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diff --git a/41606.txt b/41606.txt deleted file mode 100644 index 6ed0989..0000000 --- a/41606.txt +++ /dev/null @@ -1,2912 +0,0 @@ -The Project Gutenberg EBook of Comets and Meteors, by Daniel Kirkwood - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: Comets and Meteors - Their phenomena in all ages; their mutual relations; and - the theory of their origin. - -Author: Daniel Kirkwood - -Release Date: December 11, 2012 [EBook #41606] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK COMETS AND METEORS *** - - - - -Produced by sp1nd and the Online Distributed Proofreading -Team at http://www.pgdp.net (This file was produced from -images generously made available by The Internet Archive) - - - - - - - - - - [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 retard -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 negroes 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 negroes 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 negroes. 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-colored 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-colored 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. 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