Remarks on the foregoing Table.

1. The first two members of the group, Flora and Ariadne, have very nearly the same mean distance. Immediately exterior to these, however, occurs a wide interval, including the distance at which seven periods of an asteroid would be equal to two of Jupiter.

2. On the outer limit of the ring Freia, Cybele, and Sylvia have also nearly equal distances, and are separated from the next interior member by a wide space including the distance at which two periods would be equal to one of Jupiter, and also that at which five would be equal to one of Saturn.

3. Besides these extreme members of the group, our table contains eighty-six minor planets, all of which are included between the distances 2·26 and 3·16; the mean interval between them being 0·0105. The distances are distributed as follows:

2·26 to 2·366 minimum.
2·36 to 2·4619 maximum.
2·46 to 2·564 minimum.
2·56 to 2·6616}maximum.
2·66 to 2·7616
2·76 to 2·868
2·86 to 2·964}minimum.
2·96 to 3·063
3·06 to 3·1610 maximum.

The clustering tendency is here quite apparent.

4. The three widest intervals between these bodies are—

(a) between Leucothea and Pales0·0785,
(b) between Leto and Terpsichore0·0755,
(c) between Thetis and Hestia0·0525;

and these, it will be observed, are the three remaining distances, indicated on a previous page, at which the periods of the primitive meteoric asteroids would be commensurable with that of Jupiter. Now, if the original ring consisted of an indefinite number of separate particles moving with different velocities, according to their respective distances, those revolving at the distance 2·4935—in the interval between Thetis and Hestia—would make precisely three revolutions while Jupiter completes one. A planetary particle at this distance would therefore always come in conjunction with Jupiter in the same parts of its path: consequently its orbit would become more and more eccentric until the particle itself would unite with others, either exterior or interior, thus forming an asteroidal nucleus, while the primitive orbit of the particle would be left destitute of matter, like the interval in Saturn's ring.

5. If the distribution of matter in the zone was originally nearly continuous, as in the case of Saturn's rings, it would probably break up into a number of concentric annuli. On account, however, of the great perturbations to which they were subject, these narrow rings would frequently come in collision. After their rupture, and while the fragments were collecting in the form of asteroids, numerous intersections of orbits and new combinations of matter would occur, so as to leave, in the present orbits, but few traces of the rings from which the existing asteroids were derived. A comparison, however, of the elements of Clytie and Frigga shows a striking similarity; and Professor Lespiault has pointed out a corresponding likeness between the orbits of Fides and Maia. For these four asteroids the nodal lines and also the inclinations are nearly the same; while the periods differ by only a few days. It is probable, therefore, that they are all fragments of the same narrow ring. Finally, as they all move nearly in the same plane, they must at some future time approach extremely near each other, and perhaps become united in one large asteroid.

[CHAPTER XIV.]
ORIGIN OF METEORS—THE NEBULAR HYPOTHESIS.

In regard to the physical history of those meteoric masses which, in such infinite numbers, traverse the interplanetary spaces, our knowledge is exceedingly limited. Such as have reached the earth's surface consist of various elements in a state of combination. It has been remarked, however, by a distinguished scientist[32] that "the character of the constituent particles of meteorites, and their general microscopical structure, differ so much from what is seen in terrestrial volcanic rocks, that it appears extremely improbable that they were ever portions of the moon, or of a planet, which differed from a large meteorite in having been the seat of a more or less modified volcanic action." As the celebrated nebular hypothesis seems to afford a very probable explanation of the origin of those bodies, whether in the form of rings or sporadic masses, its brief consideration may not be destitute of interest. We will merely premise that the existence of true nebulæ in the heavens—that is, of matter consisting of luminous gas—has been placed beyond doubt by the revelations of the spectroscope.

As a group, our solar system is comparatively isolated in space; the distance of the nearest fixed star being at least seven thousand times that of Neptune, the most remote known planet. Besides the central or controlling orb, it contains, so far as known at present, ninety-nine primary planets, eighteen satellites, three planetary rings, and nearly eight hundred comets. In taking the most cursory view of this system we cannot fail to notice the following interesting facts in regard to the motions of its various members:

1. The sun rotates on his axis from west to east.

2. The primary planets all move nearly in the plane of the sun's equator.

3. The orbital motions of all the planets, primary and secondary, except the satellites of Uranus and Neptune, are in the same direction with the sun's rotation.

4. The direction of the rotary motions of all the planets, primary and secondary, in so far as has been observed, is identical with that of their orbital revolutions; viz., from west to east.

5. The rings of Saturn revolve about the planet in the same direction.

6. The planetary orbits are all nearly circular.

7. The cometary is distinguished from the planetary portion of the system by several striking characteristics: the orbits of comets are very eccentric and inclined to each other, and to the ecliptic at all possible angles. The motions of a large proportion of comets are from east to west. The physical constitution of the latter class of bodies is also very different from that of the former; the matter of which comets are composed being so exceedingly attenuated, at least in some instances, that fixed stars have been distinctly visible through what appeared to be the densest portion of their substance.

None of these facts are accounted for by the law of gravitation. The sun's attraction can have no influence whatever in determining either the direction of a planet's motion, or the eccentricity of its orbit. In other words, this power would sustain a planetary body moving from east to west, as well as from west to east; in an orbit having any possible degree of inclination to the plane of the sun's equator, no less than in one coincident with it; or, in a very eccentric ellipse, as well as in one differing but little from a circle. The consideration of the coincidences which we have enumerated led Laplace to conclude that their explanation must be referred to the mode of our system's formation—a conclusion which he regarded as strongly confirmed by the contemporary researches of Sir William Herschel. Of the numerous nebulæ discovered and described by that eminent observer, a large proportion could not, even by his powerful telescope, be resolved into stars. In regard to many of these, it was not doubted that glasses of superior power would show them to be extremely remote sidereal clusters. On the other hand, a considerable number were examined which gave no indications of resolvability. These were supposed to consist of self-luminous, nebulous matter—the chaotic elements of future stars. The great number of these irresolvable nebulæ scattered over the heavens and apparently indicating the various stages of central condensation, very naturally suggested the idea that the solar system, and perhaps every other system in the universe, originally existed in a similar state. The sun was supposed by Laplace to have been an exceedingly diffused, rotating nebula, of spherical or spheroidal form, extending beyond the orbit of the most distant planet; the planets as yet having no separate existence. This immense sphere of vapor, in consequence of the radiation of heat and the continual action of gravity, became gradually more dense, which condensation was necessarily attended by an increased angular velocity of rotation. At length a point was thus reached where the centrifugal force of the equatorial parts was equal to the central attraction. The condensation of the interior meanwhile continuing, the equatorial zone was detached, but necessarily continued to revolve around the central mass with the same velocity that it had at the epoch of its separation. If perfectly uniform throughout its entire circumference, which would be highly improbable, it would continue its motion in an unbroken ring, like that of Saturn; if not, it would probably collect into several masses, having orbits nearly identical. "These masses should assume a spheroidal form, with a rotary motion in the direction of that of their revolution, because their inferior articles have a less real velocity than the superior; they have therefore constituted so many planets in a state of vapor. But if one of them was sufficiently powerful to unite successively by its attraction all the others about its center, the ring of vapors would be changed into one spheroidal mass, circulating about the sun, with a motion of rotation in the same direction with that of revolution."[33] Such, according to the theory of Laplace, is the history of the formation of the most remote planet of our system. That of every other, both primary and secondary, would be precisely similar.

In support of the nebular hypothesis, of which the foregoing is a brief general statement, we remark that it furnishes a very simple explanation of the motions and arrangements of the planetary system. In the first place, it is evident that the separation of a ring would take place at the equator of the revolving mass, where of course the centrifugal force would be greatest. These concentric rings—and consequently the resulting planets—would all revolve in nearly the same plane. It is evident also that the central body must have a revolution on its axis in the same direction with the progressive motion of the planets. Again: at the breaking up of a ring, the particles of nebulous matter more distant from the sun would have a greater absolute velocity than those nearer to it, which would produce the observed unity of direction in the rotary and orbital revolutions. The motions of the satellites are explained in like manner. The hypothesis, moreover, accounts satisfactorily for the fact that the orbits of the planets are all nearly circular. And finally, it presents an obvious explanation of the rings of Saturn. It would almost seem, indeed, as if these wonderful annuli had been left by the Architect of Nature, as an index to the creative process.

The argument derived from the motions of the various members of the solar system is not new, having been forcibly stated by Laplace, Pontécoulant, Nichol, and other astronomers. Its full weight and importance, however, have not, we think, been duly appreciated. That a common physical cause has determined these motions, must be admitted by every philosophic mind. But apart from the nebular hypothesis, no such cause, adequate both in mode and measure, has ever been suggested;—indeed none, it seems to us, is conceivable. The phenomena which we have enumerated demand an explanation, and this demand is met by the nebular hypothesis. It will be found, therefore, when closely examined, that the evidence afforded by the celestial motions is sufficient to give the theory of Laplace a very high degree of probability.

A comparison of the facts known in regard to comets, falling-stars, and meteoric stones, seems to warrant the inference that they are bodies of the same nature, and perhaps of similar origin; differing from each other mainly in the accidents of magnitude and density. The hypothesis of Laplace very obviously accounts for the formation of planets and satellites, moving in the same direction, and in orbits nearly circular; but how, it may be asked, can the same theory explain the extremely eccentric, and in some cases retrograde, motions of comets and aerolites? This is the question to which we now direct our attention.

After the nuclei of the solar and sidereal systems had been established in the primitive nebula, and when, in consequence, immense gaseous spheroids had collected around such nuclei, we may suppose that about the points of equal attraction between the sun and neighboring systems, portions of nebulous matter would be left in equilibrio. Such outstanding nebulosities would gradually contract through the operation of gravity; and if, as would sometimes be the case, the solar attraction should preponderate, they would commence falling toward our system. Unless disturbed by the planets they would probably move round the sun in parabolas. Should they pass, however, near any of the large bodies of the system, their orbits might be changed into ellipses by planetary perturbation. Such was the view of Laplace in regard to the origin of comets.

It seems probable, however, that many of these bodies originated within the solar system, and belong properly to it. The outer rings thrown off by the planets may have been at too great distances from the primaries to form stable satellites. Such masses would be separated by perturbation from their respective primaries, and would revolve round the sun in independent orbits. Again: small portions of nebulous matter may have been abandoned as primary rings, at various intervals between the planetary orbits. At particular distances such rings would be liable to extraordinary perturbations, in consequence of which their orbits would ultimately assume an extremely elliptical form, like those of comets, and perhaps also those of meteors. It was shown in Chapter XIII. that several such regions occur in the asteroid zone between Mars and Jupiter. We may add, in confirmation of this view, that there are twelve known comets whose periods are included between those of Flora and Jupiter. Their motions are all direct; their orbits are less eccentric than those of other comets; and the mean of their inclinations is about the same as that of the asteroids. These facts certainly appear to indicate some original connection between these bodies and the zone of minor planets.

The nebular hypothesis, it is thus seen, accounts satisfactorily for the origin of comets, aerolites, fire-balls, shooting-stars, and meteoric rings; regarding them all as bodies of the same nature, moving in cometary orbits about the sun. In this theory, the zodiacal light is an immense swarm of meteor-asteroids; so that the meteoric theory of solar heat, explained in a previous chapter, finds its place as a part of the same hypothesis.

[CONCLUSION.]

Some of the prominent results of observation and research in meteoric astronomy may be summed up as follows:

1. The shooting-stars of November, August, and other less noted epochs, are derived from elliptic rings of meteoric matter which intersect the earth's orbit.

2. Meteoric stones and the matter of shooting-stars coexist in the same rings; the former being merely collections or aggregations of the latter.

3. The most probable period of the November meteors is thirty-three years and three months. Leverrier's elements of this ring agree so closely with Oppolzer's elements of the comet of 1866 as to render it probable that the latter is merely a large meteor belonging to the same annulus.

4. The spectroscopic examination of this comet (of 1866) by William Huggins, F.R.S., indicated that the nucleus was self-luminous, that the coma was rendered visible by reflecting solar light, and that "the material of the comet was similar to the matter of which the gaseous nebulæ consist."

5. The time of revolution of the August meteors is believed to be about 105 years. M. Schiaparelli has found a striking similarity between the elements of this ring and those of the third comet of 1862. The same distinguished astronomer has shown, moreover, that a nebulous mass of considerable extent, drawn into the solar system ab extra, would form a ring or stream.

6. The aerolitic epochs, established with more or less certainty, are the following:

1. February 15th–19th.
2. March 12th–15th.
3. April 10th–12th.
4. April 18th–26th.
5. May 8th–14th; or especially, 12th–13th.
6. May 19th.
7. July 13th–14th.
8. July 26th.
9. August 7th–11th.
10. October 13th–14th.
11. November 11th–14th.
12. November 27th–30th.
13. December 7th–13th.

About one-half of this number are also known as shooting-star epochs.

7. The epoch of November 27th–30th corresponds with that of the earth's crossing the orbit of Biela's two comets. The aerolites of this epoch may therefore have been moving in nearly the same path.

8. A greater number of aerolitic falls are observed—

1. By day than by night.
2. In the afternoon than in the forenoon.
3. When the earth is in aphelion than when in perihelion.

The first fact is accounted for by the difference in the number of observers; the second indicates that a majority of aerolites have direct motion; and the third is dependent on the relative lengths of the day and night in the aphelic and perihelic portions of the orbit.

9. The observed velocities of meteorites are incompatible with the theory of their lunar origin.

10. If the meteoric swarm of November 14th has a period of thirty-three years, Biela's comet passed very near, if not actually through it toward the close of 1845, about the time of the comet's separation. Was the division of the cometary mass produced by the encounter?

11. The rings of Saturn may be regarded as dense meteoric masses, and the principal or permanent division accounted for by the disturbing influence of the interior satellites.

12. The asteroidal space between Mars and Jupiter is probably a wide meteoric ring in which the largest aggregations are visible as minor planets. In the distribution of the mean distances of the known members of the group a clustering tendency is quite obvious.

13. The meteoric masses encountered by Encke's comet may account for the shortening of the period of the latter without the hypothesis of an ethereal medium.

[APPENDIX.]

A.
The Meteors of November 14th.

The American Journal of Science and Arts for May, 1867 (received by the author after the first chapters of this work had gone to press), contains an interesting article by Professor Newton "On certain recent contributions to Astro-Meteorology." Of the five possible periods of the November ring, first designated by Professor N, it is now granted that the longest, viz., 33¼ years, is most probably the true one. The results of Leverrier's researches in regard to the epoch at which this meteoric mass was introduced into the solar system, are given in the same article. This distinguished astronomer supposes the group of meteors to have been thrown into an elliptic orbit by the disturbing influence of Uranus. The meteoric stream, according to the most trustworthy elements of its orbit, passed extremely near that planet about the year 126 of our era; which date is therefore assigned by Leverrier as the probable time of its entrance into the planetary system. This result, however, requires confirmation.

Although the earliest display of the November meteors, so far as certainly known, was that of the year 902, several more ancient exhibitions may, with some probability, be referred to the same epoch. These are the phenomena of 532, 599, and 600, A.D., and 1768, B.C. (See Quetelet's Catalogue.) The time of the year at which these showers occurred is not given. The years, however, correspond very well with the epochs of the maximum display of the November meteors. The intervals arranged in consecutive order, are as follows:

From B.C. 1768 to A.D. 532,69 periods of 33·319 years each.
"A.D.532to"599·5,2"33·750"
""599·5to"902,9"33·614"
""902to"934,1"32·000"
""934to"1002,2"34·000"
""1002to"1101,3"33·000"
""1101to"1202,3"33·667"
""1202to"1366,5"32·800"
""1366to"1533,5"33·400"
""1533to"1698,5"33·000"
""1698to"1799,3"33·667"
""1799to"1833,1"34·000"
""1833to"1866,1"33·000"

The first three dates are alone doubtful. The whole number of intervals from B.C. 1768 to A.D. 1866 is 109, and the mean length is 33·33 years.

The perturbations of the ring by Jupiter, Saturn, and Uranus, are doubtless considerable. It is worthy of note that—

14periods ofJupiterare nearly equal to5of the ring.
9"Saturn""8"
23"Uranus""58"

This group or stream has its perihelion at the orbit of the earth; its aphelion, at that of Uranus. (See diagram, p. 24.) It must therefore produce star-showers at the latter as well as at the former. Our planet, moreover, at each encounter appropriates a portion of the meteoric matter; while at the remote apsis of the stream Uranus in all probability does the same. The matter of the ring will thus by slow degrees be gathered up by the two planets.

B.
Comets and Meteors.

The recent researches and speculations of European astronomers in regard to the origin of comets and of meteoric streams, have suggested to the author the propriety of reproducing the following extracts from an article written by himself, in July, 1861, and published in the Danville Quarterly Review for December of that year:

"Different views are entertained by astronomers in regard to the origin of comets; some believing them to enter the solar system ab extra; others supposing them to have originated within its limits. The former is the hypothesis of Laplace, and is regarded with favor by many eminent astronomers. It seems to afford a plausible explanation of the paucity of large comets during certain long intervals of time. In one hundred and fifty years, from 1600 to 1750, sixteen comets were visible to the naked eye; of which eight appeared in the twenty-five years from 1664 to 1689. Again, during sixty years from 1750 to 1810, only five comets were visible to the naked eye, while in the next fifty years there were double that number. Now, according to Laplace's hypothesis, patches of nebulous matter have been left nearly in equilibrium in the interstellar spaces. As the sun, in his progressive motion, approaches such clusters, they must, by virtue of his attraction, move toward the center of our system; the nearer portions with greater velocity than the more remote. The nebulous fragments thus introduced into our system would constitute comets; 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. On the other hand, the passage of the system through a region of space destitute of this chaotic vapor would be followed by a corresponding paucity of comets.

"Before the invention of the telescope, the appearance of a comet was a comparatively rare occurrence. The whole number visible to the naked eye during the last three hundred and sixty years has been fifty-five; or a mean of fifteen per century. The recent rate of telescopic discovery, however, has been about four or five annually. As many of these are extremely faint, it seems probable that an indefinite number, too small for detection, may be constantly traversing the solar domain. If we adopt Laplace's hypothesis of the origin of comets, we may suppose an almost continuous fall of primitive nebular matter toward the center of the system—the drops of which, penetrating the earth's atmosphere, produce sporadic meteors; the larger aggregations forming comets. The disturbing influence of the planets may have transformed the original orbits of many of the former, as well as of the latter, into ellipses. It is an interesting fact that the motions of some luminous meteors—or cometoids, as perhaps they might be called—have been decidedly indicative of an origin beyond the limits of the planetary system.

"But how are the phenomena of periodic meteors to be accounted for, in accordance with this theory?

"The division of Biela's comet into two distinct parts suggests several interesting questions in cometary physics. The nature of the separating force remains to be discovered; 'but it is impossible to doubt that it arose from the divellent action of the sun, whatever may have been the mode of operation.'

"'A signal manifestation of the influence of the sun,' says a distinguished writer, 'is sometimes afforded by the breaking up of a comet into two or more separate parts, on the occasion of its approach to the perihelion. Seneca relates that Ephoras, an ancient Greek author, makes mention of a comet which before vanishing was seen to divide itself into two distinct bodies. The Roman philosopher appears to doubt the possibility of such a fact; but Keppler, with characteristic sagacity, has remarked that its actual occurrence was exceedingly probable. The latter astronomer further remarked that there were some grounds for supposing that two comets, which appeared in the same region of the heavens in the year 1618, were the fragments of a comet that had experienced a similar dissolution. Hevelius states that Cysatus perceived in the head of the great comet of 1618 unequivocal symptoms of a breaking up of the body into distinct fragments. The comet when first seen in the month of November, appeared like a round mass of concentrated light. On the 8th of December it seemed to be divided into several parts. On the 20th of the same month it resembled a multitude of small stars. Hevelius states that he himself witnessed a similar appearance in the head of the comet of 1661.'[34] Edward Biot, moreover, in his researches among the Chinese records, found an account of 'three dome-formed comets' that were visible simultaneously in 896, and pursued very nearly the same apparent path.

"Another instance of a similar phenomenon is recorded by Dion Cassius, who states that a comet which appeared eleven years before our era, separated itself into several small comets.

"These various examples are presented at one view, as follows:

"I. Ancient bipartition of a comet.—Seneca, Quæst. Nat., lib. VII. cap. XVI.

"II. Separation of a comet into a number of fragments, 11 B.C.—Dion Cassius.

"III. Three comets seen simultaneously pursuing the same orbit, A.D. 896—Chinese records—Comptes Rendus, tom. xx. 1845, p. 334.

"IV. Probable separation of a comet into parts, A.D. 1618.—Hevelius, Cometographia, p. 341.—Keppler, De Cometis, p. 50.

"V. Indications of separation, 1661.—Hevelius, Cometographia, p. 417.

"VI. Bipartition of Biela's comet, 1845–6.

"In view of these facts it seems highly probable, if not absolutely certain, that the process of division has taken place in several instances besides that of Biela's comet. May not the force, whatever it is, that has produced one separation, again divide the parts? And may not this action continue until the fragments become invisible? According to the theory now generally received, the periodic phenomena of shooting-stars are produced by the intersections of the orbits of such nebulous bodies with the earth's annual path. Now there is reason to believe that these meteoric rings are very elliptical, and in this respect wholly dissimilar to the rings of primitive vapor which, according to the nebular hypothesis, were successively abandoned at the solar equator; in other words, that the matter of which they are composed moves in cometary rather than planetary orbits. May not our periodic meteors be the debris of ancient but now disintegrated comets, whose matter has become distributed around their orbits?"

C.
Biela's Comet and the Meteors of November 27th–30th.

At the close of Chapter IV. it was suggested that the meteors of November 27th–30th might possibly be derived from a ring of meteoric matter moving in the orbit of Biela's comet. Since that chapter was written similar conjectures have been started in the Astronomische Nachrichten[35] by Dr. Edmund Weiss and Prof. d'Arrest. The latter attempts to show that the December meteors may be derived from the same ring. The question will doubtless be decided at no distant day.

D.
The First Comet of 1861 and the Meteors of April 20th.

Recent investigations render it probable that the orbit of the first comet of 1861 is identical with that of the meteors of April 20th. The orbit is nearly perpendicular to the ecliptic.

[FOOTNOTES]

[1] For a full description, see Silliman's Journal for January and April, 1834 (Prof. Olmsted's article). Also a valuable paper, in the July No. of the same year, by Prof. Twining.

[2] Physique du Globe, Chap. IV.

[3] Professor Olmsted estimated the number of meteors, visible at New Haven, during the night of November 12th–13th, 1833, at 240,000.

[4] Conde says, "there were seen, as it were lances, an infinite number of stars, which scattered themselves like rain to the right and left, and that year was called 'the year of stars.'"

[5] In 1202, "on the last day of Muharrem, 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."—Quoted by Prof. Newton, in Silliman's Journal, May, 1864.

[6] Am. Journ. of Sci. and Arts, May and July, 1864.

[7] The stream or arc of meteors is several years in passing its node. The first indication of the approach of the display of 1866 was the appearance of meteors in unusual numbers at Malta, on the 13th of November, 1864. The great length of the arc is indicated, moreover, by the showers of 931 and 934.

[8] Silliman's Journ. for Sept. and Nov., 1861.

[9] The numerical results here given are those found by Professor Newton. See Silliman's Journ. for March, 1865.

[10] The diameters of the asteroids are derived from a table by Prof. Lespiault, in the Rep. of the Smithsonian Inst. for 1861, p. 216.

[11] "It appears probable, from the researches of Schreibers, that 700 fall annually."—Cosmos, vol. i. p. 119 (Bohn's Ed.). Reichenbach makes the number much greater.

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

[13] Cosmos, vol. i. p. 120.

[14] Leverrier's Annals of the Observatory of Paris, vol. i. p. 38.

[15] "This is a remarkable example of a stone arriving on the earth with a temperature approaching that of the interplanetary spaces. Aerolites containing much iron, a substance which conducts heat well, get thoroughly heated by their passage through the atmosphere. But the stony aerolites, containing less iron, conducting heat badly, preserve in their interior the temperature of the locality from which they fall; their surface only is heated, and generally fused. When the stones are large, the excessive cold of their interior portion, which must be nearly that of interplanetary space, is remarked; but when small, they remain hot for some time."—Dr. Phipson.

[16] Silliman's Journal, September, 1864.

[17] The same explanation is given by T. M. Hall, F.G.S., in the Popular Science Review for Oct. 1866.

[18] This list contains nothing but aerolites. In the Edinburgh Review for January, 1867, we find the following statements: "Out of the large number of authentic aerolites preserved in mineralogical collections, two only—one on the 10th of August, and one on the 13th of November—are recorded to have fallen on star-shower dates. On the other hand, five or six meteorites, on the epoch of the 13th–14th of October, belong to a date when star-showers, so far as is at present known, do not make their appearance." The inaccuracy of the former statement is sufficiently apparent. In regard to the latter we remark that Quetelet's Catalogue gives one star-shower on the 14th of October, and another on the 12th.

[19] The date of this remarkable occurrence is worthy of note as a probable aerolite epoch. From the 12th to the 15th of March we have the following falls of meteoric stones:

Numerous fire-balls have appeared at the same epoch.

[20] The innermost or semi-transparent ring of Saturn appears to be similarly constituted, as the body of the planet is seen through it without any distortion whatever.

[21] Origin of the Stars, p. 173.

[22] Origin of the Stars, p. 184.

[23] Since the above was written Prof. Ennis has informed the author that, without making any estimate of his own, he adopted the density of Jupiter's first satellite as given in Lardner's Handbook of Astronomy.

[24] Origin of the Stars, p. 77.

[25] Youman's Correlation and Conservation of Forces, p. 244.

[26] Iowa Instructor and School Journal for November, 1866, p. 49.

[27] A recent hypothesis in regard to the temporary star of 1572 has been proposed by Alexander Wilcocks, M.D., of Philadelphia. See Journ. Acad. Nat. Sci. of Phila. for 1859.

[28] Gautier's Notice of Recent Researches relating to Nebulæ.—Silliman's Journal for Jan. 1863, and March, 1864.

[29] Outlines of Astronomy, Art. 442.

[30] A learned and highly interesting examination of this hypothesis will be found in a memoir "On the Secular Variations and Mutual Relations of the Orbits of the Asteroids," communicated to the Am. Acad. of Arts and Sciences, April 24th, 1860, by Simon Newcomb, Esq.

[31] For an explanation of the origin of the asteroids according to the nebular hypothesis, see an article by David Trowbridge, A.M., in Silliman's Journal for Nov. 1864, and Jan. 1865.

[32] H. C. Sorby, F.R.S.

[33] Harte's Trans. of Laplace's Syst. of the World, vol. ii., note vii.

[34] Grant's Hist. of Phys. Astr., p. 302.

[35] Nos. 1632 and 1633.

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A Text-book for Schools and Colleges, and a Hand-book for Amateurs and Artists. By G. W. Samson, D.D., President of Columbian College, Washington, D. C. Second Edition. Crown 8vo. Cloth. Price $3.50.

This work comprises a Treatise on the Principles of Man's Nature as addressed by Art, together with a Historic survey of the Methods of Art Execution in the departments of Drawing, Sculpture, Architecture, Painting, Landscape Gardening, and the Decorative Arts. The Round Table says: "The work is incontestably one of great as well as unique value."

HISTORY OF THE U. S. SANITARY COMMISSION.

Being the General Report of its Work on the War of the Rebellion. By Charles J. Stillé, Professor in the University of Pennsylvania. One vol. 8vo. Cloth, beveled boards. Price $3.50.

TERRA MARIÆ; or, Threads of Maryland Colonial History.

By Edward D. Neill, one of the Secretaries of the President of the United States. 12mo. Extra Cloth. Price $2.00.

COMING WONDERS, expected between 1867 and 1875.

By the Rev. M. Baxter, author of "The Coming Battle." One vol. 12mo. Cloth. Price $1.00.

LIPPINCOTT'S PRONOUNCING GAZETTEER OF THE WORLD,

OR GEOGRAPHICAL DICTIONARY.

Revised Edition, with an Appendix containing nearly ten thousand new notices, and the most recent Statistical Information, according to the latest Census Returns, of the United States and Foreign Countries.

Lippincott's Pronouncing Gazetteer gives—

I.—A Descriptive notice of the Countries, Islands, Rivers, Mountains, Cities, Towns, etc., in every part of the Globe, with the most Recent and Authentic Information.

II.—The Names of all Important places, etc., both in their Native and Foreign Languages, with the Pronunciation of the same—a Feature never attempted in any other Work.

III.—The Classical Names of all Ancient Places, so far as they can be accurately ascertained from the best Authorities.

IV.—A Complete Etymological Vocabulary of Geographical Names.

V.—An elaborate Introduction, explanatory of the Principles of Pronunciation of Names in the Danish, Dutch, French, German, Greek, Hungarian, Italian, Norwegian, Polish, Portuguese, Russian, Spanish, Swedish, and Welsh Languages.

Comprised in a volume of over two thousand three hundred imperial octavo pages. Price, $10.00.

From the Hon. Horace Mann, LL.D.,
Late President of Antioch College.

I have had your Pronouncing Gazetteer of the World before me for some weeks. Having long felt the necessity of a work of this kind, I have spent no small amount of time in examining yours. It seems to me so important to have a comprehensive and authentic gazetteer in all our colleges, academies, and schools, that I am induced in this instance to depart from my general rule in regard to giving recommendations. Your work has evidently been prepared with immense labor; and it exhibits proofs from beginning to end that knowledge has presided over its execution. The rising generation will be greatly benefited, both in the accuracy and extent of their information, should your work be kept as a book of reference on the table of every professor and teacher in the country.

[Transcriber's Notes]

Punctuation and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed.

Simple typographical errors were corrected; occasional unbalanced quotation marks retained.

Ambiguous hyphens at the ends of lines were retained.

Text uses both "star shower" and "star-shower"; not changed here.

"Keppler" is spelled that way in this text.