  conditions of Matter--Diamagnetism, &c.    235
  Originally: conditions of Matter--Dia-Magnetism, &c.    235

  Page viii.: Time, an element in Nature’s Operations--Geological
  Originally: Time, an element in Nature’s Operations==Geological

  Page viii.: Progress of Matter towards Organization
  Originally: Progress of Matter rowards Organization

  Page xii.:  of external nature, evoked beautiful spiritualizations
  Originally: of external nature, evoked beautiful spirtualizations

  Footnote 1: Boscovich regarded the constitution of matter differently
  Originally: Boscovitch regarded the constitution of matter differently

  Footnote 1: full explanation of the theory of Boscovich.)
  Originally: full explanation of the theory of Boscovitch.)

  Page 8:     The views of metaphysicians regarding motion involve
  Originally: The views of metaphyscians regarding motion involve

  Page 14:    tremulous gyration upon the deck of a vast aërial ship
  Originally: tremulous gyration upon the deck of a vast aerial ship

  Page 27:    agent of organisation and all manifestations of beauty?
  Originally: agent of organisation and all manifestatious of beauty?

  Footnote 18: fixes, est déterminée par ce qui précède entre certaines
  Originally:  fixes, est determinée par ce qui précède entre certaines

  Footnote 18: est le groupe central de l’ensemble du système
  Originally:  est le groupe central l’ensemble du système

  Footnote 24: into a single mass at the bottom of the flask under
  Originally:  into a single mass at the bottom of the flask unde

  Page 42:    with which the particles combined, from interstices,
  Originally: with which the particles combined, from insterstices,

  Page 45:    bromine, &c., are the results of different _allotropic_
  Originally: bromime, &c., are the results of different _allotropic_

  Page 46:    which,--from the imperfections of science,--resisting
  Originally: which,--from the imperfectious of science,--resisting

  Page 46:    The experiments of Faraday and of Plücker prove
  Originally: The experiments of Faraday and of Plucker prove

  Footnote 25: Young’s _Natural Philosophy_; ed. by Rev. P. Kelland.
  Originally:  Young’s _Natural Philosophy_; ed. by Rev. P. Lelland.

  Footnote 35: Hence the origin of compound and visible bodies; hence
  Originally:  Hence the origin of compouud and visible bodies; hence

  Page 50:    her operations, but the very processes themselves.
  Originally: her operations, but the very processes themselvss.

  Paqe 59:    combination appears to the eye in no respect different
  Originally: combinatiou appears to the eye in no respect different

  Page 61:    Those fissures formed by the first system of crystalline
  Originally: Those fissures formed by the first sytsem of crystalline

  Page 68:    luminous power are sufficiently striking to convince us
  Originally: luminous power are sufficienlty striking to convince us

  Page 109:   of temperature is experienced.[79] Professor Plücker, of
  Originally: of temperature is experienced.[79] Professor Plucker, of

  Footnote 55: this motion. He was followed by Musschenbroek, and then
  Originally:  this motion. He was followed by Muschenbroek, and then

  Footnote 61: _regarding the internal temperature of the Earth_: by
  Originally:  _regarding the internal temperature of tha Earth_: by

  Footnote 78: _en vertu de l’état sphéroïdal dans un creuset_
  Originally:  _en vertu de l’état sphérodïal dans un creuset_

  Page 121:   Fraunhofer, Herschel, Brewster, and others, but proceed
  Originally: Frauenhofer, Herschel, Brewster, and others, but proceed

  Page 123:   between charcoal points at the poles of a powerful voltaic
  Originally: between charcoal points a the poles of a powerful voltaic

  Page 129:   of quinine, and the fluor spar, we obtain the same results
  Originally: of quinine, and the flour spar, we obtain the same results

  Page 140:   the first instance, by Erasmus Bartholin, in Iceland-spar,
  Originally: the first instance, by Erasmus Bartolin, in Iceland-spar,

  Page 145:   from what has been already stated, that some
  Originally: from what has beeen already stated, that some

  Page 153:   to prove that light is absolutely necessary to
  Originally: to prove that light is absolutely neccessary to

  Page 159:   of light behind them.[113] By microscopic examination
  Originally: of light behind them.[113] By miscroscopic examination

  Page 159:   Benvenuto Cellini gave a curious account of a carbuncle
  Originally: Benvenuto Cellini give a curious account of a carbuncle

  Page 160:   near a fire. From this it may be inferred that the
  Originally: near a a fire. From this it may be infered that the

  Footnote 88: Brande’s _Manual of Chemistry_; or, indeed, any work
  Originally:  Brande’s _Mannal of Chemistry_; or, indeed, any work

  Footnote 94: Schouw, _Grundzüge der Pflanzengeographie_. Also his
  Originally:  Schouw, _Grundüzge der Pflanzengeographie_. Also his

  Footnote 95: Fraunhofer’s measure of illuminating power is as
  Originally:  Frauenhofer’s measure of illuminating power is as

  Footnote 99: _Sur une Propriété de la Lumière Réfléchie_: Mémoires
  Originally:  _Sur une Propriété de la Lumière Réfléchie_: Memoires

  Page 176:   the strongest sunlight which has passed through
  Originally: the strongest sun-light which has passed through

  Page 179:   productions of the photographer as on those of the
  Originally: productions of the photograper as on those of the

  Page 180:   preserve the lineaments of those who have benefited
  Originally: preserve the lineaments of those who have benefitted

  Page 185:   line, over which no action takes place, is preserved at
  Originally: line, over which no action takes plates, is preserved at

  Page 185:   presented to us by a circular body: calorific action seems
  Originally: present to us by a circular body: calorific action seems

  Page 188:   piece of wood is used instead of a metal, there will, by
  Originally: piece of wood is used instead of a medal, there will, by

  Footnote 126: _dans la végétation_: by Senebier; Genève et Paris, 1788
  Originally:   _dans la végetation_: by Senebier; Genève et Paris, 1788

  Page 198:   Leyden phial,--so called from its inventor, Musschenbroek,
  Originally: Leyden phial,--so called from its inventor, Muschenbrock,

  Page 219:   may be made a measurer of nervous irritability.[154] There
  Originally: may be made a measurer of nervous iritability.[154] There

  Footnote 141: _Traité Expérimental de l’Électricité et du Magnétisme_:
  Originally:   _Traité Expérimental de l’Electricité et du Magnétisme_:

  Footnote 146: _Traité Expérimental de l’Électricité et du Magnétisme_.
  Originally:   _Traité Expérimental de l’Electricité et du Magnétisme_

  Footnote 160: where the cobalt was discovered between two portions of
  Originally:   where the cobalt was discovered betweed two portions of

  Page 235:   Storms--Magnetic conditions of Matter--Diamagnetism,
  Originally: Storms--Magnetic conditions of Matter--Dia-Magnetism,

  Page 236:   Magnêtum, quia sit patriis in finibus ortus.
  Originally: Magnêtum, buia sit patriis in finibus ortus.

  Page 251:   conditions of change in this our earth: an element to
  Originally: conditions of change in this our earth: an elemeut to

  Page 257:   Wiedemann, by employing a fine point through which
  Originally: Wiedmann, by employing a fine point through which

  Page 258:   than in any other. M. Wiedemann comes to the conclusion
  Originally: than in any other. M. Wiedmann comes to the conclusion

  Page 260:   salt, the protosulphate, ordinarily crystallizes so that
  Originally: salt, the proto-sulphate, ordinarily crystallizes so that

  Footnote 176: Humboldt: _Exposé des Variations Magnétiques_.
  Originally:   Humboldt: _Exposé des Variations Magnetiques_.

  Footnote 188: _Electro-Magnetic Influence_, by Professor Zantedeschi.
  Originally:   _Electro-Magnetic Influence_, by Professor Zandeteschi.

  Footnote 190: detailed account of the experiments of Faraday, Plücker,
  Originally:   detailed account of the experiments of Faraday, Plucker,

  Page 276:   light determine these changes? It is evident, although
  Originally: light determine these change? It is evident, although

  Page 281:   chemical change. Döbereiner next discovered that
  Originally: chemical change. Dœbereiner next discovered that

  Page 282:   a fearful example in the progress of Asiatic
  Originally: a fearful example in the progress of Asatic

  Page 300:   as being either peroxide of hydrogen, or an allotropic
  Originally: as being either per-oxide of hydrogen, or an allotropic

  Page 304:   the gas which we employ so advantageously for illumination
  Originally: the gas which we emply so advantageously for illumination

  Page 306:   increasing,--true combustion takes place. In this way
  Originally: increasing,--true combustion takes plaee. In this way

  Page 306:   sawdust, &c., frequently ignite; and to such an
  Originally: saw-dust, &c., frequently ignite; and to such an

  Page 316:   Mr. Darwin remarks, that if the immense sea-weeds of
  Originally: Mr. Darwin remarks, that if the immense seaweeds of

  Page 317:   When Shakespeare made his charming Ariel sing--
  Originally: When Shakspeare made his charming Ariel sing--

  Footnote 212: (Redundant line removed before item 2 in table.)
  Originally: According to one view,      | According to the other view,

  Page 334:   speculation, which may have occasional marks of ingenuity,
  Originally: speculation, whieh may have occasional marks of ingenuity,

  Page 337:   origin, the rational inference is against the speculation;
  Originally: orgin, the rational inference is against the speculation;

  Page 370:   capsule of _nigella orientalis_ consists of pods assembled
  Originally: capsule of _nigilla orientalis_ consists of pods assembled

  Page 370:   a centre, and partially united; in _nigella damascena_
  Originally: a centre, and partially united; in _nigilla damascena_

  Page 399:   whose minds are sceptical upon any development of the
  Originally: whose mind are sceptical upon any development of the

  Page 406:   evidence of a beautiful adjustment of the balance of
  Originally: evidence of a beautifnl adjustment of the balance of

  Page 408:   Let but a slight disturbance occasion a vibration
  Originally: Let but a slight disturbance occcasion a vibration

  Page 409:   A cheerless philosophy, derived from the transcendentalism
  Originally: A cheerless philosophy, derived from the transendentalism

  Page 410:   which are allowed the privilege of tracing out its
  Originally: which are alowed the privilege of tracing out its

  Page 413:   Aëreal currents dependent on heat, 80.
  Originally: Æreal currents dependent on heat, 80.

  Page 413:   Animal electricity, 211, 392.
  Originally: Magnetic electricity, 211, 392.

  Page 413:   Bartholin on Iceland spar, 140.
  Originally: Bartolin on Iceland spar, 140.

  Page 414:   Cagniard de la Tour state, 106.
  Originally: Caignard de la Tour state, 106.

  Page 415:   Döbereiner’s lamp, 281.
  Originally: Doebereiner’s lamp, 281.

  Page 415:   Eye, mechanism of, 149.
  Originally: Eye, mechanism of, 491.

  Page 416:   ---- on diamagnetism, 254.
  Originally: ---- on dia-magnetism, 254.

  Page 418:   Musschenbroek of Leyden, 198.
  Originally: Muschenbrock of Leyden, 198.

  Page 421:   Wiedemann on electrical vibrations, 257.
  Originally: Wiedman on electrical vibrations, 257.

  Bohn’s Books: =LOUDON’S (MRS.) ENTERTAINING NATURALIST=,
  Originally:   =LOUDON’S (MRS.) ENTERTAING NATURALIST=,

  Bohn’s Books: Indexes of Scientific and Popular Names. _With_
  Originally:   Indexes of Scientific and and Popular Names. _With_

  Bohn’s Books: =18. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus,
  Originally:   =8. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus,

  Bohn’s Books: =35. JUVENAL, PERSIUS, &c.= By the REV. L. EVANS, M.A.
  Originally:   =34. JUVENAL, PERSIUS, &c.= By the REV. L. EVANS, M.A.





End of the Project Gutenberg EBook of The Poetry of Science or, Studies of
the Physical Phenomena of Nature, by Robert Hunt

*** 