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  [Illustration: Fig. 1. THE SOLAR SYSTEM.
  _Frontispiece._]




  COMETS AND METEORS:

  THEIR PHENOMENA IN ALL AGES;
  THEIR MUTUAL RELATIONS;
  AND THE
  THEORY OF THEIR ORIGIN.


  BY
  DANIEL KIRKWOOD, LL.D.,

  PROFESSOR OF MATHEMATICS IN INDIANA UNIVERSITY,
  AND AUTHOR OF "METEORIC ASTRONOMY."


  [Illustration]


  PHILADELPHIA:
  J. B. LIPPINCOTT & CO.
  1873.




  Entered according to Act of Congress, in the year 1873, by
  DANIEL KIRKWOOD, LL.D.,
  In the Office of the Librarian of Congress at Washington.




PREFACE.


The origin of meteoric astronomy, as a science, dates from the memorable
star-shower of 1833. Soon after that brilliant display it was found that
similar phenomena had been witnessed, at nearly regular intervals, in
former times. This discovery led at once to another no less important,
viz.: that the nebulous masses from which such showers are derived
revolve about the sun in paths intersecting the earth's orbit. The
theory that these meteor-clouds are but the scattered fragments of
disintegrated comets was announced by several astronomers in 1867:--a
theory confirmed in a remarkable manner by the shower of meteors from
the _debris_ of Biela's comet on the 27th of November, 1872.

To gratify the interest awakened in the public mind by the discoveries
here named, is the main design of the following work. Among the subjects
considered are, cometary astronomy; aerolites, with the phenomena
attending their fall; the most brilliant star-showers of all ages; and
the origin of comets, aerolites, and falling stars.

It may be proper to remark that the language used by the writer in a
volume[1] published several years since, and now nearly out of print,
has been occasionally adopted in the following treatise.

BLOOMINGTON, INDIANA, April, 1873.

  [1] Meteoric Astronomy.




CONTENTS.


                                                       PAGE.
  PREFACE                                                  3

  CHAPTER I.
    A GENERAL VIEW OF THE SOLAR SYSTEM                     9

  CHAPTER II.
    COMETS                                                13
    COMETS VISIBLE IN THE DAY-TIME                        15
    PERIODIC COMETS                                       18

  CHAPTER III.
    COMETS WHOSE ELEMENTS INDICATE PERIODICITY, BUT
      WHOSE RETURNS HAVE NOT BEEN RECOGNIZED              31

  CHAPTER IV.
    OTHER REMARKABLE COMETS                               39

  CHAPTER V.
    THE POSITION AND ARRANGEMENT OF COMETARY ORBITS       43

  CHAPTER VI.
    THE DISINTEGRATION OF COMETS                          49

  CHAPTER VII.
    METEORIC STONES                                       57

  CHAPTER VIII.
    SHOOTING-STARS--METEORS OF NOVEMBER 14                69

  CHAPTER IX.
    OTHER METEORIC STREAMS                                82

  CHAPTER X.
    THE ORIGIN OF COMETS AND METEORS                      94




I.

COMETS.




COMETS AND METEORS.




CHAPTER I.

A GENERAL VIEW OF THE SOLAR SYSTEM.


A descriptive treatise on COMETS and METEORS may properly be preceded by
a brief general view of the _planetary_ system to which these bodies are
related, and by which their motions, in direction and extent, are
largely influenced.

THE SOLAR SYSTEM consists of the sun, together with the planets, comets,
and meteors which revolve around it as the centre of their motions. The
sun is the great controlling orb of this system, and the source of light
and heat to its various members. Its magnitude is one million three
hundred thousand times greater than that of the earth, and it contains
more than seven hundred times as much matter as all the planets put
together.

Mercury is the nearest planet to the sun; its mean distance being about
35,400,000 miles. Its diameter is 3000 miles, and it completes its
orbital revolution in 88 days.

Venus, the next member of the system, is sometimes our morning and
sometimes our evening star. Its magnitude is almost exactly the same as
that of the earth. It revolves round the sun in 225 days.

The earth is the third planet from the sun in the order of distance; the
radius of its orbit being about 92,000,000 miles. It is attended by one
satellite,--the moon,--the diameter of which is 2160 miles.

Mars is the first planet exterior to the earth's orbit. It is
considerably smaller than the earth, and has no satellite. It revolves
round the sun in 687 days.

_The Asteroids._--Since the commencement of the present century a
remarkable zone of telescopic planets has been discovered immediately
exterior to the orbit of Mars. These bodies are extremely small; some of
them probably containing less matter than the largest mountains on the
earth's surface. 131 members of the group are known at present, and the
number is annually increasing.

Jupiter, the first planet exterior to the asteroids, is nearly
500,000,000 miles from the sun, and revolves round it in a little less
than 12 years. This planet is 86,000 miles in diameter, and contains
more than twice as much matter as all the other planets, primary and
secondary, put together. Jupiter is attended by four moons or
satellites.

Saturn is the sixth of the principal planets in the order of distance.
Its orbit is about 400,000,000 miles beyond that of Jupiter. This planet
is attended by eight satellites, and is surrounded by three broad flat
rings. Saturn is 73,000 miles in diameter, and its mass or quantity of
matter is more than that of all the other planets except Jupiter.

Uranus is at double the distance of Saturn, or nineteen times that of
the earth. Its diameter is about 34,000 miles, and its period of
revolution 84 years. It is attended by at least four satellites.

Neptune is the most remote known member of the system; its distance
being 2,800,000,000 miles. It is somewhat larger than Uranus; has
certainly one satellite, and probably several more. Its period is about
165 years. A cannon-ball flying outward from the sun at the uniform
velocity of 500 miles per hour would not reach the orbit of Neptune in
less than 639 years.

These planets all move round the sun in the same direction,--from west
to east. Their motions are nearly circular, and also nearly in the same
plane. Their orbits, except that of Neptune, are represented in the
frontispiece. It is proper to remark, however, that all representations
of the solar system by maps and planetariums must give an exceedingly
erroneous view either of the magnitudes or distances of its various
members. If the earth, for instance, be denoted by a ball half an inch
in diameter, the diameter of the sun, according to the same scale
(16,000 miles to the inch), will be between four and five feet; that of
the earth's orbit, about 1000 feet; while that of Neptune's orbit will
be nearly six miles. To give an accurate representation of the solar
system at a single view is therefore plainly impracticable.

THE ZODIACAL LIGHT.--This term was first applied by Dominic Cassini, in
1683, to a faint nebulous aurora, somewhat resembling the milky way,
apparently of a conical or lenticular form, having its base toward the
sun and its axis nearly in the direction of the ecliptic. The most
favorable time for observing it is when its axis is most nearly
perpendicular to the horizon. This, in our latitudes, occurs in March,
for the evening, and in October, for the morning. The angular distance
of its vertex from the sun is frequently seventy or eighty degrees,
while sometimes, though rarely (except within the tropics), it exceeds
even one hundred degrees. It was noticed in the latter part of the 16th
century by Tycho Brahe. The first accurate description of the phenomenon
was given, however, by Cassini. This astronomer supposed the appearance
to be produced by the blended light of innumerable bodies too small to
be separately observed,--a theory still very generally accepted. In
other words, the zodiacal light is probably a swarm of infinitesimal
planets; the greater part of the cluster being interior to Mercury's
orbit.

The distances between the different members of our planetary system,
vast as they may seem, sink into insignificance when compared with the
intervals which separate us from the so-called fixed stars. _Alpha
Centauri_, the nearest of those twinkling luminaries, is 7000 times more
distant than Neptune from the sun. Even light itself, which moves
185,000 miles in a second, is more than three years in traversing the
mighty interval.




CHAPTER II.

COMETS.


The term _comet_--which signifies literally a _hairy star_--may be
applied to all bodies that revolve about the sun in very eccentric
orbits. The sudden appearance, vast dimensions, and extraordinary aspect
of these celestial wanderers, together with their rapid and continually
varying motions, have never failed to excite the attention and wonder of
all observers. Nor is it surprising that in former times, when the
nature of their orbits was wholly unknown, they should have been looked
upon as omens of impending evil, or messengers of an angry Deity. Even
now, although modern science has reduced their motions to the domain of
law, determined approximately their orbits, and assigned in a number of
instances their periods, the interest awakened by their appearance is in
some respects still unabated.

The special points of dissimilarity between planets and comets are the
following:--The former are dense, and, so far as we know, solid bodies;
the latter are many thousand times rarer than the earth's atmosphere.
The planets _all_ move from west to east; many comets revolve in the
opposite direction. The planetary orbits are but slightly inclined to
the plane of the ecliptic; those of comets may have any inclination
whatever. The planets are observed in all parts of their orbits;
comets, only in those parts nearest the sun.

The larger comets are attended by a _tail_, or train of varying
dimensions, extending generally in a direction opposite to that of the
sun. The more condensed part, from which the tail proceeds, is called
the _nucleus_; and the nebulous envelope immediately surrounding the
nucleus is sometimes termed the _coma_. These different parts are seen
in Fig. 2, which represents the great comet of 1811.

[Illustration: Fig. 2. THE GREAT COMET OF 1811.]

Zeno, Democritus, and other Greek philosophers held that comets were
produced by the collection of several stars into clusters. Aristotle
taught that they were formed by exhalations, which, rising from the
earth's surface, ignited in the upper regions of the atmosphere. This
hypothesis, through the great influence of its author, was generally
received for almost two thousand years. Juster views, however, were
entertained by the celebrated Seneca, who maintained that comets ought
to be ranked among the permanent works of nature, and that their
disappearance was not an extinction, but simply a passing beyond the
reach of our vision. The observations of Tycho Brahe first established
the fact that comets move through the planetary spaces far beyond the
limits of our atmosphere. The illustrious Dane, however, supposed them
to move in circular orbits. Kepler, on the other hand, was no less in
error in considering their paths to be rectilinear. James Bernoulli
supposed comets to be the satellites of a very remote planet, invisible
on account of its great distance,--such satellites being seen only in
the parts of their orbits nearest the earth. Still more extravagant
was the hypothesis of Descartes, who held that they were originally
fixed stars, which, having gradually lost their light, could no longer
retain their positions, but were involved in the vortices of the
neighboring stars, when such as were thus brought within the sphere of
the sun's illuminating power again became visible.


_Comets visible in the daytime._

Comets of extraordinary brilliancy have sometimes been seen during the
daytime. At least thirteen authentic instances of this phenomenon have
been recorded in history. The first was the comet which appeared about
the year 43 B.C., just after the assassination of Julius Caesar. The
Romans called it the _Julium Sidus_, and regarded it as a celestial
chariot sent to convey the soul of Caesar to the skies. It was seen two
or three hours before sunset, and continued visible for eight successive
days. The great comet of 1106, described as an object of terrific
splendor, was seen simultaneously with the sun, and in close proximity
to it. Dr. Halley supposed this and the Julian comet to have been
previous visits of the great comet of 1680. In the year 1402 two comets
appeared,--one about the middle of February, the other in June,--both of
which were visible while the sun was above the horizon. One was of such
magnitude and brilliancy that the nucleus and even the tail could be
seen at midday. The comet of 1472, one of the most splendid recorded in
history, was visible in full daylight, when nearest the earth, on the
21st of January. This comet, according to Laugier, moves very nearly in
the plane of the ecliptic, its inclination being less than two degrees.
Its least distance from our globe was only 3,300,000 miles. The comet of
1532, supposed by some to be identical with that of 1661, was also
visible in full sunshine. The apparent magnitude of its nucleus was
three times greater than that of Jupiter. The comet of 1577 was seen
with the naked eye by Tycho Brahe before sunset. It was by observations
on this body that Aristotle's doctrine in regard to the origin, nature,
and distance of comets was proved to be erroneous. It was simultaneously
observed by Tycho at Oranienberg, and Thaddeus Hagecius at Prague; the
points of observation being more than 400 miles apart, and nearly on the
same meridian. The comet was found to have no sensible diurnal parallax;
in other words, its apparent place in the heavens was the same to each
observer, which could not have been the case had the comet been less
distant than the moon. The comet which passed its perihelion on the 8th
of November, 1618, was distinctly seen by Marsilius when the sun was
above the horizon. The great comet of 1744 was seen without the aid of a
glass at one o'clock in the afternoon,--only five hours after its
perihelion passage. The diameter of this body was nearly equal to that
of Jupiter. It had _six_ tails, the greatest length of which was about
30,000,000 miles, or nearly one-third of the distance of the earth from
the sun. The spaces between the tails were as dark as the rest of the
heavens, while the tails themselves were bordered with a luminous edging
of great beauty.

The great comet of 1843 was distinctly visible to the naked eye, at
noon, on the 28th of February. It appeared as a brilliant body, within
less than two degrees from the sun. This comet passed its perihelion on
the 27th of February, at which time its distance from the sun's surface
was only about one-fourth of the moon's distance from the earth. This is
the nearest approach to the sun ever made by any known comet. The
velocity of the body in perihelion was about 1,280,000 miles an hour, or
nearly nineteen times that of the earth in its orbit. The apparent
length of its tail was sixty-five degrees, and its true length
150,000,000 miles. The first comet of 1847, discovered by Mr. Hind, was
also seen near the sun on the day of its perihelion passage. That
discovered by Klinkerfues on the 10th of June, 1853, and which passed
its perihelion on the 1st of September, was seen at Olmutz in the
daytime, August 31, when only twelve degrees from the sun. After passing
its perihelion, it was again observed, _at noon_, on the 2d, 3d, and 4th
of September. Finally, the great comet of 1861 was seen before sunset,
on Monday evening, July 1, by Rev. Henry W. Ballantine, of Bloomington,
Indiana. It was again detected on the following evening just as the sun
was in the horizon.

Besides the thirteen comets which we have enumerated, at least four
others have been seen in the daytime; all, however, under peculiar
circumstances. Seneca relates that during a great solar eclipse, 63
years before our era, a large comet was observed not far from the sun.
"Philostorgius says that on the 19th of July, A.D. 418, when the sun
was eclipsed and stars were visible, a great comet, in the form of a
cone, was discovered near that luminary, and was afterwards observed
during the nights."[2] The comet which passed its perihelion on the 18th
of November, 1826, was observed by both Gambart and Flaugergues to
transit the solar disk,--the least distance of the nucleus from the
sun's surface being about 2,000,000 miles. The second comet of 1819 and
the comet of 1823 are both known in like manner to have passed between
the sun and the earth. Unfortunately, however, the transits were not
observed.

  [2] Hind.

A few cometary orbits are hyperbolas, more ellipses, and a still greater
number parabolas. Comets moving in ellipses remain permanently within
the limits of solar influence. Others, however, visit our system but
once, and then pass off to wander indefinitely in the sidereal spaces.


_Comets of known periodicity._

I. Halley's Comet.

As comets are subject to great changes of appearance, one can never be
identified by any description of its magnitude, brilliancy, etc., at the
time of a previous return. This can be done only by a comparison of
orbits. If, for example, we find the elements of an orbit very nearly
corresponding in every particular with those of a former comet, there is
a degree of probability, amounting almost to certainty, that the two
are identical. Sir Isaac Newton, in his _Principia_, published shortly
after the appearance of the comet of 1682, explained how the periods of
those mysterious visitors might thus be ascertained, thus directing the
attention of astronomers to the subject. Dr. Halley soon after undertook
a thorough discussion of all the recorded cometary observations within
his reach. In the course of his investigations he discovered that the
path of the comet observed by Kepler in 1607 coincided almost exactly
with that of the one which passed its perihelion in 1682. Hence he
concluded that they were the same. He found also that the comet of 1531,
whose course had been particularly observed by Apian, moved in the same
path. The interval between the consecutive appearances being nearly 76
years, Halley announced this as the time of the comet's revolution, and
boldly predicted its return in 1758 or 1759. The law of universal
gravitation had at this time just been discovered and announced. But
although its application to the determination of planetary and cometary
perturbations had not been developed, Halley was well aware that the
attractive influence of Jupiter and Saturn might accelerate or <DW44>
the motion of the comet, so as to produce a considerable variation in
its period. During the interval from 1682 to 1759, the application of
the higher mathematics to problems in physical astronomy had been
studied with eminent success. The disturbing effect of the two large
planets, Jupiter and Saturn, was computed with almost incredible labor
by Clairaut, Lalande, and Madame Lepaute. The result as announced by
Clairaut to the Academy of Sciences in November, 1758, was that the
period must be 618 days longer than that immediately preceding, and that
the comet accordingly would pass its perihelion about the 13th of April,
1759. It was stated, however, that, being pressed for want of time, they
had neglected certain quantities which might somewhat affect the result.
The comet, in fact, passed its perihelion in March, within less than a
month of the predicted time. When it is considered that the attraction
of the earth was not taken into the account, and that Uranus, whose
influence must have been sensible, had not then been discovered, this
must certainly be regarded as a remarkable approximation.

But during the next interval of 76 years the theory of planetary
perturbations had been more perfectly developed. The masses of Jupiter
and Saturn had been determined with greater accuracy, and Uranus had
been added to the known members of the planetary system. A nearer
approximation to the exact time of the comet's perihelion passage in
1835 was therefore to be expected. Prizes were offered by two of the
learned societies of Europe--the Academy of Sciences at Turin, and the
French Institute--for the most perfect discussion of its motions. That
of the former was awarded to Damoiseau,--that of the latter to
Pontecoulant. The times assigned by these distinguished mathematicians
for the comet's perihelion passage were very nearly the same, and
differed but a few days from the true time. Had the present received
mass of Jupiter been used in the calculations, Pontecoulant, it is
believed, would not have been in error as much as 24 hours. It may be
proper to remark that, during the entire period from 1759 to 1835, the
position of Neptune was such that it could produce no considerable
effect on the motion of the comet.

This interesting object will again return about 1911.

The visit of 1531 was the earliest that Halley succeeded in determining
with any degree of certainty. Peter Apian, by whom it was at that time
observed, was the first European to ascertain the fact that, as a
general thing, the tails of comets are turned from the sun.[3] To
confirm this discovery, he carefully followed the body in its progress
through the constellations. By means of his recorded observations Halley
was enabled to identify this comet with that of 1607 and 1682. The great
comet of 1456 he _conjectured_ to be the same, from the date of its
appearance. Pingre subsequently confirmed this suspicion by a careful
examination of the few trustworthy records that could be collected from
the writers of that period.

  [3] The Chinese, however, as appears from Biot's researches, had
      observed the same fact 700 years earlier. See Humboldt's Cosmos,
      vol. iv. (Bohn's ed.), p. 544.

From the earlier descriptions of this comet we infer that its brilliancy
is gradually diminishing. In 1456 its tail, which was slightly curved
like a sword or sabre, extended two-thirds of the distance from the
horizon to the zenith. The appearance of such an object, in a grossly
superstitious age, excited throughout Europe the utmost consternation.
The Moslems had just taken Constantinople, and were threatening to
advance westward into Europe. Pope Calixtus III., regarding the comet as
confederate with the Turk, ordered prayers to be offered three times a
day for deliverance from both. The alarm, however, was of short
duration. Within ten days of its appearance the comet reached its
perihelion. Receding from the sun, the sword-like form began to diminish
in brilliancy and extent; and finally, to the great relief of Europe, it
entirely disappeared.

The perihelion passage of 1456 was, until recently, the earliest known.
It was shown by Laugier, however, in 1843, that among the notices of
comets extracted by Edward Biot from the Chinese records, were
observations of a body in 1378, which was undoubtedly the comet of
Halley. Further researches among these annals enabled the same
astronomer to recognize two ancient returns, one in 760, the other in
451. Still more recently the distinguished English astronomer, Mr. Hind,
has traced back the returns to the year 11 B.C. He remarks, however,
that previous to that epoch, "the Chinese descriptions of comets are too
vague to aid us in tracing any more ancient appearances," and that
"European writers of these remote times render us no assistance." Let us
now inquire whether the comet had probably made any former approach to
the sun in an orbit nearly identical with the present. It is well known
that the modern period of this body is considerably less than the
ancient. Thus, the mean period since A.D. 1456 has been 75.88 years;
while from 11 B.C. to 1456 A.D. it was 77.27 years. In determining the
approximate dates of former returns, the ancient period should evidently
be employed. Now, it is a remarkable fact that of more than 70
comets,[4] or objects supposed to be comets, whose appearance was
recorded during the six centuries immediately preceding the year 11
B.C., but one--that of 166 B.C.--was observed at a date corresponding
nearly to that of a former return of Halley's comet. Of this object it
is merely recorded that "a torch was seen in the heavens." Whether this
was a comet or some other phenomenon, it is impossible to determine. But
as the comet of Halley was more brilliant in ancient than in modern
times, it seems highly improbable that seven _consecutive_ returns of so
conspicuous an object should have been unrecorded, especially as twelve
comets per century[5] were observed during the same period. It would
appear, therefore, that the perihelion passage of 11 B.C. was in fact
the first ever made by the comet, or at least the first in an orbit
nearly the same as the present.

  [4] See the Catalogues of Chambers and Williams.

  [5] The average number.

The motion of Halley's comet is retrograde. The point of its nearest
approach to the sun is situated within the orbit of Venus. Its greatest
distance from the centre of the system is nearly twice that of Uranus,
or 36 times that of the earth. The comet is, consequently, subject to
great changes of temperature. When nearest the sun its light and heat
are almost four times greater than the earth's; when most remote, they
are 1200 times less. In the former position, the sun would appear much
larger than to us; in the latter, his apparent diameter would not
greatly exceed that of Jupiter, as viewed from the earth. It would be
difficult to conjecture what the consequences might be, were our planet
transported to either of these extremes of the cometary path. In the
perihelion, the waters of the ocean would undoubtedly be reduced to a
state of vapor; in the aphelion, they would be solidified by
congelation.


II. Encke's Comet.

It was formerly supposed that all comets have their aphelia far beyond
the limits of the planetary system. In 1818, however, a small comet was
discovered by Pons, the orbit of which was subsequently found to be
wholly interior to that of Jupiter. Its elements were presented by
Bouvard, in 1819, to the Board of Longitude at Paris. The form and
position of the orbit were immediately found to correspond with those of
a comet observed by several astronomers in 1805. The different
appearances were consequently regarded as returns of the same body. Its
elliptic orbit was calculated by Encke, who found its period to be only
about three years and four months. Its perihelion is within the orbit of
Mercury; its aphelion, between the asteroids and the orbit of Jupiter.

Encke's comet is invisible to the naked eye, except in very favorable
circumstances; it has no tail; its motion, like that of the planets, is
from west to east; and its orbit is inclined about 13 deg. to the ecliptic.

A comparison of the successive periods of this interesting object has
led to the discovery that its time of revolution is gradually
diminishing; a fact regarded by Encke and other astronomers as
indicating the existence of an ethereal medium.


III. Biela's Comet.

The discovery of Encke's comet of short period was followed, in 1826, by
that of another, whose revolution is completed in about six years and
eight months. It was observed on the 27th of February, by M. Biela, an
Austrian officer; accordingly it has since been known as _Biela's
comet_. On computing its elements and comparing them with those of
former comets, it was found to have been observed in 1772 and 1805.
Damoiseau having calculated the dimensions of the comet's elliptic path
and the time of its return, announced as the result of his computations
the remarkable fact that the orbits of the earth and comet intersect
each other, and that the comet would cross the earth's path on the 29th
of October, 1832. This produced no little alarm among the uneducated,
especially in France. Even some journalists are said to have predicted
the destruction of our globe by a collision with the comet. When the
latter, however, passed the point of intersection at the predicted time,
the earth was at a distance of 50,000,000 miles.

At the return of 1845-6, Biela's comet exhibited a most remarkable
appearance. Instead of a single comet, it appeared as two distinct
bodies moving together side by side, at a distance from each other
somewhat less than that of the moon from the earth. Astronomers,
anxious to determine whether the cometary fragments had continued
separate during an entire revolution, awaited the next return with no
ordinary interest. The _two_ bodies appeared at the predicted time
(September, 1852); their distance apart having increased to 1,250,000
miles. In 1859 the comet, on account of its proximity to the sun,
entirely escaped detection. At the return in 1865-6 the position of the
object was quite favorable for observation, yet the search of
astronomers was again unsuccessful. In 1872 the body escaped detection
both in Europe and America. One fragment was seen, however, at Madras,
India, on the mornings of the 2d and 3d of December,--several weeks
after its perihelion passage. The comet's non-appearance in 1866 and its
greatly diminished magnitude in 1872 leave no room to doubt its
progressive dissolution. This subject will again be referred to in
discussing the phenomena of meteoric showers.


IV. Faye's Comet.

On the 22d of November, 1843, M. Faye, of the Paris Observatory,
discovered a comet, which was shown by Dr. Goldschmidt to revolve in an
elliptic orbit, the perihelion of which is exterior to the orbit of
Mars, and the aphelion immediately beyond that of Jupiter. The
eccentricity is, therefore, less than that of any other comet previously
discovered. Its period is about 7 years and 5 months.

It is possible that a comet moving in a parabola or hyperbola, with the
sun in the focus, may be thrown into an elliptic orbit by the disturbing
influence of Jupiter or one of the other large planets. The celebrated
Leverrier undertook to determine whether the comet of Faye had in this
manner been recently fixed as a permanent member of the solar system. He
found that it could not have been so introduced since 1747, and,
consequently, that it must have completed at least thirteen revolutions
before its discovery.

This comet has been observed at each return from 1843 to the present
time.


V. De Vico's Comet.

On the 22d of August, 1844, De Vico, of Rome, discovered a comet whose
orbit is included between those of the earth and Jupiter. Its period is
1996 days, or about 5-1/2 years. This body, from some cause,--perhaps a
gradual dissolution,--has not been observed at any subsequent return.


VI. Brorsen's Comet.

On the 26th of February, 1846, Mr. Brorsen, of Kiel, discovered a faint
comet, the mean distance and period of which are almost identical with
those of De Vico's. This comet was not observed during the perihelion
passage of 1851, on account of its unfavorable position with respect to
the sun. It has, however, been subsequently detected.


VII. D'Arrest's Comet.

Dr. D'Arrest discovered a comet on the 27th of June, 1851, which was
soon found to move in an elliptic orbit, with a period of about 6-1/2
years. It entirely escaped observation, both in Europe and America,
during its perihelion passage in 1857. It was observed, however, at the
Cape of Good Hope. Its invisibility in 1864 was due to its unfavorable
position. At its return in 1870, it was first seen on the 31st of
August, by Dr. Winnecke, of Carlsruhe.


VIII. Tuttle's Comet.

A faint telescopic comet was discovered at the Observatory of Harvard
College, on the evening of January 4, 1858, by Mr. H. P. Tuttle. The
same body was independently found one week later by Dr. Bruhns, of
Berlin. From observations made at Cambridge, Massachusetts, and Ann
Arbor, Michigan, its elements were soon computed by different
astronomers; the result in each case coinciding so closely with the
elements of the second comet of 1790, as to place its identity wholly
beyond doubt. Its period is nearly 13 years and 8 months. It had
returned, therefore, without detection, in the years 1803, 1817, 1831,
and 1844. On its approach to perihelion in 1871, it was first detected
by M. Borelly, of Marseilles.


IX. Winnecke's Comet.

The second comet of 1858 was discovered on the 8th of March, by Dr.
Winnecke, of Bonn. This proved to be identical with the third comet of
1819, whose period was computed by Encke to be about 5-1/2 years. It had
therefore returned unperceived no less than six times between 1819 and
1858. At its return in 1863 it again escaped detection. The perihelion
passage of 1869 was made on the 30th of June. The comet was seen as
early as April 13, and, after passing the sun, as late as October 11.
"Schoenfeld states that in part of April and May it appeared to have not
one, but several, centres of condensation, and Vogel says that, in the
beginning of June, it had a much greater resemblance to a star-cluster
than to a nebula." This phenomenon, it may be remarked, bore a striking
resemblance to the appearances observed in the comets of 389, 1618, and
1661.


X. Tempel's Comet.

On the 19th of December, 1865, M. Tempel, of Marseilles, discovered a
small comet, which continued visible four weeks, passing its perihelion
January 11, 1866. Dr. Oppolzer, of Vienna, after a careful determination
of its elements, announced the interesting fact that its orbit very
nearly intersects those of the earth and Uranus; the perihelion being
situated immediately within the former, and the aphelion a short
distance exterior to the latter. The period, according to the same
astronomer, is 33 years and 65 days. The identity of this comet with
that of 1366 was suggested by Professor H. A. Newton soon after its
appearance,--a suggestion which subsequent research has strongly
corroborated. It is also highly probable that the comet observed in
China, September 29, 1133, was a former return of the same body. In 1366
it was conspicuous to the naked eye, while in 1866 it was wholly
invisible without a telescope,--a fact indicative of its gradual
dissolution. The connection of this comet with the meteors of November
14 will be elsewhere considered.


XI. The Second Comet of 1867.

Another comet of short period was discovered by M. Tempel on the 3d of
April, 1867. Its orbit is the least eccentric of all known comets: the
perihelion being exterior to the orbit of Mars; the aphelion interior to
that of Jupiter. Its motion is direct, and it completes a revolution in
5 years and 8 months.




CHAPTER III.

COMETS WHOSE ELEMENTS INDICATE PERIODICITY, BUT WHOSE RETURNS HAVE NOT
BEEN RECOGNISED.


I. The Group whose periods are nearly equal to that of Uranus.

Since the commencement of the present century five comets have been
discovered, which form, with Halley's, an interesting and remarkable
group. The first of these was detected by Pons, on the 20th of July,
1812; the second by Olbers, on the 6th of March, 1815; the third by De
Vico, on the 28th of February, 1846; the fourth by Brorsen, on the 20th
of July, 1847; and the last by Westphal, on the 27th of June, 1852. The
periods of these bodies are all nearly equal, ranging from 68 to 76
years; their eccentricities are not greatly different; the motions of
all, except that of Halley's, are direct; and the distances of their
aphelia are somewhat greater than Neptune's distance from the sun. Of
this group, the comets of 1812 and 1846 seem worthy of special notice.
The former became visible to the naked eye shortly after its discovery,
and each continued visible about ten weeks. Their elements are as
follows:

  Perihelion Passage.   1812, Sept.      1846, Mar.
                          15_d._ 7_h._      5_d._ 12_h._
  Long. of Perih'n.       92 deg. 51'          90 deg. 31'
  Long. of A. Node.      253 deg. 33'          77 deg. 37'
  Incl.                   73 deg. 57'          85 deg.  6'
  Peri'n Dist.             0.7771           0.6637
  Eccentricity.            0.94454          0.96224
  Period.                 70.68_y_         73.715
  Direction.              D                D
  Computer.               Encke.           Peirce.

The wonderful similarity of these elements, except in the longitude of
the ascending node, is at once apparent. It will also be noticed that
the longitude of the _descending_ node of the latter is very nearly
coincident with that of the _ascending_ node of the former. These
remarkable coincidences are presented to the eye in the following
diagram, where the dotted ellipse represents the orbit of the comet of
1812, and the continuous curve that of the comet of 1846.

[Illustration: Fig. 3.]

It is infinitely improbable that these coincidences should be
accidental; they point undoubtedly to a common origin of the two bodies.

According to the theory now generally accepted, comets enter the solar
system _ab extra_, move in parabolas or hyperbolas around the sun, and,
if undisturbed by the planets, pass off beyond the limits of the sun's
attraction, to be seen no more. If in their motion, however, they
approach very near any of the larger planets, their direction is changed
by planetary perturbation,--their orbits being sometimes transformed
into ellipses. The new orbits of such bodies would pass very nearly
through the points at which their greatest perturbation occurred; and
accordingly we find that the aphelia of a large proportion of the
periodic comets are near the orbits of the major planets. "I admit,"
says M. Hoek, "that the orbits of comets are by nature parabolas or
hyperbolas, and that in the cases when elliptical orbits are met with,
these are occasioned by planetary attractions, or derive their character
from the uncertainty of our observations. To allow the contrary would be
to admit some comets as permanent members of our planetary system, to
which they ought to have belonged since its origin, and so to assert the
simultaneous birth of that system and of these comets. As for me, I
attribute to these a primitive wandering character. Traveling through
space, they move from one star to another in order to leave it again,
provided they do not meet any obstacle that may force them to remain in
its vicinity. Such an obstacle was Jupiter, in the neighborhood of our
sun, for the comets of Lexell and Brorsen, and probably for the greater
part of periodical comets; the other part of which may be indebted for
their elliptical orbits to the attractions of Saturn and the remaining
planets.

"Generally, then, comets come to us from some star or other. The
attraction of our sun modifies their orbit, as had been done already by
each star through whose sphere of attraction they had passed. We can put
the question if they come as single bodies or united in systems."

The conclusion of this astronomer's interesting discussion is that--

"_There are systems of comets in space that are broken up by the
attraction of our sun, and whose members attain, as isolated bodies, the
vicinity of the earth during a course of several years._"[6]

  [6] Monthly Notices of the R. A. S., vol. xxv., p. 243.

In the researches here referred to, it is shown by Professor Hoek that
the comets of 1860 III., 1863 I., and 1863 IV. formed a group in space
previous to their entrance into our system. The same fact has also been
demonstrated in regard to other comets which need not here be specified.
Now, the comets of 1812 and 1846 IV. have their aphelia near the orbit
of Neptune, and hence the original parabolas in which they moved were
probably transformed into ellipses by the perturbations of that planet.
Before entering the solar domain, they were doubtless members of a
cometary system. Passing Neptune near the same time, and at some
distance from each other, their different relative positions with regard
to the disturbing body may account for the slight differences in the
elements of their orbits.


_Comets of the Jovian Group._

Besides the eight comets enumerated in Chapter II. whose aphelia are in
the vicinity of Jupiter's orbit, five others have been observed which
belong apparently to the same cluster. These are the comets of 1585,
1743 I., 1766 II., 1783, and 1819 IV. "The fact that these comets have
not been re-observed on their successive returns through perihelion may
be explained either by the difficulty of observing them, owing to their
unfavorable positions, and to the circumstances of observers not
expecting their reappearance, their periodic character not being then
suspected, or because they may have been thrown by the disturbing action
of the larger planets into orbits such as to keep them continually out
of the range of view of terrestrial observers."[7]

  [7] Dr. Lardner.

Lexell's comet of 1770 is the most remarkable instance known of the
change produced in the orbits of these bodies by planetary attraction.
This comet passed so near Jupiter in 1779 that the attraction of the
latter was 200 times greater than that of the sun. The consequence was
that the comet, whose mean distance corresponded to a period of 5-1/2
years, was thrown into an orbit so entirely different that it has never
since been visible.


PETERS' COMET.

A telescopic comet was discovered by Dr. Peters on the 26th of June,
1846, which continued to be observed till the 21st of July. Its period,
according to the discoverer, is about 13 years, and its aphelion, like
that of Tuttle's comet, is in the vicinity of Saturn's orbit. It was
expected to return in 1859, and again in 1872, but each time escaped
detection, owing probably to the fact that its position was unfavorable
for observation.


STEPHAN'S COMET (1867 I.).

In January, 1867, M. Stephan, of Marseilles, discovered a new comet, the
elements of which, after two months' observations, were computed by Mr.
G. M. Searle, of Cambridge, Massachusetts. The perihelion of this body
is near the orbit of Mars; its aphelion near that of Uranus,--the least
distance of the orbits being about 2,000,000 miles. The present form of
the cometary path is doubtless due to the disturbing action of Uranus.
The comet completes its revolution in 33.62 years; consequently (as has
been pointed out by Mr. J. R. Hind) five of its periods are almost
exactly equal to two periods of Uranus. The next approximate appulse of
the two bodies will occur in 1985, when the form of the comet's orbit
may be sensibly modified.


ELLIPTIC COMETS WHOSE APHELIA ARE AT A MUCH GREATER DISTANCE THAN
NEPTUNE'S ORBIT.

In October, 1097, a comet was seen both in Europe and China, which was
noted for the fact of its having two distinct tails, making with each
other an angle of about 40 deg. From a discussion of the Chinese
observations (which extended through a longer period than the European),
Laugier concluded that this body is identical with the third comet of
1840, which was discovered by Galle on the 6th of March. If, therefore,
it has made no intermediate return without being observed, it must have
a period of about 743 years. It is also highly probable, from the
similarity of elements, that the comet which passed its perihelion on
the 5th of June, 1845, was a reappearance of the comet of 1596,--the
period of revolution being 249 years. The elements of the great comet of
1843 are somewhat uncertain. There is a probability, however, of the
identity of this body with the comet of 1668. This would make the period
175 years. The third comet of 1862 is especially interesting from its
connection with the August meteors. Its period, according to Dr.
Oppolzer, is 121-1/2 years.


THE GREAT COMET OF 1858

was one of the most remarkable in the nineteenth century. It was
discovered on the 2d of June, by Donati, of Florence, and first became
visible to the naked eye about the last of August. The comet attained
its greatest brilliancy about the 10th of October, when its distance
from the earth was 50,000,000 miles. The length of its tail somewhat
exceeded this distance. If, therefore, the comet had been at that time
directly between the sun and the earth, the latter must have been
enveloped for a number of hours in the cometic matter.

The observations of this comet during a period of five months enabled
astronomers to determine the elements of its orbit within small limits
of error. It completes a revolution, according to Newcomb, in 1854
years, in an orbit somewhat more eccentric than that of Halley's comet.
It will not return before the 38th century, and will only reach its
aphelion about the year 2800. Its motion per second when nearest the sun
is 36 miles; when most remote, only 234 yards.




CHAPTER IV.

OTHER REMARKABLE COMETS.


It remains to describe some of the most remarkable comets of which we
have any record, but of which we have no means of determining with
certainty whether they move in ellipses, parabolas, or hyperbolas.

In the year 466 B.C., a large comet appeared simultaneously with the
famous fall of meteoric stones near AEgospotamos. The former was supposed
by the ancients to have had some agency in producing the latter
phenomenon. Another of extraordinary magnitude appeared in the year 373
B.C. This comet was so bright as to throw shadows, and its tail extended
one-third of the distance from the horizon to the zenith. The years 156,
136, 130, and 48, before our era, were also signalized by the appearance
of very large comets. The apparent magnitude of the first of these is
said to have equaled that of the sun itself; while its light was
sufficient to diminish sensibly the darkness of the night. The second is
said to have filled a fourth part of the celestial hemisphere. The comet
of 130 B.C., sometimes called the comet of Mithridates, because of its
appearance about the time of his birth, is said to have rivaled the sun
in splendor.

In A.D. 178 a large comet was visible during a period of nearly three
months. Its nucleus had a remarkably red or fiery appearance, and the
greatest length of its tail exceeded 60 deg. The most brilliant comets of
the sixth century were probably those of 531 and 582. The train of the
latter, as seen in the west soon after sunset, presented the appearance
of a distant conflagration.

Great comets appeared in the years 975, 1264, and 1556. Of these, the
comet of 1264 had the greatest apparent magnitude. It was first seen
early in July, and attained its greatest brilliancy in the latter part
of August, when its tail was 100 deg. in length. It disappeared on the 3d of
October, about the time of the death of Pope Urban IV., of which event
the comet, in consequence of this coincidence, was considered the
precursor. These comets, on account of the similarity of their elements,
were believed by many astronomers to be the same, and to have a period
of about 300 years. In the case of identity, however, another
reappearance should have occurred soon after the middle of the
nineteenth century. As no such return was observed, we may conclude that
the comets were not the same, and that their periods are wholly unknown.

The comet discovered on the 10th of November, 1618, was one of the
largest in modern times; its tail having attained the extraordinary
length of 104 deg. The comet of 1652, so carefully observed by Hevelius,
almost equaled the moon in apparent magnitude. It shone, however, with a
lurid, dismal light. The tail of the comet of 1680 was 90 deg. in length.
This body is also remarkable for its near approach to the sun; its least
distance from the solar surface having been only 147,000 miles. It will
always be especially memorable, however, for having furnished Newton the
data by means of which he first showed that comets in their orbital
motions are governed by the same principle that regulates the planetary
revolutions.

Of all the comets which appeared during the eighteenth century, that
which passed its perihelion on the 7th of October, 1769, had the
greatest apparent magnitude. It was discovered by Messier on the 8th of
August, and continued to be observed till the 1st of December. On the
11th of September the length of its tail was 97 deg. The comet discovered
on the 26th of March, 1811, is in some respects the most remarkable on
record. It was observed during a period of 16 months and 22 days,--the
longest period of visibility known. On account of its situation with
respect to the earth, the apparent length of its tail was much less than
that of some other comets; its true length, however, was at one time
120,000,000 miles; and Sir William Herschel found that on the 12th of
October the greatest circular section of the tail was 15,000,000 miles
in diameter. The same astronomer found the diameter of the head of the
comet to be 127,000 miles, and that of the envelope at least 643,000. As
a general thing, the length of a comet-train increases very rapidly as
the body approaches the sun. But the perihelion distance of the comet of
1811 was considerably greater than the distance of the earth from the
sun; while its nearest approach to the earth was 110,000,000 miles. Its
true magnitude, therefore, has probably not been surpassed by any other
observed; and had its perihelion been very near the sun, it must have
exhibited an appearance of terrific grandeur. This comet has an elliptic
orbit, and its period, according to Argelander, is 3065 years.

The great comet of 1861 was discovered on the 13th of May, by Mr. John
Tebbut, Jr., of New South Wales. In this country, as well as in Europe,
it was first generally observed on the evening of June 30,--19 days
after its perihelion passage. Sir John Herschel, who observed it in
Kent, England, remarks that it far exceeded in brilliancy any comets he
had ever seen, not excepting those of 1811 and 1858. According to Father
Secchi, of the Collegio Romano, the length of its tail was 118 deg. This,
with a single exception,[8] is the greatest on record. The computed
orbit is elliptical; the period, 419 years.

  [8] The tail of the first comet of 1865 (observed in the
      Southern Hemisphere) attained the unprecedented length
      of 150 deg.--_M. N. R. A. S._, vol. xxv., p. 220.




CHAPTER V.

THE POSITION AND ARRANGEMENT OF COMETARY ORBITS.


The cosmical masses from which comets are derived seem to traverse in
great numbers the interstellar spaces. In consequence of the sun's
progressive motion, these nebulous bodies are sometimes drawn toward the
centre of our system. If, in this approach, they are not disturbed by
any of the large planets, they again recede in parabolas or hyperbolas.
When, however, as must sometimes be the case, they pass near Jupiter,
Saturn, Uranus, or Neptune, their orbits may be transformed into
elongated ellipses. The periodicity of many comets may thus be accounted
for.

In the present chapter it is proposed to consider the probable
consequences of the sun's motion through regions of space in which
cometary matter is widely diffused; to compare our theoretical
deductions with observed phenomena; and thus refer to their physical
cause a variety of facts which have hitherto received no satisfactory
explanation.[9]

  [9] This chapter is the substance of a paper read before the American
      Philosophical Society, November 19, 1869.

1. As comets, at least in many instances, owe their periodicity to the
disturbing action of the major planets, and as this planetary influence
is sometimes sufficient, especially in the case of Jupiter and Saturn,
to change the _direction_ of cometary motion, the great majority of
periodic comets should move in the same direction with the planets. Now,
of the comets known to be elliptical, 70 per cent. _have direct motion_.
In this respect, therefore, theory and observation are in striking
harmony.

2. When the relative positions of a comet and the disturbing planet are
such as to give the transformed orbit of the former a small perihelion
distance, the comet must return to the point at which it received its
greatest perturbation; in other words, to the orbit of the planet. The
aphelia of the comets of short period ought therefore to be found, for
the most part, _in the vicinity of the orbits of the major planets_.
This, as already shown in Chapters II. and III., is strikingly the case.
The actual distances of these aphelia, however, as compared with the
respective distances of Jupiter, Saturn, Uranus and Neptune, are
presented at one view in the following tables:


=I.= COMETS WHOSE APHELION DISTANCES ARE NEARLY EQUAL TO 5.20, THE
RADIUS OF JUPITER'S ORBIT.

  Comets.                  Aph. Dist.

   1. Encke's                4.09
   2. 1819 IV                4.81
   3. De Vico's              5.02
   4. Pigott's (1783)        5.28
   5. 1867 II                5.29
   6. 1743 I                 5.32
   7. 1766 II                5.47
   8. 1819 III               5.55
   9. Brorsen's              5.64
  10. D'Arrest's             5.75
  11. Faye's                 5.93
  12. Bicla's                6.19


=II.= COMETS WHOSE APHELION DISTANCES ARE NEARLY EQUAL TO 9.54, THE
RADIUS OF SATURN'S ORBIT.

  Comets.                     Aph. Dist.

  1. Peters' (1846 VI.)           9.45
  2. Tuttle's (1858 I.)          10.42


=III.= COMETS WHOSE APHELION DISTANCES ARE NEARLY EQUAL TO 19.18, THE
RADIUS OF URANUS'S ORBIT.

  Comets.                      Aph. Dist.

  1. 1867 I                      19.28
  2. November meteors            19.65
  3. 1866 I                      19.92


=IV.= COMETS WHOSE APHELION DISTANCES ARE NEARLY EQUAL TO 30.04, THE
RADIUS OF NEPTUNE'S ORBIT.

  Comets.                       Aph. Dist.

  1. Westphal's (1852 IV.)        31.97
  2. Pons' (1812)                 33.41
  3. Olbers' (1815)               34.05
  4. De Vico's (1846 IV.)         34.35
  5. Brorsen's (1847 V.)          35.07
  6. Halley's[10]                 35.37

  [10] Halley's comet _in aphelio_ is too remote from the plane of
       the ecliptic to be much disturbed by Neptune. Has the original
       position of the orbit been changed by Jupiter's influence?

The coincidences here pointed out (some of which have been noticed by
others) appear, then, to be necessary consequences of the motion of the
solar system through spaces occupied by meteoric nebulae. Hence the
observed facts receive an obvious explanation.

In regard to comets of long period we have only to remark that, for
anything we know to the contrary, there may be causes of perturbation
far exterior to the orbit of Neptune.

3. From what we observe in regard to the _larger_ bodies of the
universe--a clustering tendency being everywhere apparent,--it seems
highly improbable that cometic matter should be uniformly distributed in
the sidereal spaces. We would expect, on the contrary, to find it
collected in groups or clusters. This view is also in remarkable harmony
with the facts of observation. In 150 years, from 1600 to 1750, 16
comets were visible to the naked eye; of which 8 appeared in the 25
years from 1664 to 1689. Again, during 60 years, from 1750 to 1810, only
5 comets were visible to the naked eye, while in the next 50 years there
were double that number. The probable cause of such variations is
sufficiently obvious. As the sun in its progressive motion approaches a
cometary group, the latter is drawn toward the centre of our system; the
nearer members with greater velocity than the more remote. Those of the
same cluster would enter the solar domain at periods not very distant
from each other; the forms of their orbits depending upon their original
relative positions with reference to the sun's course, and also on
planetary perturbations. It is evident also that the passage of the
solar system through a region of space comparatively destitute of
cometic clusters would be indicated by a corresponding paucity of
comets.

4. The line of apsides of a large proportion of comets will be
approximately coincident with the solar orbit. The point towards which
the sun is moving is in longitude about 260 deg. The quadrants bisected by
this point and that directly opposite extend from 215 deg. to 305 deg., and from
35 deg. to 125 deg. The number of cometary perihelia found in these quadrants
up to July, 1868 (periodic comets being counted but once) was 159, or
62 per cent.; in the other two quadrants, 98, or 38 per cent.

This tendency of the perihelia to crowd together in two opposite regions
has been noticed by different writers.

5. Comets whose positions before entering our system were very remote
from the solar orbit must have _overtaken_ the sun in its progressive
motion; hence their perihelia must fall, for the most part, in the
vicinity of the point towards which the sun is moving; and they must in
general have very small perihelion distances. Now, what are the observed
facts in regard to the longitudes of the perihelia of the comets which
have approached within the least distance of the sun's surface? But
three have had a perihelion distance less than 0.01. _All_ these, it
will be seen by the following table, have their perihelia in close
proximity to the point referred to:


=I.= COMETS WHOSE PERIHELION DISTANCES ARE LESS THAN 0.01.

        Perihelion Passage.       Per. Dist.    Long. of Per.

  1. 1668, Feb.  28_d._ 13_h._     0.0047         277 deg.  2'
  2. 1680, Dec.  17     23         0.0062         262  49
  3. 1843, Feb.  27      9         0.0055         278  39

In Table II. all but the last have their perihelia in the same quadrant.


=II.= COMETS WHOSE PERIHELION DISTANCES ARE GREATER THAN 0.01 AND LESS
THAN 0.05.

         Perihelion Passage.       Per. Dist.    Long. of Per.

  1. 1689, Nov    29_d._ 4_h._      0.0189         269 deg. 41'
  2. 1816, March   1     8          0.0485         267  35
  3. 1826, Nov    18     9          0.0268         315  31
  4. 1847, March  30     6          0.0425         276   2
  5. 1865, Jan    14     7          0.0260.        141  15

The perihelion of the first comet in Table III. is remote from the
direction of the sun's motion; that of the second is distant but 14 deg.,
and of the third 21 deg.


=III.= COMETS WHOSE PERIHELION DISTANCES ARE GREATER THAN 0.05 AND LESS
THAN 0.1.

      Perihelion Passage.             Per. Dist.    Long. of Per.

  1. 1593, July    18_d._ 13_h._       0.0891         176 deg. 19'
  2. 1780, Sept.   30     22           0.0963         246  35
  3. 1821, March   21     12           0.0918         239  29

With greater perihelion distances the tendency of the perihelia to crowd
together round the point indicated is less distinctly marked.

6. Few comets of small perihelion distance should have their perihelia
in the vicinity of longitude 80 deg., the point opposite that towards which
the sun is moving. Accordingly we find, by examining a table of cometary
elements, that with a perihelion distance less than 0.1 there is not a
single perihelion between 35 deg. and 125 deg.; between 0.1 and 0.2 but 3; and
between 0.2 and 0.3 only 1.




CHAPTER VI.

THE DISINTEGRATION OF COMETS.


The _fact_ that in several instances meteoric streams move in orbits
identical with those of certain comets was first established by the
researches of Signor Schiaparelli. The _theory_, however, of an intimate
relationship between comets and meteors was advocated by the writer as
long since as 1861,[11]--several years previous to the publication of
Schiaparelli's memoirs. In the essay here referred to it was
maintained--

  [11] Danville Quarterly Review, December, 1861.

1. That meteors and meteoric rings "are the _debris_ of ancient but now
disintegrated comets whose matter has become distributed around their
orbits."

2. That the separation of Biela's comet as it approached the sun in
December, 1845, was but one in a series of similar processes which would
probably continue until the individual fragments would become invisible.

3. That certain luminous meteors have entered the solar system from the
interstellar spaces.[12]

  [12] Others, it was supposed, might have originated within the
       system,--a view which the writer has not wholly abandoned.

4. That the orbits of some meteors and periodic comets have been
transformed into ellipses by planetary perturbation; and

5. That numerous facts--some observed in ancient and some in modern
times--have been decidedly indicative of cometary disintegration.

What was thus proposed as theory has been since confirmed as undoubted
facts. When the hypothesis was originally advanced, the data required
for its mathematical demonstration were entirely wanting. The evidence,
however, by which it was sustained was sufficient to give it a high
degree of probability.

The existence of a divellent force by which comets near their perihelia
have been separated into parts is clearly shown by the following facts.
Whether this force, as suggested by Schiaparelli, is simply the unequal
attraction of the sun on different parts of the nebulous mass, or
whether, in accordance with the views of other astronomers, it is to be
regarded as a cosmical force of repulsion, is a question left for future
discussion.


HISTORICAL FACTS.

1. Seneca informs us that Ephoras, a Greek writer of the fourth century
before Christ had recorded the singular fact of a comet's separation
into two distinct parts.[13] This statement was deemed incredible by the
Roman philosopher, inasmuch as the occurrence was then without a
parallel. More recent observations of similar phenomena leave no room to
question the historian's veracity.

  [13] "Quaest. Nat.," lib. vii., cap. xvi.

2. The head of the great comet of A.D. 389, according to the writers of
that period, was "composed of several small stars." (Hind's "Comets," p.
103.)

3. On June 27, A.D. 416, two comets appeared in the constellation
Hercules, and pursued nearly the same apparent path. Probably at a
former epoch the pair had constituted a single comet.[14]

  [14] Chambers' "Descr. Astr.," p. 374.

4. On August 4, 813, "a comet was seen which resembled two moons joined
together." They subsequently separated, the fragments assuming different
forms.[15]

  [15] Ibid., p. 383.

5. The Chinese annals record the appearance of three comets--one large
and two smaller ones--at the same time, in the year 896 of our era.
"They traveled together for three days. The little ones disappeared
first, and then the large one."[16] The bodies were probably fragments
of a large comet which, on approaching the sun, had been separated into
parts a short time previous to the date of their discovery.

  [16] Ibid., p. 388.

6. _The third comet of 1618._--The great comet of 1618 exhibited decided
symptoms of disintegration. When first observed (on November 30), its
appearance was that of a lucid and nearly spherical mass. On the eighth
day the process of division was distinctly noticed, and on the 20th of
December it resembled a cluster of small stars.[17]

  [17] Hevelius, "Cometographia," p. 341. See also Grant's "Hist.
       of Phys. Astr.," p. 302.

7. _The comet of 1661._--The elements of the comets of 1532 and 1661
have a remarkable resemblance, and previous to the year 1790
astronomers regarded the bodies as identical. The similarity of the
elements is seen at a glance in the following table:

                                  Comet of 1532.   Comet of 1661.

  Longitude of perihelion           111 deg. 48'         115 deg. 16'
  Longitude of ascending node        87  23           81  54
  Inclination                        32  36           33   1
  Perihelion distance                0.5192           0.4427
  Motion                             Direct.          Direct.

The elements of the former are by Olbers; those of the latter by
Mechain. The return of the comet about 1790, though generally expected,
was looked for in vain. As a possible explanation of this fact, it is
interesting to recur to an almost forgotten statement of Hevelius. This
astronomer observed in the comet of 1661 an apparent breaking up of the
body into separate fragments.[18] The case may be analogous to that of
Biela's comet.

  [18] "Cometographia," p. 417.

8. The identity of the comets of 1866 and 1366, first suggested by
Professor H. A. Newton, is now unquestioned. The existence then of a
meteoric swarm, moving in the same track, is not the only evidence of
the original comet's partial dissolution. The comet of 1866 was
invisible to the naked eye; that of 1366, seen under nearly similar
circumstances, was a conspicuous object. The statement of the Chinese
historian that "it appeared nearly as large as a tow measure,"[19]
though somewhat indefinite, certainly justifies the conclusion that its
magnitude has greatly diminished during the last 500 years. The meteors
moving in the same orbit are doubtless the products of this gradual
separation.

  [19] Williams' "Chinese Observations of Comets," p. 73.

9. The repartition of Biela's comet in 1845, as well as the
non-appearance of the two fragments in 1865 and 1872,[20] were referred
to in a previous chapter.

  [20] One of the parts was seen at Madras, India, on the mornings of
       December 2 and 3, 1872.

The comet of Halley, if we may credit the descriptions given by ancient
writers, has been decreasing in brilliancy from age to age. The same is
true in regard to several others believed to be periodic. The comet of
A.D. 1097 had a tail 50 deg. long. At its return, in March, 1840, the length
of its tail was only 5 deg. The third comet of 1790 and the first of 1825
are supposed, from the similarity of their elements, to be identical.
Each perihelion passage occurred in May, yet the tail at the former
appearance was 4 deg. in length, at the latter but 2-1/2 deg. Other instances
might be specified of this apparent gradual dissolution. It would seem,
indeed, extremely improbable that the particles driven off from comets
in their approach to the sun, forming tails extending millions of miles
from the principal mass, should again be collected around the same
nuclei.

The fact, then, that meteors move in the same orbits with comets is but
a consequence of that disruptive process so clearly indicated by the
phenomena described. In this view of the subject, comets--even such as
move in elliptic orbits--are not to be regarded as permanent members of
the solar system. Their _debris_ becomes gradually scattered around the
orbit. Some parts of the nebulous ring will be more disturbed than
others by planetary perturbation. Portions of such streams as nearly
intersect the earth's path sometimes penetrate the atmosphere. Their
rapid motion renders them luminous. If very minute, they are burnt up or
dissipated without leaving any solid deposit; we then have the phenomena
of _shooting-stars_. When, however, as is sometimes the case, they
contain a considerable quantity of solid matter, they reach the earth's
surface as _meteoric stones_.




II.

METEORS.




CHAPTER VII.

METEORIC STONES.


Although numerous instances of the fall of aerolites had been recorded,
some of them apparently well authenticated, the occurrence long appeared
too marvelous and improbable to gain credence with scientific men. Such
a shower of rocky fragments occurred, however, on the 26th of April,
1803, at L'Aigle, in France, as forever to dissipate all doubt on the
subject. Similar displays since that time have been frequently
witnessed;--indeed scarcely a year passes without the fall of meteoric
stones in some part of the earth, either singly or in clusters. It would
not comport with the design of the present treatise to give an extended
list of these phenomena. The following account, however, includes the
most important instances in which the fall of meteoric stones has been
actually observed:

(1.) 1478 B.C.--According to the celebrated Parian chronicle, an
aerolite, or _thunder-stone_, as it was called, fell in the island of
Crete, about 1478 years before the Christian era. This is undoubtedly
the most ancient stone-fall on record. Meteoric masses have been
_found_, however, the fall of which _probably_ occurred at an epoch
still more ancient.

(2.) 1200 B.C.--A number of stones, which were anciently preserved in
Orchomenos, a town of Boeotia, were said to have fallen from heaven
about twelve centuries before our era.

(3.) 1168 B.C.--A mass of iron, as we learn from the Parian chronicle,
was seen to descend upon Mount Ida, in Crete.

(4.) 654 B.C.--According to Livy, a number of meteoric stones fell on
the Alban Hill, near Rome, about the year 654 B.C.

(5.) 616 B.C., _January_ 14.--It is related in the Chinese annals that
on the 14th of January, 616 B.C., a meteoric stone-fall broke several
chariots and killed ten men.

(6.) 466 B.C.--A mass of rock, described as "of the size of two
millstones," fell at AEgospotamos, in Thrace. An attempt to rediscover
this meteoric mass, so celebrated in antiquity, was recently made, but
without success. Notwithstanding this failure, Humboldt expressed the
hope that, as such a body would be difficult to destroy, it may yet be
found, "since the region in which it fell is now become so easy of
access to European travelers."

(7.) 465 B.C.--The famous stone called the "Mother of the Gods," and
which is described or alluded to by many ancient writers, was said to
have fallen from the skies. The poet Pindar was seated on a hill at the
time of its descent, and the meteorite struck the earth near his feet.
The stone, as it fell, was _encircled by fire_. "It is said to have been
of moderate dimensions, of a black hue, of an irregular, angular shape,
and of a metallic aspect. An oracle had predicted that the Romans would
continue to increase in prosperity if they were put in possession of
this precious deposit; and Publius Scipio Nasico was accordingly deputed
to Attalus, King of Pergamus, to obtain and receive the sacred idol,
whose worship was instituted at Rome 204 years before the Christian
era."--_Edinburgh Encyclopedia._

(8.) A.D. 921.--An immense aerolite fell into the river (a branch of the
Tiber) at Narni, in Italy. It projected three or four feet above the
surface of the water.

(9.) 1492, _November_ 7.--An aerolite, weighing 276 pounds, fell at
Ensisheim, in Alsace, penetrating the earth to the depth of three feet.
This stone, or the greater part of it, may still be seen at Ensisheim.

(10.) 1511, _September_ 14.--At noon an almost total darkening of the
heavens occurred at Crema. "During this midnight gloom," says a writer
of that period, "unheard-of thunders, mingled with awful lightnings,
resounded through the heavens.... On the plain of Crema, where never
before was seen a stone the size of an egg, there fell pieces of rock of
enormous dimensions and of immense weight. It is said that ten of these
were found, weighing 100 pounds each." A monk was struck dead at Crema
by one of these rocky fragments. This terrific display is said to have
lasted two hours, and 1200 aerolites were subsequently found.

(11.) 1637, _November_ 29.--A stone, weighing 54 pounds, fell on Mount
Vaison, in Provence.

(12.) 1650, _March_ 30.--A Franciscan monk was killed at Milan by the
fall of a meteoric stone.

(13.) 1674.--Two Swedish sailors were killed on shipboard by the fall of
an aerolite.

(14.) 1751, _May_ 26.--Two meteoric masses, consisting almost wholly of
iron, fell near Agram, the capital of Croatia. The larger fragment,
which weighs 72 pounds, is now in Vienna.

(15.) 1790, _July_ 24.--Between 9 and 10 o'clock at night a very large
meteor was seen near Bordeaux, France. Over Barbotan a loud explosion
was heard, which was followed by a shower of meteoric stones of various
magnitudes.

(16.) 1794, _July_.--A fall of about a dozen aerolites occurred at
Sienna, Tuscany.

(17.) 1795, _December_ 13.--A large meteoric stone fell near Wold
Cottage, in Yorkshire, England. "Several persons heard the report of an
explosion in the air, followed by a hissing sound; and afterward felt a
shock, as if a heavy body had fallen to the ground at a little distance
from them. One of these, a plowman, saw a huge stone falling toward the
earth, eight or nine yards from the place where he stood. It threw up
the mould on every side; and after penetrating through the soil, lodged
some inches deep in solid chalk-rock. Upon being raised, the stone was
found to weigh 56 pounds. It fell in the afternoon of a mild, but hazy
day, during which there was no thunder or lightning; and the noise of
the explosion was heard through a considerable district."--_Milner's
Gallery of Nature_, p. 134.

(18.) 1796, _February_ 19.--A stone of 10 pounds' weight fell in
Portugal.

(19.) 1803, _April_ 26.--This remarkable shower was referred to on a
previous page. At 1 o'clock P.M., the heavens being almost cloudless, a
tremendous noise, like that of thunder, was heard, and at the same time
an immense fire-ball was seen moving with great rapidity through the
atmosphere. This was followed by a violent explosion, which lasted
several minutes, and which was heard not only at L'Aigle, but in every
direction around it to the distance of 70 miles. Immediately after, a
great number of meteoric stones fell to the earth, generally penetrating
to some distance beneath the surface. Nearly 3000 of these fragments
were found and collected, the largest weighing about 17 pounds. The
occurrence very naturally excited great attention. M. Biot, under the
authority of the government, repaired to the place, collected the
various facts in regard to the phenomenon, took the testimony of
witnesses, etc., and finally embraced the results of his investigations
in an elaborate memoir.

(20.) 1807, _December_ 14.--A large meteor exploded over Weston,
Connecticut. The height, direction, velocity and magnitude of this body
were discussed by Dr. Bowditch in a memoir communicated to the American
Academy of Arts and Sciences in 1815. The appearance of the meteor
occurred about 6h. 15m. A.M.,--just after daybreak. Its apparent
diameter was half that of the full moon; its time of flight, about 30
seconds. Within less than a minute from the time of its disappearance
three distinct reports, like those of artillery, were heard over an area
several miles in diameter. Each explosion was followed by the fall of
meteoric stones. Unlike most aerolites, these bodies when first found
were so soft as to be easily pulverized between the fingers. On
exposure to the air, however, they gradually hardened. The weight of the
largest fragment was 35 pounds.

(21.) 1859, _November_ 15.--Between 9 and 10 o'clock in the morning an
extraordinary meteor was seen in several of the New England States, New
York, New Jersey, the District of Columbia, and Virginia. The apparent
diameter of the head was nearly equal to that of the sun, and it had a
train, notwithstanding the bright sunshine, several degrees in length.
Its disappearance on the coast of the Atlantic was followed by a series
of the most terrific explosions. It is believed to have descended into
the water, probably into Delaware Bay. A highly interesting account of
this meteor, by Professor Loomis, may be found in the _American Journal
of Science and Arts_ for January, 1860.

(22.) 1860, _May_ 1.--About 20 minutes before 1 o'clock, P.M., a shower
of meteoric stones fell in the southwest corner of Guernsey county,
Ohio. Full accounts of the phenomena are given in _Silliman's Journal_
for July, 1860, and January and July, 1861, by Professors E. B. Andrews,
E. W. Evans, J. L. Smith, and D. W. Johnson. From these interesting
papers we learn that the course of the meteor was about 40 deg. west of
north. Its visible track was over Washington and Noble counties, and the
prolongation of its projection, on the earth's surface, passes directly
through New Concord, in the southeast corner of Muskingum county. The
meteor when first seen was about 40 miles from the earth's surface. The
sky, at the time, was for the most part covered with clouds over
northwestern Ohio, so that if any portion of the meteoric mass
continued on its course it was invisible. The velocity of the meteor, in
relation to the earth's surface, was from three to four miles per
second; and hence its absolute velocity in the solar system must have
been somewhat greater than that of the earth.

"At New Concord,[21] Muskingum county, where the meteoric stones fell,
and in the immediate neighborhood, there were many distinct and loud
reports heard. At New Concord there was first heard in the sky, a little
southeast of the zenith, a loud detonation, which was compared to that
of a cannon fired at the distance of half a mile. After an interval of
ten seconds, another similar report. After two or three seconds another,
and so on with diminishing intervals. Twenty-three distinct detonations
were heard, after which the sounds became blended together and were
compared to the rattling fire of an awkward squad of soldiers, and by
others to the roar of a railway train. These sounds, with their
reverberations, are thought to have continued for two minutes. The last
sounds seemed to come from a point in the southeast 45 deg. below the
zenith. The result of this cannonading was the falling of a large number
of stony meteorites upon an area of about 10 miles long by 3 wide. The
sky was cloudy, but some of the stones were seen first as 'black
specks', then as 'black birds', and finally falling to the ground. A few
were picked up within 20 or 30 minutes. The warmest was no warmer than
if it had lain on the ground exposed to the sun's rays. They penetrated
the earth from two to three feet. The largest stone, which weighed 103
pounds, struck the earth at the foot of a large oak-tree, and, after
cutting off two roots, one five inches in diameter, and grazing a third
root, it descended two feet ten inches into hard clay. This stone was
found resting under a root that was not cut off. This would seemingly
imply that it entered the earth obliquely."

  [21] New Concord is close to the Guernsey county line. Nearly all
       the stones fell in Guernsey.

Over thirty of the stones which fell were discovered, while doubtless
many, especially of the smaller, being deeply buried beneath the soil,
entirely escaped observation. The weight of the largest ten was 418
pounds.

(23.) 1860, _July_ 14.--About 2 o'clock P.M. on the 14th of July, 1860,
a shower of aerolites fell at Dhurmsala, in India. The fall was attended
by a tremendous detonation, which greatly terrified the inhabitants of
the district. The natives, supposing the stones to have been thrown by
some of their deities from the summit of the Himalayas, carried off many
fragments to be kept as objects of religious veneration. Lord Canning
and Mr. J. R. Saunders succeeded, however, in obtaining numerous
specimens, which they forwarded to the British Museum and several
European cabinets. They are earthy aerolites, of a specific gravity
somewhat greater than that of granite.

(24.) 1864, _May_ 14.--Early in the evening a very large and brilliant
meteor was seen in France, from Paris to the Spanish border. At
Montauban and in the vicinity loud explosions were heard, which were
followed by showers of meteoric stones near the villages of Orgueil and
Nohic. The principal facts in regard to the meteor are the following:

  Elevation when first seen, over                 55 miles
      "     at the time of its explosion          20   "
  Inclination of its path to the horizon          20 deg. or 25 deg.
  Velocity per second, about                      20 miles,
               or equal to that of the earth's orbital motion.

"This example," says Professor Newton, "affords the strongest proof that
the detonating and stone-producing meteors are phenomena not essentially
unlike."

(25.) 1868, _January_ 30.--It is obviously a matter of much importance
that the composition and general characteristics of aerolites, together
with the phenomena attending their fall, should be carefully noted; as
such facts have a direct bearing on the theory of their origin. In this
regard the memoirs of Professors J. G. Galle, of Breslau, and G. vom
Rath, of Bonn, on a meteoric fall which occurred at Pultusk, Poland, on
the 30th of January, 1868, have more than ordinary interest. These
memoirs establish the fact that the aerolites of the Pultusk shower
_entered our atmosphere_ as a swarm or cluster of distinct meteoric
masses. It is shown, moreover, by Dr. Galle that this meteor-group had a
proper motion when it entered the solar system of at least from 4-1/2 to
7 miles per second.

The foregoing list contains but a small proportion of the meteoric
stones whose fall has been actually observed. But, besides these, other
masses have been found so closely similar in structure to aerolites
whose descent has been witnessed, as to leave no doubt in regard to
their origin. One of these is a mass of iron and nickel, weighing 1680
pounds, found by the traveler Pallas, in 1749, at Abakansk, in Siberia.
This immense aerolite may be seen in the Imperial Museum at St.
Petersburg. On the plain of Otumpa, in Buenos Ayres, is a meteoric mass
7-1/2 feet in length, partly buried in the ground. Its estimated weight
is about 16 tons. A specimen of this stone, weighing 1400 pounds, has
been removed and deposited in one of the rooms of the British Museum. A
similar block, of meteoric origin, weighing more than six tons, was
discovered some years since in the province of Bahia, in Brazil.


GENERAL REMARKS.

1. A Committee on Luminous Meteors was appointed several years since by
the British Association for the Advancement of Science. This committee,
consisting at present of James Glaisher, F.R.S., Robert P. Greg, F.R.S.,
Alexander S. Herschel, F.R.A.S., and Charles Brooke, F.R.S., report from
year to year not only their own observations on aerolites, fire-balls,
and falling stars, but also such facts bearing upon the subject as can
be derived from other sources. An analysis of these reports justifies
the conclusion that meteoric stone-falls, like star-showers, occur with
greater frequency than usual on or about particular days. These epochs,
established with more or less certainty, are the following:

  (_a._) January         4th.
  (_b._)    "           16th.
  (_c._)    "           29th.
  (_d._) February       10th.
  (_e._)    "     15th--18th.
  (_f._) March           6th.
  (_g._)   "            12th.
  (_h._) April           1st.
  (_i._)   "      10th--14th.
  (_j._) May        8th--9th.
  (_k._)  "       13th--14th.
  (_l._)  "       17th--19th.
  (_m._) June             3d.
  (_n._)  "              9th.
  (_o._)  "             12th.
  (_p._)  "             16th.
  (_q._) July        3d--4th.
  (_r._)  "       14th--17th.
  (_s._) August     5th--7th.
  (_t._)   "            11th.
  (_u._) September 4th--10th.
  (_v._) October        13th.
  (_w._) November        5th.
  (_x._)   "      12th--13th.
  (_y._)   "      27th--30th.
  (_z._) December        5th.
  (_z'._)   "      8th--14th.
  (_z''._)  "           27th.

2. It is worthy of remark that no new elements have been found in
meteoric stones. Humboldt, in his "Cosmos," called attention to this
interesting fact. "I would ask," he remarks, "why the elementary
substances that compose one group of cosmical bodies, or one planetary
system, may not in a great measure be identical? Why should we not adopt
this view, since we may conjecture that those planetary bodies, like all
the larger or smaller agglomerated masses revolving round the sun, have
been thrown off from the once far more expanded solar atmosphere, and
have been formed from vaporous rings describing their orbits round the
central body?"

3. But while aerolites contain no elements but such as are found in the
earth's crust, the manner in which these elements are combined and
arranged is so peculiar that a skillful mineralogist will readily
distinguish them from terrestrial substances.

4. Of the eighteen or nineteen elements hitherto observed in meteoric
stones, iron is found in the greatest abundance. The specific gravities
vary from 1.94 to 7.901: the former being that of the stone of Alais;
the latter that of the meteorite of Wayne county, Ohio, described by
Professor J. L. Smith in _Silliman's Journal_ for November, 1864, p.
385.

5. The average number of aerolitic falls in a year was estimated by
Schreibers at 700. Baron Reichenbach, however, after a discussion of the
data at hand, makes the number much larger. He regards the probable
annual average for the entire surface of the earth as not less than
4500. This would give twelve daily falls. They are of every variety as
to magnitude, from a weight of less than a single ounce to over fifteen
tons. The baron even suspects the meteoric origin of large masses of
dolerite which all former geologists had considered native to our
planet.

6. An analysis of any extensive table of meteorites and fire-balls
proves that a greater number of aerolitic falls have been observed
during the months of June and July, when the earth is near its aphelion,
than in December and January, when near its perihelion. It is found,
however, that the reverse is true in regard to bolides, or fire-balls.
These facts are susceptible of an obvious explanation. The fall of
meteoric stones would be more likely to escape observation by night than
by day, on account of the relatively small number of observers. But the
days are shortest when the earth is in perihelion, and longest when in
aphelion; the ratio of their lengths being nearly equal to that of the
corresponding numbers of aerolitic falls. On the other hand, it is
obvious that fire-balls, unless very large, would not be visible during
the day. The _observed_ number will therefore be greatest when the
nights are longest; that is, when the earth is near its perihelion.
This, it will be found, is precisely in accordance with observation.




CHAPTER VIII.

SHOOTING-STARS.--METEORS OF NOVEMBER 14.


Although shooting-stars have doubtless been observed in all ages of the
world, it is only within the last half century that they have attracted
the special attention of scientific men. A few efforts had been made to
determine the height of such meteors, but the first general interest in
the subject was excited by the brilliant meteoric display of November
13, 1833. This shower of fire can never be forgotten by those who
witnessed it. The meteors were observed from the West Indies to British
America, and from 60 deg. to 100 deg. west longitude from Greenwich. As early as
10 o'clock on the evening of the 12th shooting-stars were observed with
unusual frequency; their motions being generally westward. Soon after
midnight their numbers became so extraordinary as to attract the
attention of all who happened to be in the open air. The meteors,
however, became more and more numerous till 4, or half past 4, o'clock;
and the fall did not entirely cease till ten minutes before sunrise.
From 2 to 6 o'clock the numbers were so great as to defy all efforts at
counting them; while their brilliancy was such that persons sleeping in
rooms with uncurtained windows were aroused by their light. The meteors
varied in apparent magnitude from the smallest visible points to
fire-balls equaling the moon in diameter. Occasionally one of the larger
class would separate into several parts, and in some instances a
luminous train remained visible for three or four minutes. No sound
whatever accompanied the display. It was noticed by many observers that
all the meteors diverged from a point near the star _Gamma Leonis_; in
other words, their paths if traced backward would intersect each other
at a particular locality in the constellation Leo. In some parts of the
country the inhabitants were completely terror-stricken by the
magnificence of the display. In the afternoon of the day on which the
shower occurred the writer met with an illiterate farmer who, after
describing the phenomena as witnessed by himself, remarked that "the
stars continued to fall till none were left," and added, "I am anxious
to see how the heavens will appear this evening; I believe we shall see
no more stars." A gentleman of South Carolina described the effect on
the <DW64>s of his plantation as follows:--"I was suddenly awakened by
the most distressing cries that ever fell on my ears. Shrieks of horror
and cries for mercy I could hear from most of the <DW64>s of the three
plantations, amounting in all to about 600 or 800. While earnestly
listening for the cause I heard a faint voice near the door, calling my
name. I arose, and, taking my sword, stood at the door. At this moment I
heard the same voice still beseeching me to arise, and saying, 'O my
God, the world is on fire!' I then opened the door, and it is difficult
to say which excited me the most,--the awfulness of the scene, or the
distressed cries of the <DW64>s. Upwards of a hundred lay prostrate on
the ground,--some speechless, and some with the bitterest cries, but
with their hands raised, imploring God to save the world and them. The
scene was truly awful; for never did rain fall much thicker than the
meteors fell towards the earth; east, west, north, and south, it was the
same."

At the time of this wonderful meteoric display Captain Hammond, of the
ship _Restitution_, had just arrived at Salem, Massachusetts, where he
observed the phenomenon from midnight till daylight. He recollected with
astonishment that precisely one year before, viz., on the 13th of
November, 1832, he had observed a similar appearance (although the
meteors were less numerous) at Mocha, in Arabia. It was found, moreover,
as a further and most remarkable coincidence, that an extraordinary fall
of meteors had been witnessed on the 12th of November, 1799. This was
seen and described by Andrew Ellicott, Esq., who was then at sea near
Cape Florida. It was also observed by Humboldt and Bonpland, in Cumana,
South America. Baron Humboldt's description of the shower is as
follows:--"From half after two, the most extraordinary luminous meteors
were seen toward the east. Thousands of bolides and falling stars
succeeded each other during four hours. They filled a space in the sky
extending from the true east 30 deg. toward the north and south. In an
amplitude of 60 deg. the meteors were seen to rise above the horizon at
E.N.E. and at E., describe arcs more or less extended, and fall toward
the south, after having followed the direction of the meridian. Some of
them attained a height of 40 deg., and all exceeded 25 deg. or 30 deg. Mr. Bonpland
relates, that from the beginning of the phenomenon there was not a space
in the firmament equal in extent to three diameters of the moon, that
was not filled at every instant with bolides and falling stars. The
Guaiqueries in the Indian suburb came out and asserted that the firework
had begun at one o'clock. The phenomenon ceased by degrees after four
o'clock, and the bolides and falling stars became less frequent; but we
still distinguished some toward the northeast a quarter of an hour after
sunrise."

This wonderful correspondence of dates excited a very lively interest
throughout the scientific world. It was inferred that a recurrence of
the phenomenon might be expected, and accordingly arrangements were made
for systematic observations on the 12th, 13th, and 14th of November. The
periodicity of the shower was thus, in a very short time, placed wholly
beyond question. The facts in regard to the phenomena of November 13,
1833, were collected and discussed by Olmsted, Twining, and other
astronomers. The inquiry, however, very naturally arose whether any
trace of the same meteoric group could be found in ancient times. To
determine this question many old historical records were ransacked by
the indefatigable scientist, Edward C. Herrick, in our own country, and
by Arago, Quetelet, and others, in Europe. These examinations led to the
discovery of ten undoubted returns of the November shower previous to
that of 1799. The descriptions of these former meteoric falls are given
by Professor H. A. Newton in the _American Journal of Science_, for May,
1864. They occurred in the years 902, 931, 934, 1002, 1101, 1202, 1366,
1533, 1602, and 1698. Historians represent the meteors of A.D. 902 as
innumerable, and as moving like rain in all directions. The exhibition
of 1202 was scarcely less magnificent. "On the last day of Muharrem,"
says a writer of that period, "stars shot hither and thither in the
heavens, eastward and westward, and flew against one another like a
scattering swarm of locusts, to the right and left; this phenomenon
lasted until daybreak; people were thrown into consternation, and cried
to God the Most High with confused clamor." The shower of 1366 is thus
described in a Portuguese chronicle, quoted by Humboldt: "In the year
1366, twenty-two days of the month of October being past, three months
before the death of the king, Don Pedro (of Portugal), there was in the
heavens a movement of stars such as men never before saw or heard of. At
midnight, and for some time after, all the stars moved from the east to
the west; and after being collected together, they began to move, some
in one direction and others in another. And afterward they fell from the
sky in such numbers, and so thickly together, that as they descended low
in the air they seemed large and fiery, and the sky and the air seemed
to be in flames, and even the earth appeared as if ready to take fire.
That portion of the sky where there were no stars seemed to be divided
into many parts, and this lasted for a long time."


The Showers of 1866-9.

The fact that all great displays of the November meteors have taken
place at intervals of 33 or 34 years, or some multiple of that period,
had led to a general expectation of a brilliant shower in 1866. In this
country, however, the public curiosity was much disappointed.[22] The
numbers seen were greater than on ordinary nights, but not such as would
have attracted any special attention. The greatest number recorded at
any one station was seen at New Haven by Professor Newton. On the night
of the 12th 694 were counted in five hours and twenty minutes, and on
the following night, 881 in five hours. A more brilliant display was,
however, witnessed in Europe. Meteors began to appear in unusual
frequency about 11 o'clock on the night of the 13th, and their numbers
continued to increase with great rapidity for more than two hours; the
maximum being reached a little after 1 o'clock. A writer in Edinburgh,
Scotland, thus describes the phenomenon as observed at that
city:--"Standing on the Calton Hill, and looking westward,--with the
observatory shutting out the lights of Princes Street,--it was easy for
the eye to delude the imagination into fancying some distant enemy
bombarding Edinburgh Castle from long range; and the occasional
cessation of the shower for a few seconds, only to break out again with
more numerous and more brilliant drops of fire, served to countenance
this fancy. Again, turning eastward, it was possible now and then to
catch broken glimpses of the train of one of the meteors through the
grim dark pillars of that ruin of most successful manufacture, the
National Monument; and in fact from no point in or out of the city was
it possible to watch the strange rain of stars, pervading as it did all
points of the heavens, without pleased interest and a kindling of the
imagination, and often a touch of deeper feeling that bordered on awe."
At London about 1 o'clock a single observer counted 200 in two minutes.
The whole number seen at Greenwich was 8485. The shower was also
observed in different countries on the continent.

  [22] The first indication of the approaching shower was the appearance
       of meteors in unusual numbers at Malta, on the 13th of November,
       1864. In 1865, as observed at Greenwich and other stations, they
       were still more numerous.

In 1867 the display was generally observed throughout the United States.
From the able and interesting reports of Commodore Sands and Professors
Newcomb, Harkness, and Eastman, we derive the following facts in regard
to the shower as seen at Washington, D. C.:

  Commencement                  1_h._  0_m._ A.M. Nov. 14.
  Maximum                       4     20      "     "
  End                           5      0      "     "
  Number of meteors per hour at maximum      3000
  Mean height on first appearance      75 miles.
   "     "    on disappearance         55  "
  Position of radiant, R. A. 151 deg., Decl. 22-1/2 deg.

The shower of 1868 was in some respects quite remarkable, though the
number of meteors was less than in 1866 or 1867. At New Haven the fall
commenced about midnight, and from 2 o'clock till daybreak over 5000
meteors were counted. The time of maximum could not be accurately
determined, as no decrease in the numbers was observable till dawn. The
display was also witnessed in England and in Cape Colony, South Africa.
The times of maxima in these countries differed so materially as to
indicate a decided stratification of the meteoric stream. The entire
depth, moreover, where crossed by the earth in 1868, was much greater
than at the part traversed either in 1866 or 1867.

In 1869 the shower was observed at Port Said, Lower Egypt, by G. L.
Tupman, Esq.; in Florida, U. S., by Commander William Gibson, U.S.N.;
and at Santa Barbara, California, by Mr. G. Davidson and Mrs. E.
Davidson. The first observed 112 meteors in 1h. 54m., from 2h. 30m. to
4h. 24m., Alexandria mean time; the numbers during this interval being
nearly equal, though slightly decreasing. Throughout the morning
(November 14) the sky was only partly clear. The two observers at Santa
Barbara saw 556 in 2h. 25m., ending at 3h. 43m. A.M. In Florida also the
display was quite brilliant, though inferior to that of 1868. It should
be remarked that the morning in many parts of the United States was
cloudy. No considerable number of the meteors of this stream has been
observed in any part of the world since 1869.


DISCUSSION OF THE PHENOMENA.

Since the memorable display of November 13, 1833, the phenomena of
shooting-stars have been observed and discussed with a very lively
interest. Among the first laborers in this department of research the
names of Olmsted, Herrick, and Twining must ever hold a conspicuous
place. The fact that the position of the radiant point did not change
with the earth's rotation at once placed the cosmical origin of the
meteors wholly beyond question. The theory of a ring of nebulous matter
revolving round the sun in an elliptic orbit--a theory somewhat
different from that proposed by Olmsted--was found to afford a simple
and satisfactory explanation of the phenomena. This hypothesis of an
eccentric stream of meteors intersecting the earth's orbit was adopted
by Humboldt, Arago, and others, shortly after the occurrence of the
meteoric shower of 1833.

A few years previous to the display of 1866 it was shown by Professor
Newton, of Yale College, that the distribution of meteoric matter around
the ring or orbit is far from uniform; that the motion is retrograde;
that the node of the orbit has an annual forward motion of 102''.6 with
respect to the equinox, or of 52''.4 with respect to the fixed stars;
that the periodic time must be limited to five accurately determined
periods, viz.: 180.05 days, 185.54 days, 354.62 days, 376.5 days, or
33.25 years; and that the inclination of the orbit to the ecliptic is
about 17 deg. Professor Newton, for reasons assigned, regarded the third
period named as the most probable. He remarked, however, that by
computing the secular motion of the node for each periodic time, and
comparing the result with the known precession, it was possible to
determine which of the five periods is the correct one.

For the application of this crucial test,--a problem of more than
ordinary interest,--we are indebted to Professor J. C. Adams, of
Cambridge, England. By an elegant analysis it was first shown that for
either of the first four periods designated by Professor Newton, the
annual motion of the node, resulting from planetary perturbation, would
be considerably less than one half of the observed motion. It only
remained, therefore, to examine whether the period of 33-1/4 years would
give a motion of the node corresponding with observation. Professor
Adams found that in this time the longitude of the node is increased 20'
by the action of Jupiter, 7' by the action of Saturn, and 1' by that of
Uranus. The effect of the other planets is scarcely perceptible. The
_calculated_ motion in 33-1/4 years is therefore 28'. The _observed_
motion in the same time, according to Professor Newton, as previously
stated, is 29'. This remarkable accordance was at once accepted by
astronomers as satisfactory evidence that the period is about 33.25
years.

Having determined the periodic time, the mean distance, or semi-axis
major, is found by Kepler's third law to be 10.34. The aphelion is
consequently situated at a comparatively short distance beyond the orbit
of Uranus. The orbit is represented in Fig. 4.

[Illustration: Fig. 4.]

It was stated at the close of Chapter VI. that shooting-stars are the
dissevered fragments of cometic matter, which, penetrating our
atmosphere, are rendered luminous by the resistance so encountered. The
discovery that comets and meteors are actually moving in the same orbits
was first announced by Signor Schiaparelli in 1867. The coincidence of
the orbits of Tempel's comet[23] as computed by Dr. Oppolzer, and the
meteors of November 14 as determined by Schiaparelli, is too close to be
regarded as merely accidental. These elements are as follows:

                                  Nov. Meteors.       Tempel's Comet.
  Perihelion passage            Nov. 10.092, 1866.  Jan. 11.160, 1866.
  Passage of descending node    Nov. 13.576,
  Longitude of perihelion          56 deg. 26'              60 deg. 28'
  Longitude of ascending node     231 deg. 28'             231 deg. 26'
  Inclination                      17 deg. 44'              17 deg. 18'
  Perihelion distance               0.9873               0.9765
  Eccentricity                      0.9046               0.9054
  Semi-major axis                  10.3400              10.3240
  Periodic time                    33.2500 _y._         33.1760 _y._
  Motion                          Retrograde.          Retrograde.

  [23] See page 30.

The fact is thus obvious that the meteors of November 14 are the
products of the comet's gradual dissolution. It has been stated that the
comets of 1366 and 1866 are probably identical. The interval indicates a
period of 33.283 years--greater by 39 days than that found by Oppolzer.
With this value of the periodic time and the known secular variation of
the node it is found that the comet and Uranus were in close proximity
about the beginning of the year 547 B.C. It is therefore not improbable
that the former was then thrown into its present orbit by the attraction
of the latter. The celebrated Leverrier designated the year 126 of our
era as the probable epoch of the comet's entrance into our system. This
date, however, is incompatible with the period here adopted. It is
worthy of remark, moreover, as bearing on this question, that the
extension of the cluster in the tenth century, as indicated by the
showers of 902, 931, and 934, was too great to have been effected in so
short a period as 800 years.

With the period of 33.283 years it is easy to find that the comet will
make a near approach to the earth about the 16th or 17th of November,
1965, and to Uranus in 1983. At one of these epochs the cometary orbit
will probably undergo considerable transformation.

We have seen that the comet of 1866, and also the meteoroids following
in its path, have their perihelion at the orbit of the earth, and their
aphelion at the orbit of Uranus. Both planets, therefore, at each
encounter with the current not only appropriate a portion of the
meteoric matter, but entirely change the orbits of many meteoroids. In
regard to the devastation produced by the earth in passing through the
cluster, it is sufficient to state that, according to Weiss, the meteor
orbits resulting from the disturbance will have all possible periods
from 21 months to 390 years. It may be regarded, therefore, as evidence
of the recent[24] introduction of this meteor-stream into the solar
system that the comet of 1866, which constitutes a part of the cluster,
has not been deflected from the meteoric orbit by either the earth or
Uranus.

  [24] Recent in comparison with the origin of the August meteors,
       which constitute a continuous ring.




CHAPTER IX.

OTHER METEORIC STREAMS.


_The Meteors of August 7-11._--Muschenbroek, in his "Introduction to
Natural Philosophy," published in 1762, stated as the result of his own
observations that shooting-stars are more abundant in August than in any
other part of the year. The fact, however, that a maximum occurs on the
9th or 10th of the month was first shown by Quetelet in 1835. Since that
time the shower has been regularly observed both in Europe and America;
the number of meteors at the maximum sometimes amounting to 160 per
hour. Their tracks when produced backward intersect each other at a
particular point in the constellation Perseus.

Of the 315 meteoric displays given in Quetelet's catalogue, 63 belong to
the August epoch. Their dates up to the commencement of the present
century are as follows:

   1.      A.D. 811, July 25th.
   2.           820,  "   25th-30th.
   3.           824,  "   26th-28th.
   4.           830,  "   26th.
   5.           833,  "   27th.
   6.           835,  "   26th.
   7.           841,  "   25th-30th.
   8.           924,  "   27th-30th.
   9.           925,  "   27th-30th.
  10.           926,  "   27th-30th.
  11.           933,  "   25th-30th.
  12.          1243, Aug.  2d.
  13.          1451,  "    7th.
  14.          1709,  "    8th.
  15.          1779,  "    9th-10th.
  16.          1781,  "    8th.
  17.          1784,  "    6th-9th.
  18.          1789,  "   10th.
  19.          1798,  "    9th.
  20.          1799,  "    9th-10th.
  21.          1800,  "   10th.

As the earth is about five days in crossing the ring, its breadth in
some parts cannot be less than 8,000,000 miles.

In 1866 Professor Schiaparelli, on computing the orbit of this meteoric
stream, noticed the remarkable agreement of its elements with those of
Swift's or Tuttle's comet[25] (1862, III.), as computed by Dr. Oppolzer.
These coincidences are exhibited in the following table:

                              Meteors of      Comet III.
                               August 10.      of 1862.

  Longitude of perihelion      343 deg. 38'        344 deg. 41'
  Ascending node               138 deg. 16'        137 deg. 27'
  Inclination                   63 deg.  3'         66 deg. 25'
  Perihelion distance          0.9643          0.9626.
  Period                       105 years (?)   121.5 years.
  Motion                       Retrograde.     Retrograde.

  [25] Mr. Swift, of Marathon, N. Y., had two or three days priority
       in the discovery of this comet, but unfortunately delayed his
       announcement of the fact.

It appears, therefore, that the third comet of 1862 is a part of the
meteoric stream whose orbit is crossed by the earth on the 10th of
August.

The characteristics of different meteor-zones afford interesting
indications in regard to their relative age, the magnitude and
composition of their corpuscles, etc. Thus, if we compare the streams of
August 10 and November 14, we shall find that the former probably
entered our system at a comparatively remote epoch. We have seen that at
each return to perihelion the meteoric cluster is extended over a
greater arc of its orbit. Now, Tuttle's comet and the August meteors
undoubtedly constituted a single group previous to their entering the
solar domain. It is evident, however, from the annual return of the
shower during the last 90 years, that the ring is at present nearly if
not quite continuous. That the meteoric mass had completed many
revolutions before the ninth century of our era is manifest from the
frequent showers observed between the years 811 and 841. At the same
time, the long interval of 83 years between the last observed display in
the ninth century, and the first in the tenth, seems to indicate the
existence of a wide chasm in the ring no more than a thousand years
since.

Neither the period of the meteors nor that of the comet can yet be
regarded as accurately ascertained. The latter, however, in all
probability, exceeds the former by several years. Now, at each passage
of the earth through the elliptic stream, those meteoroids nearest the
disturbing body must be thrown into orbits differing more or less from
that of the primitive group. In like manner the near approach of the
_comet_ to the earth at an ancient epoch may account for the lengthening
of its periodic time.


The Meteors of November 27.

Professor Schiaparelli's brilliant discovery of the relation between
comets and meteors may now be ranked with the established truths of
astronomy. His hypothesis, however, in regard to the _origin_ of
meteoric streams has not been generally accepted. Comets and meteors,
according to his theory, are derived from cosmical clouds existing in
great numbers in stellar space. These nebulae, in consequence of their
own motion or that of the sun, are drawn towards the centre of our
system. By the unequal influence of the sun's attraction on different
parts, such clouds are transformed into currents of great length before
reaching the limits of the planetary system. Shooting-stars, fire-balls,
aerolites, and comets being all of the same nature, differing merely in
size, sometimes fall towards the sun as parts of the same current.

The views of Dr. Weiss, of Vienna, differ from those of Schiaparelli, in
that he regards comets as the original bodies by whose disintegration
meteor-streams are gradually formed.[26] "Cosmical clouds," he remarks,
"undoubtedly appear in the universe, but only of such density that in
most cases they possess sufficient coherence to withstand the
destructive operation of the sun's attraction, not only up to the
boundaries of our solar system, but even within it. Such cosmical clouds
will always appear to us as comets when they pass near enough to the
earth to become visible. Approaching the sun, the comet undergoes great
physical changes, which finally affect the stability of its structure:
it can no longer hold together: parts of it take independent orbits
around the sun, having great resemblance to the orbit of the parent
comet. With periodical comets, this process is repeated at each
successive approach to the sun. Gradually the products of disintegration
are distributed along the comet's orbit, and if the earth's orbit cuts
this, the phenomenon of shooting-stars is produced."

  [26] _Astr. Nach._, Nos. 1710, 1711. For a fuller statement of
       Schiaparelli's theory, see Silliman's Journal for May, 1867.

These views of the distinguished astronomer of Vienna are confirmed by
the star-shower of November 27, 1872. That the orbits of the earth and
Biela's comet intersect at the point passed by the former about the last
of November, and that in 1845 the comet separated into two visible
parts, has been stated in a previous chapter. The comet's non-appearance
in December, 1865, and in September, 1872, was regarded by astronomers
as presumptive evidence of its progressive dissolution. A meteoric
shower, resulting from the earth's collision with the cometary _debris_,
was accordingly expected about the 27th of November.

The first indication of the approaching display appeared on the evening
of November 24, when meteors in unusual numbers were observed by
Professor Newton, at New Haven, Connecticut. On Wednesday evening, the
27th, from the close of twilight till 8 o'clock, a decided shower of
shooting-stars was noticed in various parts of the United States. At
Greencastle, Indiana, Professor Joseph Tingley counted 110 meteors in 40
minutes, and at Princeton, in the same State, Mr. D. Eckley Hunter
counted 70 in 80 minutes. The numbers seen at New Haven were
considerably greater. The fact that the display commenced before
daylight had entirely closed seemed to indicate that only the
termination of the shower had been observed in this country. Accordingly
the display was soon found to have been witnessed from 60 deg. E. to 90 deg. W.
of Greenwich, or through 150 deg. of longitude. In England the first bolide
of the swarm was seen by M. M. Brinkley, at 3 o'clock, P.M., in full
daylight. The meteors were most numerous in the southern part of the
continent, particularly in Italy. At the Observatory of Breslau,
according to M. Faye, 3000 were seen from 6h. 30m. to 7h. 50m. Dr. Heis
reported that at Muenster 2500 per hour were counted by two observers. At
Naples, Signor Gasparis observed two meteors per second. At Turin, M.
Denza, Director of the Observatory, reported 33,400 in 6h. 30m.; many of
various and delicate colors, and followed by long and brilliant trains.
At some points the numbers were so great that an accurate enumeration
was wholly impossible. In short, the display was decidedly the most
brilliant that has occurred since that of November 13, 1833.

But some of the most interesting circumstances in connection with the
phenomena of November 27, 1872, remain to be detailed. Astronomers
without exception regarded the display as due to the earth's passage
through the _debris_ following in the path of Biela's comet. In
accordance with this view Dr. Klinkerfues, of Gottingen, concluded that
the comet itself, or rather its largest portion, ought to be found in
the region of the heavens nearly opposite to that from which the
meteoroids appeared to radiate.[27] As this point in the southern
hemisphere could not be observed in Europe, he conceived the happy idea
of detecting the fugitive _by means of the electric telegraph_. The
following was accordingly dispatched to Mr. Pogson, Director of the
Government Observatory at Madras, in Southern India: "_Biela touched
earth on 27th; search near Theta Centauri_." The first two mornings
after the receipt of this dispatch were cloudy at Madras. On the third,
however, the cometary fragment was found, and its motion accurately
measured. The observer described it as circular and rather bright, with
no traces of a tail. But one fragment could be detected. On the next
morning, December 3, the comet was again observed. Its diameter had
sensibly increased; it had a bright nucleus, and still presented a
circular aspect. A faint tail was also noticed, equal in length to
one-fourth of the moon's apparent diameter. The following mornings being
again cloudy, no further observations could be obtained. This cometary
mass will be in close proximity to the earth about the last of November,
1892. Another brilliant meteoric shower may therefore be expected at
that epoch.

  [27] The radiant of the Biela meteors is near _Gamma Andromedae_.


The Meteors of April 20.

Meteoric showers have occurred about the 20th of April in the following
years:

  B.C.  687
         15
  A.D.  582
       1093 }
       1094 }
       1095 }
       1096 }
       1122    }
       1123    }
       1803

The probability that these meteors are derived from a ring which
intersects the earth's orbit, was first suggested by Arago in 1836. A
comparison of dates led Herrick to designate 27 years as the probable
period of the cluster. In the _Astronomische Nachrichten_, No. 1632, Dr.
Weiss called attention to the fact that the orbit of the first comet of
1861 very nearly intersects that of the earth, in longitude 210 deg.--the
point passed by the latter at the epoch of the April meteoric shower. A
relation between the meteors and the comet, indicating an approximate
equality of periods, was thus suggested as probable. But the comet,
according to Oppolzer, does not complete a revolution in less than 415
years. If, therefore, the meteoric period is nearly the same, the known
dates of star-showers indicate a diffusion of meteoroids around one half
of the orbit previous to the display of the year 15 B.C. No subsequent
perturbation, then, of a particular _part_ could sensibly effect the
general orbit of the stream. The infrequency of the display renders,
therefore, the hypothesis of a long period extremely improbable.

The entire interval between 687 B.C. and A.D. 1803 is 2490 years, or 92
periods of 27.0652 years; and the known dates are all satisfied by the
following scheme:

  B.C.  687 to B.C.   15 .. 672 years = 25 periods of 26.8800 _y._ each.
         15 to A.D.  582 .. 597   "   = 22   "        27.1363       "
  A.D.  582 to      1095 .. 513   "   = 19   "        27.0000       "
       1095 to      1122 ..  27   "   =  1   "        27.0000       "
       1122 to      1803 .. 681   "   = 25   "        27.2400       "

With a period of 27 years, the perihelion being interior to the earth's
orbit, the aphelion distance of the meteors would be very nearly equal
to the distance of Uranus. The next shower, if the assumed period be
correct, ought to occur about 1884. It is worthy of remark that near the
time of the last (hypothetical) return Mr. Du Chaillu witnessed the
meteors of this epoch, in considerable numbers, in the interior of
Africa.


The Meteors of December 12.

Meteoric showers have occurred about the 12th of December in the
following years:

1. A.D. 901. "The whole hemisphere was filled with those meteors called
falling-stars from midnight till morning, to the great surprise of the
beholders in Egypt."

2. In 930 a remarkable shower of falling stars was observed in China.

3. Extraordinary meteoric phenomena were observed at Zurich at the same
epoch in 1571.

4. On the night of the 11th and 12th of December, 1833, a great number
of shooting-stars were seen at Parma. At the maximum as many as ten
were visible at the same time.

5. (Doubtful.) 1861, 1862, and 1863. Maximum probably in 1862. The
meteors at this return were far from being comparable in numbers with
the ancient displays. The shower, however, was distinctly observed.
R. P. Greg, Esq., of Manchester, England, says the period of December
12, 1862, was "exceedingly well defined."

These dates indicate a period of about 29-1/8 years. Thus:

   901 to  930       1 period  of 29.000 years.
   930 to 1571      22 periods of 29.136   "
  1571 to 1833       9 periods of 29.111   "
  1833 to 1862       1 period  of 29.000   "


Meteors of October 16-20.

Meteoric showers were observed from the 16th to the 20th of October in
the years 288, 1436, 1439, 1743, and 1798. These dates render it
somewhat probable that the period is about 27-1/2 years. Thus:

  A.D.  288 to 1439     42 periods of 27.405 years each.
       1439 to 1743     11    "       27.636   "     "
       1743 to 1798      2    "       27.500   "     "

If these periods are correct, it is a remarkable coincidence that the
aphelion distances of the meteoric rings of April 20, October 18,
November 14, and December 12, as well as those of the comets 1866 I.,
and 1867 I., are all nearly equal to the mean distance of Uranus.


The Meteors of April 30, May 1.

Professor Schiaparelli, in his list of meteoric showers whose radiant
points are derived from observations made in Italy during the years
1868, 1869, and 1870, describes one as occurring on April 30 and May 1;
the radiant being in the Northern Crown. The same shower has also been
recognized by R. P. Greg, F.R.S., of Manchester, England. This
meteor-stream, it is now proposed to show, is probably derived from one
much more conspicuous in ancient times.

In Quetelet's "Physique du Globe" we find meteoric displays of the
following dates. In each case the corresponding day for 1870 is also
given,[28] in order to exhibit the close agreement of the epochs:

  1. A.D. 401, April 9th; corresponding to April 29th, for 1870.
  2.      538,   "   6th;       "          April 25th,      "
  3.      839,   "  17th;       "          May    1st,      "
  4.      927,   "  17th;       "          April 30th,      "
  5.      934,   "  18th;       "          May    1st,      "
  6.     1009,   "  16th;       "          April 28th,      "

  [28] Making proper allowance for the precession of the equinoxes.

The epochs of 927 and 934 suggest as probable the short period of 7
years. It is found accordingly that the entire interval of 608
years--from 401 to 1009--is equal to 89 mean periods of 6.8315 years
each. With this approximate value the six dates are all represented as
follows:

  From A.D. 401 to A.D. 538,   20 periods of 6.85 years.
            538 to      839,   44   "        6.84   "
            839 to      927,   13   "        6.77   "
            927 to      934,    1   "        7.00   "
            934 to     1009,   11   "        6.82   "

This period nearly corresponds to those of several comets whose aphelion
distances are somewhat greater than the mean distance of Jupiter. So
long as the cluster occupied but a small arc of the orbit the displays
would evidently be separated by considerable intervals. The comparative
paucity of meteors in modern times may be explained by the fact that the
ring has been subject to frequent perturbations by Jupiter.


Groups in which the Meteoroids are sparsely scattered.

By the labors of Heis, Greg, Herschel, Schiaparelli, and others, the
radiants of more than fifty sparsely strewn meteor-systems have been
determined. Of these the following, which are well defined, seem worthy
of special study:

  DATE.            POSITION OF RADIANT.
                     R. A.      N. Decl.
  January 1-4         234 deg.        51 deg.
  January 18          232 deg.        36 deg.
  April 25            142 deg.        53 deg.

The orbits and periods, except in the few cases previously considered,
are entirely unknown. Some of the observed clusters are probably the
_debris_ of ancient comets whose aphelia were in the vicinity of
Jupiter's orbit.




CHAPTER X.

THE ORIGIN OF COMETS AND METEORS.


The fact that comets and meteors, or at least a large proportion of such
bodies, have entered the solar system from stellar space, is now
admitted by all astronomers. The question, however, in regard to the
origin and nature of these cosmical clouds still remains undecided. The
theory that they consist of matter expelled with great velocity from the
fixed stars appears to harmonize the greatest number of facts, and is
accordingly entitled to respectful consideration. The evidence by which
it is sustained may be briefly stated as follows:

1. The observations of Zollner, Respighi, and others, have indicated the
operation of stupendous eruptive forces beneath the solar surface. The
rose- prominences, which Janssen and Lockyer have shown to be
masses of incandescent hydrogen, are regarded by Professor Respighi as
phenomena of eruption. "They are the seat of movements of which no
terrestrial phenomenon can afford any idea; masses of matter, the volume
of which is many hundred times greater than that of the earth,
completely changing their position and form in the space of a few
minutes." The nature of this eruptive force is not understood. We may
assume, however, that it was in active operation long before the sun
had contracted to its present dimensions.

2. With an initial velocity of projection equal to 380 miles per second,
the matter thrown off from the sun would be carried beyond the limits of
the solar system, never to return. With velocities somewhat less, it
would be transported to distances corresponding to those of the aphelia
of the periodic comets.

3. On the 7th of September, 1871, Professor Young, of Dartmouth
College,[29] witnessed an extraordinary explosion on the sun's surface.
The observer, with his telescope, followed the expelled matter to an
elevation of over 200,000 miles. The mean velocity between the altitudes
of 100,000 and 200,000 miles was 166 miles per second. This rate of
motion _in vacuo_ would indicate an initial velocity of about 260 miles
per second. But the sun is surrounded by an extensive atmosphere, whose
resistance must have greatly retarded the velocity of the outrush before
reaching the height of 100,000 miles. The original velocity of these
hydrogen clouds was therefore sufficient, in all probability, to have
carried them, if unresisted, beyond the solar domain. Solid or dense
matter propelled with equal force would doubtless have been driven off
never to return.[30]

  [29] Boston Journal of Chemistry, November, 1871.

  [30] See Mr. Proctor's interesting discussion of this subject in
       the Monthly Notices of the R.A.S., vol. xxxii.

4. This eruptive force, whatever be its nature, is probably common to
the sun and the so-called fixed stars. If so, the dispersed fragments
of ejected matter ought to be found in the spaces intervening between
sidereal systems. Accordingly, the phenomena of comets and meteors have
demonstrated the existence of such matter, widely diffused, in the
portions of space through which the solar system is moving.

5. According to Mr. Sorby the microscopic structure of the aerolites he
has examined points evidently to the fact that they have been at one
time in a state of fusion from intense heat,--a fact in striking harmony
with this theory of their origin.

6. The velocity with which some meteoric bodies have entered the
atmosphere has been greater than that which would have been acquired by
simply falling toward the sun from any distance, however great. On the
theory of their sidereal origin, this excess of velocity has been
dependent on the primitive force of expulsion. The shower of aerolites
which fell at Pultusk, Poland, on the 30th of January, 1868,[31] is not
only a remarkable illustration of the fact here stated, but also of
another which may be accounted for by the same theory, viz.: that
meteoric bodies sometimes enter the solar system in groups or clusters.

  [31] See Chapter VII.

7. A striking argument in favor of this theory may be derived from the
researches of the late Professor Graham, considered in connection with
those of Dr. Huggins and other eminent spectroscopists. Professor Graham
found large quantities of hydrogen confined in the pores or cavities of
certain meteoric masses. Now, the spectroscope has shown that the sun's
rose- prominences consist of immense volumes of incandescent
hydrogen; that the same element exists in great abundance in many of the
fixed stars, and even in certain nebulae; and that the star in the
Northern Crown, whose sudden outburst in 1866 so astonished the
scientific world, afforded decided indications of its presence.


THE END.




_BY THE AUTHOR OF THIS VOLUME._


  METEORIC ASTRONOMY:
  A TREATISE ON
  SHOOTING STARS, FIRE BALLS,
  AND AEROLITES.

  BY DANIEL KIRKWOOD, LL.D.

  12mo. Extra Cloth. $1.50.


  For sale by Booksellers generally, or will be sent by mail,
  postpaid, on receipt of the price by

  J. B. LIPPINCOTT & CO., Publishers,
  _715 and 717 Market St., Philadelphia_.




Transcriber's Note: Obvious errors in spelling and punctuation have been
corrected. Footnotes have been renumbered and moved from the page end to
the end of the paragraph. Images have been moved from the
middle of a paragraph to the closest paragraph break.






End of the Project Gutenberg EBook of Comets and Meteors, by Daniel Kirkwood

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