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                             THE LETTER OF
                                 PETRUS
                               PEREGRINUS
                        ON THE MAGNET, A.D. 1269


                             TRANSLATED BY
                         BROTHER ARNOLD, M.Sc.
                 PRINCIPAL OF LA SALLE INSTITUTE, TROY
                                  WITH
                          INTRODUCTORY NOTICE
                                   BY
                        BROTHER POTAMIAN, D.Sc.
                   PROFESSOR OF PHYSICS IN MANHATTAN
                           COLLEGE, NEW YORK


                                NEW YORK
                       McGRAW PUBLISHING COMPANY
                                 MCMIV

                          Copyright, 1904, by
                       McGraw Publishing Company




                              INTRODUCTORY


The magnetic lore of classic antiquity was scanty indeed, being limited
to the attraction which the lodestone manifests for iron. Lucretius
(99-55 B. C.), however, in his poetical dissertation on the magnet,
contained in _De Rerum Natura_, Book VI.[1] recognizes magnetic
repulsion, magnetic induction, and to some extent the magnetic field
with its lines of force, for in verse 1040 he writes:

  Oft from the magnet, too, the steel recedes,
  Repelled by turns and re-attracted close.

And in verse 1085:

  Its viewless, potent virtues men surprise;
  Its strange effects, they view with wond’ring eyes
  When without aid of hinges, links or springs
  A pendant chain we hold of steely rings
  Dropt from the stone—the stone the binding source—
  Ring cleaves to ring and owns magnetic force:
  Those held above, the ones below maintain,
  Circle ’neath circle downward draws in vain
  Whilst free in air disports the oscillating chain.

The poet Claudian (365-408 A. D.) wrote a short idyll on the attractive
virtue of the lodestone and its symbolism; St. Augustine (354-430), in
his work _De Civitate Dei_, records the fact that a lodestone, held
under a silver plate, draws after it a scrap of iron lying on the plate.
Abbot Neckam, the Augustinian (1157-1217), distinguishes between the
properties of the two ends of the lodestone, and gives in his _De
Utensilibus_, what is perhaps the earliest reference to the mariner’s
compass that we have. Albertus Magnus, the Dominican (1193-1280), in his
treatise, _De Mineralibus_, enumerates different kinds of natural
magnets and states some of the properties commonly attributed to them;
the minstrel, Guyot de Provins, in a famous satirical poem, written
about 1208, refers to the directive quality of the lodestone and its use
in navigation, as do also Cardinal de Vitry in his _Historia Orientalis_
(1215-1220); Brunetto Latini, poet, orator and philosopher, in his
_Trésor des Sciences_, a veritable library, written in Paris in 1260;
Raymond Lully, the Enlightened Doctor, in his treatise, _De
Contemplatione_, begun in 1272, and Guido Guinicelli, the poet-priest of
Bologna, who died in 1276.

The authors of these learned works were too busy with the pen to find
time to devote to the close and prolonged study of natural phenomena
necessary for fruitful discovery, and so had to content themselves with
recording and discussing in their tomes the scientific knowledge of
their age without making any notable additions to it.

But this was not the case with such contemporaries of theirs as Roger
Bacon, the Franciscan, and his Gallic friend, Pierre de Maricourt,
commonly called Petrus Peregrinus, the subject of the present notice, a
man of academic culture and of a practical rather than speculative turn
of mind. Of the early years of Peregrinus nothing is known save that he
studied probably at the University of Paris, and that he graduated with
the highest scholastic honors. He owes his surname to the village of
Maricourt, in Picardy, and the appellation Peregrinus, or Pilgrim, to
his having visited the Holy Land as a member of one of the crusading
expeditions of the time.

In 1269 we find him in the engineering corps of the French army then
besieging Lucera, in Southern Italy, which had revolted from the
authority of its French master, Charles of Anjou. To Peregrinus was
assigned the work of fortifying the camp and laying mines as well as of
constructing engines for projecting stones and fire-balls into the
beleaguered city.

It was in the midst of such warlike preoccupations that the idea seems
to have occurred to him of devising a piece of mechanism to keep the
astronomical sphere of Archimedes in uniform rotation for a definite
time. In the course of his work over the new motor, Peregrinus was
gradually led to consider the more fascinating problem of perpetual
motion itself with the result that he showed, at least diagrammatically,
and to his own evident satisfaction, how a wheel might be driven round
forever by the power of magnetic attraction.

Elated over his imaginary success, Peregrinus hastened to inform a
friend of his at home; and that his friend might the more readily
comprehend the mechanism of the motor and the functions of its parts, he
proceeds to set forth in a methodical manner all the properties of the
lodestone, most of which he himself had discovered. It is a fortunate
circumstance that this Picard friend of his was not a man learned in the
sciences, otherwise we would probably never have had the remarkable
exposition which Peregrinus gives of the phenomena and laws of
magnetism. This letter of 3,500 words is the first great landmark in the
domain of magnetic philosophy, the next being Gilbert’s _De Magnete_, in
1600.

The letter was addressed from the trenches at Lucera, Southern Italy, in
August, 1269, to Sigerus de Foucaucourt, his “amicorum intimus,” the
dearest of friends. A more enlightened friend, however, than the knight
of Foucaucourt was Roger Bacon, who held Peregrinus in the very highest
esteem, as the following glowing testimony shows: “There are but two
perfect mathematicians,” wrote the English monk, “John of London and
Petrus de Maharne-Curia, a Picard.” Further on in his _Opus Tertium_,
Bacon thus appraises the merits of the Picard: “I know of only one
person who deserves praise for his work in experimental philosophy, for
he does not care for the discourses of men and their wordy warfare, but
quietly and diligently pursues the works of wisdom. Therefore, what
others grope after blindly, as bats in the evening twilight, this man
contemplates in all their brilliancy because he is a master of
experiment. Hence, he knows all natural science whether pertaining to
medicine and alchemy, or to matters celestial and terrestrial. He has
worked diligently in the smelting of ores as also in the working of
minerals; he is thoroughly acquainted with all sorts of arms and
implements used in military service and in hunting, besides which he is
skilled in agriculture and in the measurement of lands. It is impossible
to write a useful or correct treatise in experimental philosophy without
mentioning this man’s name. Moreover, he pursues knowledge for its own
sake; for if he wished to obtain royal favor, he could easily find
sovereigns who would honor and enrich him.”

This last statement is worthy of the best utterances of the twentieth
century. Say what they will, the most ardent pleaders of our day for
original work and laboratory methods cannot surpass the Franciscan monk
of the thirteenth century in his denunciation of mere book learning or
in his advocacy of experiment and research, while in Peregrinus, the
mediævalist, they have Bacon’s impersonation of what a student of
science ought to be. Peregrinus was a hard worker, nor a mere theorizer,
preferring, Procrustean-like, to make theory fit the facts rather than
facts the theory; he was a brilliant discoverer who knew at the same
time how to use his discoveries for the benefit of mankind; he was a
pioneer of science and a leader in the progress of the world.

An analysis of the “Epistola” shows that

(_a_) Peregrinus was the first to assign a definite position to the
poles of a lodestone, and to give directions for determining which is
north and which south;

(_b_) He proved that unlike poles attract each other, and that similar
ones repel;

(_c_) He established by experiment that every fragment of a lodestone,
however small, is a complete magnet, thus anticipating one of our
fundamental laboratory illustrations of the molecular theory;

(_d_) He recognized that a pole of a magnet may neutralize a weaker one
of the same name, and even reverse its polarity;

(_e_) He was the first to pivot a magnetized needle and surround it with
a graduated circle, Figs. 2 and 3.[2]

(_f_) He determined the position of an object by its magnetic bearing as
done to-day in compass surveying; and

(_g_) He introduced into his perpetual motion machine, Fig. 4, the idea
of a magnetic motor, a clever idea, indeed, for a thirteenth century
engineer.

This rapid summary will serve to show that the letter of Peregrinus is
one of great interest in physics as well as in navigation and geodesy.
For nearly three centuries, it lay unnoticed among the libraries of
Europe, but it did not escape Gilbert, who makes frequent mention of it
in his _De Magnete_, 1600; nor the illustrious Jesuit writers, Cabæus,
who refers to it in his _Philosophia Magnetica_, 1629, and Kircher, who
quotes from it in his _De Arte Magnetica_, 1641; it was well known to
Jean Taisnier, the Belgian plagiarist, who transferred a great part of
it verbatim to the pages of his _De Natura Magnetis_, 1562, without a
word of acknowledgment. By this piece of fraud, Taisnier acquired
considerable celebrity, a fact that goes to show the meritorious
character of the work which he unscrupulously copied.

This memorable letter is divided into two parts: the first contains ten
chapters on the general properties of the lodestone; the second has but
three chapters, and shows how the author proposed to use a lodestone for
the purpose of producing continuous rotation.

There are many manuscript copies of the letter in European libraries:
the Bodleian has six; the Vatican, two; Trinity College, Dublin, one;
the Bibliothèque Nationale, Paris, one; Leyden, Geneva and Turin, one
each. The Leyden MS. has acquired special notoriety from a passage which
appears near the end of it in which reference is made to magnetic
declination and its value given: but Prof. W. Wenckebach, of The Hague,
has shown[3] that the lines are spurious, having been interpolated in
the manuscript in the early part of the sixteenth century.

The Leyden manuscript has also led some writers to believe in a
fictitious author of the letter, one Peter Adsiger, or Petrus Adsigerus.
As said above, Sigerus was the name of his countryman, to whom
Peregrinus addressed his letter, the _Epistola ad Sigerum_, from the
trenches at Lucera, in August, 1269.

Magnetic declination was unknown to Peregrinus, else he would not have
written the following words: “Wherever a man may be, he finds the
lodestone pointing to the heavens in accordance with the position of the
meridian” (Chapter X). Of course, the geographical meridian is the one
here meant, as the necessity of a distinct magnetic meridian had not yet
occurred to any one.

Nor was this important magnetic element known to Columbus when he sailed
from the shores of the Old World in 1492 as appears from the surprise
with which he noticed the deviation of the needle from North as well as
from the consternation of his pilots. Columbus has the unquestionable
merit of being the first to observe and record the change of declination
with change of place.

The first printed edition of the Epistola, now very rare, was prepared
by Achilles Gasser, a physician of Lindau, a man well versed in
mathematics, astronomy, history and philosophy. The work was printed in
Augsburg in 1558. A copy of this early print is among the treasures of
the Wheeler collection in the library of the American Institute of
Electrical Engineers, New York. It was from this text that the
translation which follows was made.

Besides the Latin edition of Gasser, 1558, there is also that of Libri
in his _Histoire des Sciences Mathématiques_, 1838; of Bertelli, 1868,
and Hellmann, 1898. Bertelli’s is a learned and exhaustive work in which
the Barnabite monk, sometimes called by mistake, Barnabita, instead of
Bertelli, collates and compares the readings of the two Vatican codices
with other texts, adding copious references and explanatory notes. It
appeared in the _Bulletino di Bibliografia e di Storia delle Scienze
Matematiche e Fisiche_ for 1868.

Of translations, we have that which Richard Eden made from Taisnier’s
pirated extracts, the first dated edition appearing in 1579. Cavallo’s
_Treatise on Magnetism_, 1800, also contains some of the more remarkable
passages. The only complete English translation that we have, appeared
in 1902 from the scholarly pen of Prof. Silvanus P. Thompson, of London.
It is an _édition de luxe_ beautifully rubricated, but limited to 250
copies. The translation was based on the texts of Gasser and Hellmann,
amended by reference to a manuscript in the author’s possession, dated
1391. We are informed that Mr. Fleury P. Mottelay, of New York, the
learned translator of Gilbert’s _De Magnete_, possesses a manuscript
version by Prof. Peirce, of Harvard, of the Paris codex, of which he
made a careful study in an endeavor to decipher the illegible parts.




                                 PART I




                             THE LETTER OF
                               PEREGRINUS


                                 PART I
                               CHAPTER I
                          PURPOSE OF THIS WORK

Dearest of Friends:

At your earnest request, I will now make known to you, in an unpolished
narrative, the undoubted though hidden virtue of the lodestone,
concerning which philosophers up to the present time give us no
information, because it is characteristic of good things to be hidden in
darkness until they are brought to light by application to public
utility. Out of affection for you, I will write in a simple style about
things entirely unknown to the ordinary individual. Nevertheless I will
speak only of the manifest properties of the lodestone, because this
tract will form part of a work on the construction of philosophical
instruments. The disclosing of the hidden properties of this stone is
like the art of the sculptor by which he brings figures and seals into
existence. Although I may call the matters about which you inquire
evident and of inestimable value, they are considered by common folk to
be illusions and mere creations of the imagination. But the things that
are hidden from the multitude will become clear to astrologers and
students of nature, and will constitute their delight, as they will also
be of great help to those that are old and more learned.


                               CHAPTER II
                   QUALIFICATIONS OF THE EXPERIMENTER

You must know, my dear friend, that whoever wishes to experiment, should
be acquainted with the nature of things, and should not be ignorant of
the motion of the celestial bodies. He must also be skilful in
manipulation in order that, by means of this stone, he may produce these
marvelous effects. Through his own industry he can, to some extent,
indeed, correct the errors that a mathematician would inevitably make if
he were lacking in dexterity. Besides, in such occult experimentation,
great skill is required, for very frequently without it the desired
result cannot be obtained, because there are many things in the domain
of reason which demand this manual dexterity.


                              CHAPTER III
                  CHARACTERISTICS OF A GOOD LODESTONE

The lodestone selected must be distinguished by four marks—its color,
homogeneity, weight and strength. Its color should be iron-like, pale,
slightly bluish or indigo, just as polished iron becomes when exposed to
the corroding atmosphere. I have never yet seen a stone of such
description which did not produce wonderful effects. Such stones are
found most frequently in northern countries, as is attested by sailors
who frequent places on the northern seas, notably in Normandy, Flanders
and Picardy. This stone should also be of homogeneous material; one
having reddish spots and small holes in it should not be chosen; yet a
lodestone is hardly ever found entirely free from such blemishes. On
account of uniformity in its composition and the compactness of its
innermost parts, such a stone is heavy and therefore more valuable. Its
strength is known by its vigorous attraction for a large mass of iron;
further on I will explain the nature of this attraction. If you chance
to see a stone with all these characteristics, secure it if you can.


                               CHAPTER IV
              HOW TO DISTINGUISH THE POLES OF A LODESTONE

I wish to inform you that this stone bears in itself the likeness of the
heavens, as I will now clearly demonstrate. There are in the heavens two
points more important than all others, because on them, as on pivots,
the celestial sphere revolves: these points are called, one the arctic
or north pole, the other the antarctic or south pole. Similarly you must
fully realize that in this stone there are two points styled
respectively the north pole and the south pole. If you are very careful,
you can discover these two points in a general way. One method for doing
so is the following: With an instrument with which crystals and other
stones are rounded let a lodestone be made into a globe and then
polished. A needle or an elongated piece of iron is then placed on top
of the lodestone and a line is drawn in the direction of the needle or
iron, thus dividing the stone into two equal parts. The needle is next
placed on another part of the stone and a second median line drawn. If
desired, this operation may be performed on many different parts, and
undoubtedly all these lines will meet in two points just as all meridian
or azimuth circles meet in the two opposite poles of the globe. One of
these is the north pole, the other the south pole. Proof of this will be
found in a subsequent chapter of this tract.

A second method for determining these important points is this: Note the
place on the above-mentioned spherical lodestone where the point of the
needle clings most frequently and most strongly; for this will be one of
the poles as discovered by the previous method. In order to determine
this point exactly, break off a small piece of the needle or iron so as
to obtain a fragment about the length of two fingernails; then put it on
the spot which was found to be the pole by the former operation. If the
fragment stands perpendicular to the stone, then that is,
unquestionably, the pole sought; if not, then move the iron fragment
about until it becomes so; mark this point carefully; on the opposite
end another point may be found in a similar manner. If all this has been
done rightly, and if the stone is homogeneous throughout and a choice
specimen, these two points will be diametrically opposite, like the
poles of a sphere.


                               CHAPTER V
HOW TO DISCOVER THE POLES OF A LODESTONE AND HOW TO TELL WHICH IS NORTH
                            AND WHICH SOUTH

The poles of a lodestone having been located in a general way, you will
determine which is north and which south in the following manner: Take a
wooden vessel rounded like a platter or dish, and in it place the stone
in such a way that the two poles will be equidistant from the edge of
the vessel; then place the dish in another and larger vessel full of
water, so that the stone in the first-mentioned dish may be like a
sailor in a boat. The second vessel should be of considerable size so
that the first may resemble a ship floating in a river or on the sea. I
insist upon the larger size of the second vessel in order that the
natural tendency of the lodestone may not be impeded by contact of one
vessel against the sides of the other. When the stone has been thus
placed, it will turn the dish round until the north pole lies in the
direction of the north pole of the heavens, and the south pole of the
stone points to the south pole of the heavens. Even if the stone be
moved a thousand times away from its position, it will return thereto a
thousand times, as by natural instinct. Since the north and south parts
of the heavens are known, these same points will then be easily
recognized in the stone because each part of the lodestone will turn to
the corresponding one of the heavens.


                               CHAPTER VI
                   HOW ONE LODESTONE ATTRACTS ANOTHER

When you have discovered the north and the south pole in your lodestone,
mark them both carefully, so that by means of these indentations they
may be distinguished whenever necessary. Should you wish to see how one
lodestone attracts another, then, with two lodestones selected and
prepared as mentioned in the preceding chapter, proceed as follows:
Place one in its dish that it may float about as a sailor in a skiff,
and let its poles which have already been determined be equidistant from
the horizon, i. e., from the edge of the vessel. Taking the other stone
in your hand, approach its north pole to the south pole of the lodestone
floating in the vessel; the latter will follow the stone in your hand as
if longing to cling to it. If, conversely, you bring the south end of
the lodestone in your hand toward the north end of the floating
lodestone, the same phenomenon will occur; namely, the floating
lodestone will follow the one in your hand. Know then that this is the
law: the north pole of one lodestone attracts the south pole of another,
while the south pole attracts the north. Should you proceed otherwise
and bring the north pole of one near the north pole of another, the one
you hold in your hand will seem to put the floating one to flight. If
the south pole of one is brought near the south pole of another, the
same will happen. This is because the north pole of one seeks the south
pole of the other, and therefore repels the north pole. A proof of this
is that finally the north pole becomes united with the south pole.
Likewise if the south pole is stretched out towards the south pole of
the floating lodestone, you will observe the latter to be repelled,
which does not occur, as said before, when the north pole is extended
towards the south. Hence the silliness of certain persons is manifest,
who claim that just as scammony attracts jaundice on account of a
similarity between them, so one lodestone attracts another even more
strongly than it does iron, a fact which they suppose to be false
although really true as shown by experiment.


                              CHAPTER VII
  HOW IRON TOUCHED BY A LODESTONE TURNS TOWARDS THE POLES OF THE WORLD

It is well known to all who have made the experiment, that when an
elongated piece of iron has touched a lodestone and is then fastened to
a light block of wood or to a straw and made float on water, one end
will turn to the star which has been called the Sailor’s star because it
is near the pole; the truth is, however, that it does not point to the
star but to the pole itself. A proof of this will be furnished in a
following chapter. The other end of the iron will point in an opposite
direction. But as to which end of the iron will turn towards the north
and which to the south, you will observe that that part of the iron
which has touched the south pole of the lodestone will point to the
north and conversely, that part which had been in contact with the north
pole will turn to the south. Though this appears marvelous to the
uninitiated, yet it is known with certainty to those who have tried the
experiment.


                              CHAPTER VIII
                     HOW A LODESTONE ATTRACTS IRON

If you wish the stone, according to its natural desire, to attract iron,
proceed as follows: Mark the north end of the iron and towards this end
approach the south pole of the stone, when it will be found to follow
the latter. Or, on the contrary, to the south part of the iron present
the north pole of the stone and the latter will attract it without any
difficulty. Should you, however, do the opposite, namely, if you bring
the north end of the stone towards the north pole of the iron, you will
notice the iron turn round until its south pole unites with the north
end of the lodestone. The same thing will occur when the south end of
the lodestone is brought near the south pole of the iron. Should force
be exerted at either pole, so that when the south pole of the iron is
made touch the south end of the stone, then the virtue in the iron will
be easily altered in such a manner that what was before the south end
will now become the north and conversely. The cause is that the last
impression acts, confounds, or counteracts and alters the force of the
original movement.


                               CHAPTER IX
 WHY THE NORTH POLE OF ONE LODESTONE ATTRACTS THE SOUTH POLE OF ANOTHER
                             AND VICE VERSA

As already stated, the north pole of one lodestone attracts the south
pole of another and conversely; in this case the virtue of the stronger
becomes active, whilst that of the weaker becomes obedient or passive. I
consider the following to be the cause of this phenomenon: the active
agent requires a passive subject, not merely to be joined to it, but
also to be united with it, so that the two make but one by nature. In
the case of this wonderful lodestone this may be shown in the following
manner: Take a lodestone which you may call _A D_, in which _A_ is the
north pole and _D_ the south; cut this stone into two parts, so that you
may have two distinct stones; place the stone having the pole _A_ so
that it may float on water and you will observe that _A_ turns towards
the north as before; the breaking did not destroy the properties of the
parts of the stone, since it is homogeneous; hence it follows that the
part of the stone at the point of fracture, which may be marked _B_,
must be a south pole; this broken part of which we are now speaking may
be called _A B_. The other, which contains _D_, should then be placed so
as to float on water, when you will see _D_ point towards the south
because it is a south pole; but the other end at the point of fracture,
lettered _C_, will be a north pole; this stone may now be named _C D_.
If we consider the first stone as the active agent, then the second, or
_C D_, will be the passive subject. You will also notice that the ends
of the two stones which before their separation were together, after
breaking will become one a north pole and the other a south pole. If now
these same broken portions are brought near each other, one will attract
the other, so that they will again be joined at the points _B_ and _C_,
where the fracture occurred. Thus, by natural instinct, one single stone
will be formed as before. This may be demonstrated fully by cementing
the parts together, when the same effects will be produced as before the
stone was broken. As you will perceive from this experiment, the active
agent desires to become one with the passive subject because of the
similarity that exists between them. Hence _C_, being a north pole, must
be brought close to _B_, so that the agent and its subject may form one
and the same straight line in the order _A B_, _C D_ and _B_ and _C_
being at the same point. In this union the identity of the extreme parts
is retained and preserved just as they were at first; for _A_ is the
north pole in the entire line as it was in the divided one; so also _D_
is the south pole as it was in the divided passive subject, but _B_ and
_C_ have been made effectually into one. In the same way it happens that
if _A_ be joined to _D_ so as to make the two lines one, in virtue of
this union due to attraction in the order _C D A B_, then _A_ and _D_
will constitute but one point, the identity of the extreme parts will
remain unchanged just as they were before being brought together, for
_C_ is a north pole and _B_ a south, as during their separation. If you
proceed in a different fashion, this identity or similarity of parts
will not be preserved; for you will perceive that if _C_, a north pole,
be joined to _A_, a north pole, contrary to the demonstrated truth, and
from these two lines a single one, _B A C D_, is formed, as _D_ was a
south pole before the parts were united, it is then necessary that the
other extremity should be a north pole, and as _B_ is a south pole, the
identity of the parts of the former similarity is destroyed. If you make
_B_ the south pole as it was before they united, then _D_ must become
north, though it was south in the original stone; in this way neither
the identity nor similarity of parts is preserved. It is becoming that
when the two are united into one, they should bear the same likeness as
the agent, otherwise nature would be called upon to do what is
impossible. The same incongruity would occur if you were to join _B_
with _D_ so as to make the line _A B D C_, as is plain to any person who
reflects a moment. Nature, therefore, aims at being and also at acting
in the best manner possible; it selects the former motion and order
rather than the second because the identity is better preserved. From
all this it is evident why the north pole attracts the south and
conversely, and also why the south pole does not attract the south pole
and the north pole does not attract the north.


                               CHAPTER X
    AN INQUIRY INTO THE CAUSE OF THE NATURAL VIRTUE OF THE LODESTONE

Certain persons who were but poor investigators of nature held the
opinion that the force with which a lodestone draws iron, is found in
the mineral veins themselves from which the stone is obtained; whence
they claim that the iron turns towards the poles of the earth, only
because of the numerous iron mines found there. But such persons are
ignorant of the fact that in many different parts of the globe the
lodestone is found; from which it would follow that the iron needle
should turn in different directions according to the locality; but this
is contrary to experience. Secondly, these individuals do not seem to
know that the places under the poles are uninhabitable because there
one-half the year is day and the other half night. Hence it is most
silly to imagine that the lodestone should come to us from such places.
Since the lodestone points to the south as well as to the north, it is
evident from the foregoing chapters that we must conclude that not only
from the north pole but also from the south pole rather than from the
veins of the mines virtue flows into the poles of the lodestone. This
follows from the consideration that wherever a man may be, he finds the
stone pointing to the heavens in accordance with the position of the
meridian; but all meridians meet in the poles of the world; hence it is
manifest that from the poles of the world, the poles of the lodestone
receive their virtue. Another necessary consequence of this is that the
needle does not point to the pole star, since the meridians do not
intersect in that star but in the poles of the world. In every region,
the pole star is always found outside the meridian except twice in each
complete revolution of the heavens. From all these considerations, it is
clear that the poles of the lodestone derive their virtue from the poles
of the heavens. As regards the other parts of the stone, the right
conclusion is, that they obtain their virtue from the other parts of the
heavens, so that we may infer that not only the poles of the stone
receive their virtue and influence from the poles of the world, but
likewise also the other parts, or the entire stone from the entire
heavens. You may test this in the following manner: A round lodestone on
which the poles are marked is placed on two sharp styles as pivots
having one pivot under each pole so that the lodestone may easily
revolve on these pivots. Having done this, make sure that it is equally
balanced and that it turns smoothly on the pivots. Repeat this several
times at different hours of the day and always with the utmost care.
Then place the stone with its axis in the meridian, the poles resting on
the pivots. Let it be moved after the manner of bracelets so that the
elevation and depression of the poles may equal the elevation and
depressions of the poles of the heavens of the place in which you are
experimenting. If now the stone be moved according to the motion of the
heavens, you will be delighted in having discovered such a wonderful
secret; but if not, ascribe the failure to your own lack of skill rather
than to a defect in nature. Moreover, in this position I consider the
strength of the lodestone to be best preserved. When it is placed
differently, i. e., not in the meridian, I think its virtue is weakened
or obscured rather than maintained. With such an instrument you will
need no timepiece, for by it you can know the ascendant at any hour you
please, as well as all other dispositions of the heavens which are
sought for by astrologers.




                                PART II


                                PART II
                               CHAPTER I
 THE CONSTRUCTION OF AN INSTRUMENT FOR MEASURING THE AZIMUTH OF THE SUN
                  THE MOON OR ANY STAR ON THE HORIZON

Having fully examined all the properties of the lodestone and the
phenomena connected therewith, let us now come to those instruments
which depend for their operation on the knowledge of those facts. Take a
rounded lodestone,[4] and after determining its poles in the manner
already mentioned, file its two sides so that it becomes elongated at
its poles and occupies less space. The lodestone prepared in this wise
is then enclosed within two capsules after the fashion of a mirror. Let
these capsules be so joined together that they cannot be separated and
that water cannot enter; they should be made of light wood and fastened
with cement suited to the purpose. Having done this, place them in a
large vessel of water on the edges of which the two parts of the world,
i. e., the north and south points, have been found and marked. These
points may be united by a thread stretched across from north to south.
Then float the capsules and place a smooth strip of wood over them in
the manner of a diameter. Move the strip until it is equally distant
from the meridian-line, previously determined and marked by a thread, or
else until it coincides therewith. Then mark a line on the capsules
according to the position of the strip, and this will indicate forever
the meridian of that place. Let this line be divided at its middle by
another cutting it at right angles, which will give the east and west
line; thus the four cardinal points will be determined and indicated on
the edge of the capsules. Each quarter is to be subdivided into 90
parts, making 360 in the circumference of the capsules. Engrave these
divisions on them as usually done on the back of an astrolabe. On the
top or edge of the capsules thus marked place a thin ruler like the
pointer on the back of the astrolabe; instead of the sights attach two
perpendicular pins, one at each end. If, therefore, you desire to take
the azimuth of the sun, place the capsules in water and let them move
freely until they come to rest in their natural position. Hold them
firmly in one hand, while with the other you move the ruler until the
shadow of the pins falls along the length of the ruler; then the end of
the ruler which is towards the sun will indicate the azimuth of the sun.
Should it be windy, let the capsules be covered with a suitable vessel
until they have taken their position north and south. The same method,
namely, by sighting, may be followed at night for determining the
azimuth of the moon and stars; move the ruler until the ends of the pins
are in the same line with the moon or star; the end of the ruler will
then indicate the azimuth just as in the case of the sun. By means of
the azimuth may then be determined the hour of the day, the ascendant,
and all those other things usually determined by the astrolabe. A form
of the instrument is shown in the following figure.

    [Illustration: FIG. 1.—AZIMUTH COMPASS]


                               CHAPTER II
      THE CONSTRUCTION OF A BETTER INSTRUMENT FOR THE SAME PURPOSE

In this chapter I will describe the construction of a better and more
efficient instrument. Select a vessel of wood, brass or any solid
material you like, circular in shape, moderate in size, shallow but of
sufficient width, with a cover of some transparent substance, such as
glass or crystal; it would be even better to have both the vessel and
the cover transparent. At the centre of this vessel fasten a thin axis
of brass or silver, having its extremities in the cover above and the
vessel below. At the middle of this axis let there be two apertures at
right angles to each other; through one of them pass an iron stylus or
needle, through the other a silver or brass needle crossing the iron one
at right angles. Divide the cover first into four parts and subdivide
these into 90 parts, as was mentioned in describing the former
instrument. Mark the parts north, south, east and west. Add thereto a
ruler of transparent material with pins at each end. After this bring
either the north or the south pole of a lodestone near the cover so that
the needle may be attracted and receive its virtue from the lodestone.
Then turn the vessel until the needle stands in the north and south line
already marked on the instrument; after which turn the ruler towards the
sun if day-time, and towards the moon and stars at night, as described
in the preceding chapter. By means of this instrument you can direct
your course towards cities and islands and any other place wherever you
may wish to go by land or sea, provided the latitude and longitude of
the places are known to you. How iron remains suspended in air by virtue
of the lodestone, I will explain in my book on the action of mirrors.
Such, then, is the description of the instrument illustrated below. (See
Figs. 2 and 3.)

    [Illustration: FIG. 2.—DOUBLE-PIVOTED NEEDLE]

    [Illustration: FIG. 3.—PIVOTED COMPASS]


                              CHAPTER III
             THE ART OF MAKING A WHEEL OF PERPETUAL MOTION

In this chapter I will make known to you the construction of a wheel
which in a remarkable manner moves continuously. I have seen many
persons vainly busy themselves and even becoming exhausted with much
labor in their endeavors to invent such a wheel. But these invariably
failed to notice that by means of the virtue or power of the lodestone
all difficulty can be overcome. For the construction of such a wheel,
take a silver capsule like that of a concave mirror, and worked on the
outside with fine carving and perforations, not only for the sake of
beauty, but also for the purpose of diminishing its weight. You should
manage also that the eye of the unskilled may not perceive what is
cunningly placed inside. Within let there be iron nails or teeth of
equal weight fastened to the periphery of the wheel in a slanting
direction, close to one another so that their distance apart may not be
more than the thickness of a bean or a pea; the wheel itself must be of
uniform weight throughout. Fasten the middle of the axis about which the
wheel revolves so that the said axis may always remain immovable. Add
thereto a silver bar, and at its extremity affix a lodestone placed
between two capsules and prepared in the following way: When it has been
rounded and its poles marked as said before, let it be shaped like an
egg; leaving the poles untouched, file down the intervening parts so
that thus flattened and occupying less space, it may not touch the sides
of the capsules when the wheel revolves. Thus prepared, let it be
attached to the silver rod just as a precious stone is placed in a ring;
let the north pole be then turned towards the teeth or cogs of the wheel
somewhat slantingly so that the virtue of the stone may not flow
diametrically into the iron teeth, but at a certain angle; consequently
when one of the teeth comes near the north pole and owing to the impetus
of the wheel passes it, it then approaches the south pole from which it
is rather driven away than attracted, as is evident from the law given
in a preceding chapter. Therefore such a tooth would be constantly
attracted and constantly repelled.

    [Illustration: FIG. 4.—PERPETUAL MOTION WHEEL]

In order that the wheel may do its work more speedily, place within the
box a small rounded weight made of brass or silver of such a size that
it may be caught between each pair of teeth; consequently as the
movement of the wheel is continuous in one direction, so the fall of the
weight will be continuous in the other. Being caught between the teeth
of a wheel which is continuously revolving, it seeks the centre of the
earth in virtue of its own weight, thereby aiding the motion of the
teeth and preventing them from coming to rest in a direct line with the
lodestone. Let the places between the teeth be suitably hollowed out so
that they may easily catch the body in its fall, as shown in the diagram
above. (Fig. 4.)

Farewell: finished in camp at the siege of Lucera on the eighth day of
August, Anno Domini MCCLXIX.




                                 NOTES


               EARLY REFERENCES TO THE MARINER’S COMPASS

The following are the passages referred to in the introductory notice:

Abbot Neckam (1157-1217), in his _De Naturis Rerum_, writes:

“The sailors, moreover, as they sail over the sea, when in cloudy
weather they can no longer profit by the light of the sun, or when the
world is wrapped up in the darkness of the shades of night and they are
ignorant to what point their ship’s course is directed, these mariners
touch the lodestone with a needle, which (the needle) is whirled round
in a circle until when its motion ceases, its point looks direct to the
north. (_Cuspis ipsius septentrionalem plagam respiciat._)”

In his _De Utensilibus_, we read:

“Among other stores of a ship, there must be a needle mounted on a dart
(_habeat etiam acum jaculo superpositam_) which will oscillate and turn
until the point looks to the north, and the sailors will thus know how
to direct their course when the pole star is concealed through the
troubled state of the atmosphere.”[5]

Alexander Neckam was born at St. Albans in 1157, joined the Augustinian
Order and taught in the University of Paris from 1180 to 1187, after
which he returned to England to take charge of a College of his Order at
Dunstable. He was elected Abbot of Cirencester in 1213 and died at
Kemsey, near Worcester, in 1217.


The satirical poem of Guyot de Provins, written about 1208, contains the
following passage:

  The mariners employ an art which cannot deceive,
  By the property of the lodestone,
  An ugly stone and brown,
  To which iron joints itself willingly
  They have; they attend to where it points
  After they have applied a needle to it;
  And they lay the latter on a straw
  And put it simply in the water
  Where the straw makes it float.
  Then the point turns direct
  To the star with such certainty
  That no man will ever doubt it,
  Nor will it ever go wrong.
  When the sea is dark and hazy,
  That one sees neither star nor moon,
  Then they put a light by the needle
  And have no fear of losing their way.
  The point turns towards the star;
  And the mariners are taught
  To follow the right way.
  It is an art which cannot fail.

Provins, from which Guyot took his surname, was a small town in the
vicinity of Paris.


Cardinal Jacques de Vitry, in his _Historia Orientalis_, Cap. 89,
writes:

“An iron needle, after having been in contact with the lodestone, turns
towards the north star, so that it is very necessary for those who
navigate the seas.”

Jacques de Vitry was born at Argenteuil, near Paris, joined the fourth
crusade, became Bishop of Ptolemais, and died in Rome in 1244. He wrote
his “Description of Palestine,” which forms the first book of his
_Historia Orientalis_, in the East, between 1215 and 1220.


Albertus Magnus (1193-1280) in his _De Mineralibus_, Lib. II., Tract 3,
Cap. 6, writes:

“It is the end of the lodestone which makes the iron that touched it
turn to the north (_ad zoron_) and which is of use to mariners; but the
other end of the needle turns toward the south (_ad aphron_).”

This illustrious Bavarian schoolman joined the Dominican Order in his
youth, lectured to great audiences in Cologne, became bishop of
Ratisbonne in 1260, and died in 1280. Thomas Aquinas the greatest of
schoolmen, was among his pupils.


In the Spanish code of laws, begun in 1256, during the reign of Alfonso
el Sabio, and known as _Las Siete Partidas_, we read:

“Just as mariners are guided during the night by the needle, which
replaces for them the shores and pole star alike, by showing them the
course to pursue both in fair weather and foul, so those who are called
upon to advise the King must always be guided by a spirit of justice.”


Brunetto Latini, in his _Trésor des Sciences_, 1260, writes:

“The sailors navigate the seas guided by the two stars called the
tramontanes, and each of the two parts of the lodestone directs the end
of the needle to the star to which that part itself turns.”

Brunetto Latini (1230-1294) was a man of great eminence in the
thirteenth century; Dante was among his pupils at Florence. For
political reasons, he removed to Paris, where he wrote his _Trésor_ and
also his _Tesoretto_. He visited Roger Bacon at Oxford about 1260.


In his treatise _De Contemplatione_, begun in 1272, Raymond Lully
writes:

“As the needle, after having touched the lodestone, turns to the north,
so the mariner’s needle (_acus nautica_) directs them over the sea.”

Lully was born at Palma in the Island of Majorca in 1236; he joined the
Third Order of St. Francis, dying in 1315.


Ristoro d’Arezzo, in his _Libro della Composizione del Mundo_, written
in 1282, has the following:

“Besides this, there is the needle which guides the mariner, and which
is itself directed by the star called the tramontane.”[6]


The following metrical translation of a poem by Guido Guinicelli, an
Italian priest, 1276, is from the pen of Dr. Park Benjamin, of New York:

  In what strange regions ’neath the polar star
  May the great hills of massy lodestone rise,
  Virtue imparting to the ambient air
  To draw the stubborn iron; while afar
  From that same stone, the hidden virtue flies
  To turn the quivering needle to the Bear
  In splendor blazing in the Northern skies.

The above extracts show that the directive property of the magnetic
needle was well known in England, France, Germany, Spain and Italy in
the thirteenth century. In the passage from Neckam, the _acum jaculo
superpositam_ has been construed by some to mean a form of pivoted
needle, while in the letter of Peregrinus, 1269, the double pivoted form
is clearly described.




                               Footnotes


[1]With very few exceptions all the works referred to in this notice
    will be found in the Wheeler Collection in the Library of the
    American Institute of Electrical Engineers, New York.

[2]It is probable that Flavio Gioja, an Italian pilot, some fifty years
    later, added the compass-card and attached it to the magnet.

[3]Annali di Matematica Pura ed Applicata, 1865.

[4]A terrella, or earthkin.

[5]The Chronicles and Memoirs of Great Britain and Ireland during the
    Middle Ages, by Thomas Wright (1863).

[6]The pole-star was thus named in the south of France and the north of
    Italy because seen beyond the mountains (the Alps).




                          Transcriber’s Notes


—Retained publication and copyright information from the original; this
  eBook is public-domain in the U.S.

—Silently corrected a few palpable typographical errors.

—In the text versions, enclosed italicized text in _underscore_.







End of the Project Gutenberg EBook of The Letter of Petrus Peregrinus on the
Magnet, A.D. 1269, by Petrus Peregrinus

*** 