applied by Backlund to the computation of the movements of the asteroid Iphigenia. The original method consists in integrating the differential equations of perturbations, according to analytical methods, instead of by mechanical quadratures; Gylden's idea appears to lead to as simple forms of computation as the older methods, but possesses several great advantages, especially in the checks upon the accuracy of the computation at every step of the process. By means of analytical formulæ developed by him some years ago as preliminary to the present work, he is able to express the coordinates as well as the sines and cosines of the co-ordinates of the perturbed bodies in rapidly converging series. Dr. Backlund, in applying Gylden's method to the computation of the special perturbations of Iphigenia, has taken account only of the disturbances introduced by Jupiter during three semi-revolutions of the asteroid. He divides the orbit of the planets into sixteen equiangular portions of twenty-two degrees each, for each of which the perturbations are independ ently computed.-Vierteljahrsschr. Astron. Gesellsch., X., 36.

GALLE'S PATH OF THE METEOR OF JUNE 17, 1873.

The orbit of the bright meteor observed in Austria and Germany on the 17th of June, 1873, has been carefully investigated by Professor Galle. Having satisfied himself that the end of the visible path of the meteor was not far from Zittau, he made a special examination of that region, and gathered many observations which enabled him to fix the actual position of the meteor at the time of its disappearance, and was even able to gather some of those fragments which reached the earth, although their actual fall was not observed by any one, and the connection of the supposed fragments with the original mass is subject to some doubt. In the computation of the orbit, Professor Galle proceeded according to the method elaborated by him as most appropriate to such cases, as follows:

Having determined definitively the exact position of the end of the orbit, each observer's observation then enabled him to determine the apparent plane of motion, the intersection of which planes determined the position of the path followed by the body. Among the thirty-three excellent observations which he was able to use in his study, only

two or three were discordant from the others to such an extent that but little weight could be attributed to them. The linear length of the visible path in the atmosphere was sixty-two geographical miles, the initial point of which was twenty-two miles above the earth's surface, while its end was four and a half miles high. The meteor moved nearly in the plane of the ecliptic, and was approaching the sun at the time that it passed through the earth's atmosphere, cutting the earth's radius vector at an angle of forty-five degrees, the curve of its orbit being that of a hyperbola, and its velocity being somewhat slower than that of the ordinary shootingThe detonation that accompanied this meteor was heard to a distance of forty miles, being most intense in the neighborhood of the end of its path, where at nearly every station it was reported as like the long rolling sound of thunder.-Jahresbericht der Schlesischen Gesellschaft, 1874.

stars.

TWO GROUPS OF NOVEMBER METEORITES.

Professor Kirkwood, of Indiana, communicates to the English journal Nature some remarks on the meteors of November 14, known as the Leonids, because their radiant point is in the constellation of Leo. According to Professor Kirkwood, there are indications of the existence of two distinct and widely separated clusters of meteors moving in orbits very nearly identical, and having therefore very nearly the same radiant point. The principal cluster is that whose appearance at intervals of 33 years was first demonstrated by Professor Newton, while the second group, according to Kirkwood, has a period of 333 years. He suggests that if these two clusters are originally derived from the same meteor cloud, then there must have been a considerable disturbance in their orbits caused by the attraction either of Uranus or of the earth. He cites nine recorded displays of meteors indicating the existence of the second cluster. The first of these occurred in the year 288, and was observed in China on the 28th of September.-—12 A, XII., 85.

ENCKE'S COMET.

Dr. Van Asten, already known by his profound investigations into the movements of Encke's comet, announces that, having lately come into the possession of a number of obser

vations of this object, he hopes to deduce something definite in reference to the peculiarities of its orbit. It is well known that Encke himself believed this comet to be gradually drawing nearer to the sun, in consequence of the resistance offered to its movements by the æther existing throughout space. Van Asten, however, states that his investigations have led him to the surprising result that the observations of 1865 to 1871 can be perfectly accounted for by the general laws of mechanics, quite without calling to our assistance the attractions of unknown bodies or the resistance of an unknown æther. If, under this assumption, we reverse the problem, and attempt to deduce the movements of Jupiter from observations of Encke's comet, we arrive at a result quite identical with that deduced by Bessel, Kruger, and Moller, so that we may be certain that the mean motion of the comet, at the time of its perihelion passage in 1868, experienced not the slightest trace of an acceleration. The assumption that it did experience such an acceleration, even the one-twentieth part of that supposed to exist by Encke, leads to very improbable errors. Van Asten lays stress upon the date, 1868, and says that while at present the comet's motions are fully explicable, yet, if we extend our researches backward, it does seem highly probable that at its perihelion passages in 1858, 1862, and 1865 the comet did successively experience accelerations nearly agreeing with Encke's suppositions. The conclusion, therefore, seems reasonable that the most remarkable feature of this phenomenon is the complete absence of any acceleration at the perihelion passage of 1868; nor can this be explained on the supposition that the disturbing influence of the planet Mercury has been different from that assumed in the calculations. As there can be no doubt that the comet experiences an extraordinary perturbation in the immediate neighborhood of its perihelion, Van Asten explains that he has, for simplicity, made the preliminary assumption that this acceleration took place suddenly at that time; an hypothesis, however, which is not materially different from Encke's assumption that the comet moves in a resisting medium, whose density varies inversely as the square of the distance from the sun; for, if its density vary according to this law, its effect upon the comet would be mainly felt during twenty-five days before and after the perihel

ion. At the appearance of this comet in February, March, and April, 1875, Bredichin, at Moscow, and Struve, at Poulkova, were successful in making observations which are best accounted for by assuming an acceleration since 1871 of about two thirds as much as that indicated at previous apparitions, as though the physical changes in the interior of the comet which occurred in 1868 had affected not only its movements at that time, but also, in a lesser degree, are continued to the present time.

ON COMETARY ORBITS.

In giving a general review of the statistics relative to the orbits of comets, Guillemin states that 177 have parabolic orbits, 73 elliptic, and 14 hyperbolic. To these must be added a large number of other comets not yet accurately computed, so that we may calculate that of these bodies scarcely one sixth are foreign to the solar system, and the remainder circulating about the sun as do the planets. With regard to the inclinations of their orbits to the orbit of the earth, he shows that the greater inclinations are more frequent than the lesser; so that the comets whose paths are confined to the zodiac form scarcely a quarter of those that are known. As regards the direction in which they move in their orbits about the sun, the direct and the retrograde motions are about equally divided. But if we examine in detail the three classes-the parabolic, the elliptic, and the hyperbolic orbits-we find that among the elliptic orbits the direct motions are twice as numerous as the retrograde. As regards the distance to which they approach the sun, 192 have come between the earth and the sun, and 66 between the earth and Jupiter; while between the orbits of Venus and Mars not less than 130 of these have passed. -Bulletin Hebdom. Association Scientifique, 1875, 262.

ON THE STRUCTURE OF COMETS AND METEORS.

From an examination of the gases occluded in the Iowa meteorite of February 12, 1875, Professor Wright, of New Haven, concludes that his results have an important bearing upon the theory of comets and their tails, warranting the following conclusions: First, the stony meteorites are distinguished from the iron ones by having the oxides of

carbon, chiefly the dioxide as their characteristic gases, instead of hydrogen. Second, the proportion of carbon dioxide given off is much greater at low than at high temperatures, and is sufficient to mask the hydrogen in the spectrum. Third, the amount of gases contained in a large meteorite, or cluster of such bodies serving as a cometary nucleus, is sufficient to form the train as ordinarily observed. Fourth, the spectrum of the gases is closely identical with that of several of the comets. We may, then, he states, consider a comet merely as a meteorite of considerable magnitude, or a swarm of many such of lesser size, containing large quantities of carbon dioxide, with some carbonic oxide and hydrogen, and giving off this gas under the influence of solar heat. The gaseous substance in streaming away forms. the train which is visible, partly by reflected sunlight, and partly by its own light, due to some molecular or electrical action which causes it to give the spectrum of the carbon compounds. The loss of the gaseous contents readily explains the loss of the tail and diminution of brightness, observed in the case of several comets in their successive revolutions.--Silliman's Journal, July, 1875, 48.

THE DISTRIBUTION OF COMETARY ORBITS.

Guillemin calls attention in his new work on comets to a feature in the distribution of the orbits of these bodies, which consists especially in the fact that there are special regions of the heavens in which the cometary aphelia are more thickly crowded together than in other regions. Basing his studies upon those of Hoeck, of Utrecht, he places the region within which the least number of cometary aphelia is found in the sector comprised between the ecliptic and a circle inclined thereto at an angle of about 35°, and cutting it in the longitudes 95° and 243°. In explanation of this singularity, Hoeck suggests that if the point toward which the solar system is moving in its great motion of translation occupied the middle of this sector, it would follow that the comets coming from this region would have greater difficulty than any others in following and rejoining the sun. But the direction of the movements of the solar system is such that it does not favor this explanation. Guillemin suggests, therefore, that possibly this sector corresponds to a region