Dr. Bredichin will shortly publish a complete discussion of this interesting subject.-38 G, LXXXVII., 239.

ORBIT OF COMET II., 1840.

This comet was discovered by Galle, of Berlin, January 25, 1840, and was observed until the end of March. Dr. Kowalczyk, of Warsaw, has recently reinvestigated its orbit from a good number of observations, and finds it to be an ellipse, the periodic time being 3789 years. The agree

ment of observation with his theory is very close. Plantamour and Loomis had previously investigated this orbit, and their results may be found in Astronomische Nachrichten, No. 476, and Transactions of the American Academy of Arts and Sciences, vol. viii. Plantamour's orbit was parabolic, and represented the Geneva observations well; Loomis's was an ellipse, which corresponded to a periodic time of 2420 years; Kowalczyk's, however, agrees so well with all the observations that this orbit may be considered as settled. -38 C, LXXXVII., 225; 12 A, March 16, 1876, 386.

ON THE CALCULATION OF THE ABSOLUTE PERTURBATIONS OF COMETS.

Professor H. Gyldèn, Director of the Astronomical Observ. atory at Stockholm, communicates to the Paris Academy of Sciences a method of calculating the absolute perturbations of comets. He states that in all cases where the solution of the problem of these bodies can possibly be effected by developing the expression for the perturbing forces into a series depending upon their powers and products, the principal dif ficulty is experienced in the evaluation of two consecutive quadratures, the first of which is ordinarily performed by means of a series depending upon the sines and cosines of the eccentric anomaly. This method, however, becomes inapplicable in the case of comets whose orbits are ordinarily very eccentric. In order to meet this case, Hansen has invented the method of partitions, in which he divides the comet's orbit into successive portions, and introduces into them new variables called partial anomalies; the variables for one partition being connected with those of the next by a discontinuous function. Professor Gyldèn's method consists in modifying that of Hansen, by introducing an elliptic

integral in place of the discontinuous variable, by means of which, it is said, he is able to compute the perturbations with ease, even in the most difficult cases.-6 B, LXXX., 808, 907, 1070.

SPECTRUM OF COGGIA'S COMET.

Some accurate observations of the spectrum of Coggia's comet of 1874 were made by Bredichin, of Moscow. The greater part of his work was done by means of a spectroscope by Merz. The values of the scales used by him were determined each night by comparison with a Geissler's tube. The channels observed in the cometary spectrum coincide with those of the bands in the spectrum of the hydrocarbons, whose wave lengths are respectively 563.3, 516.4, and 474.2. -Bullet. de la Soc. Imp. des Naturalistes de Moscou, 1874,

146.

THE PERIODIC COMET OF d'arrest.

The periodic comet of D'Arrest was discovered in 1851 by that astronomer. Its orbit about the sun was computed with considerable precision by Villarceau, who allowed for some of the perturbations to which it was subjected by the attractions of the planets. His work has been recently taken up by Le Veau, and carried to a considerable degree of refinement; the inclination of the plane of the comet's orbit to the plane of the ecliptic is only fourteen degrees. A special difficulty, however, arose from the fact that in 1861 the comet approached very near to the planet Jupiter, and the influence of this great body was so considerable that the variations in the perturbations were sensibly of the same order as the changes in the elements of the comet's orbit, so that, in order to obtain the corrections to the latter, the ordinary equations of condition would not suffice. This difficulty was overcome by employing the method of false position. The twenty-two resulting equations were resolved by the method of Cauchy. The mass of Jupiter employed in these computations is that deduced by Bessel from observations of the satellites of that planet; and the results of Le Veau's observations show that no material change in the mass of Jupiter is needed, although the new observations of this comet at its successive apparitions will probably enable the astronomer

to determine the mass of that planet with very great exactness.-6 B, LXXXI., 141.

THE LUNAR THEORY.

The theory of the movements of the moon, which has occupied so many astronomers since the days of Laplace, or, more correctly speaking, since the days of the earliest Chaldean observers, has most recently received some additions by the labors of Schjellerup, who has paid especial attention to the acceleration of the moon's mean motion, and the identification of the eclipses that are recorded by the ancient astronomers. Schjellerup has especially sought for confirmation of his investigations by computing the eclipses recorded in the Chinese classics, as published by Dr. Leggie. Among the eclipses subjected by him to computation are those which occurred 708 years B.C., 600 years B.C., and 548 years B.C. -Oversigt Kongelige Danske vid. Selsk., 1874, 61.

ASTRONOMICAL OBSERVATIONS AT MANNHEIM.

In the volume of astronomical observations at Mannheim, recently published by Schönfeld, he gives the observations of nebulæ and stellar clusters that have been made by him since 1862, amounting in all to eight hundred and twenty complete measurements of the distances between nebula and neighboring stars. His object has been to determine the positions of as many nebulæ as possible, as accurately as he could by measuring micrometrically their distances from neighboring stars. In this work, in which he was almost the only observer twenty years ago, others have also become active since then, and have even surpassed him in the quantity of work done, though not in quality.

The condition of the atmosphere has been carefully noted by him at each observation. The constant differences between his own positions and those of other observers, such as Schultz, are very small.-Astron. Beob. auf der Grossen Sternwarte zu Mannheim, Dr. E. Schönfeld, 2. Abth., 1875.

ASTRONOMICAL OBSERVATIONS AT MILAN.

The recent publication No. 5, from the Royal Observatory at Milan, contains various astronomical observations, among which are especially prominent the photographic plates rep

resenting Coggia's comet of 1874, a chart of the Pleiades, and a lithographic plate representing the phenomena of the lunar eclipse of the 1st of July, 1863. In the latter the varied colorings of the portions of the disk of the moon are very striking. In the chart of the Pleiades, the nebula around Merope is represented as very distinct. There seems to be good reason to doubt the variability of this object. The series of drawings of the comet of 1874 appears to be remarkably complete, and is very skillfully executed.

THE GREAT PARIS TELESCOPE.

The great telescope at Paris is now quite complete, except in a few minor matters. It was officially exhibited on the 7th and 9th of October. The mirror is 47 inches in diameter, with a focal distance of 23 feet. The weight of the mirror is half a ton; it is constructed of glass, and is silvered by the Foucault process. A metallic mirror of the same size would probably weigh four tons. The cost of the mirror was £2000. The telescope is mounted like an ordinary equatorial refractor. A magnifying power of 500 has been found to answer excellently for observing minute stars. The finder, together with the ocular and the small plane mirror, are all placed at the front of the tube, and can be rotated around its axis, thus facilitating the use of the large iron winding staircase from which observations may be made. The height of this staircase is about 40 feet, and its weight six tons. It rests on two circular iron rollers, and is always placed on the same side of the tube as the counterpoise. It is moved by special machinery. The observations are made in the open air, but the instrument is protected at other times by means of an iron house, which building weighs twelve tons, and is movable on rollers by means of special machinery, so that it can be rolled to one side, and in less than a quarter of an hour the huge telescope can be uncovered and pointed upon any object, however minute. The entire cost of the telescope and appurtenances has been £8000, and it has occupied six years in building, the work having been interrupted several times by the events of the civil war and other matters; its final accomplishment is due to Le Verrier's perseverance. This distinguished astronomer now contemplates undertaking a large refractor,

having a focal length of about 55 feet. Its construction will probably occupy three years. The appropriation initiating this new work has already been made.-12 A, XIL, 538.

LARGE TELESCOPES.

It is announced that the principal refractor of the new observatory at Vienna is to be manufactured by Grubb, of Dublin, the order for its execution having already been given. The object-glass will have an aperture of about 27 inches, according as the disks of glass turn out, these latter being manufactured in Paris. The axes will all have their friction relieved by anti-friction apparatus. The tube will be entirely of steel; and all the various motions of the instrument, as well as the readings of the different circles, will be available to the observer from the eye end. The telescope will be mounted completely at Mr. Grubb's new workshops, and covered by a corrugated iron roof fifty feet high. The latter is but a temporary structure; outside of it will be erected a splendid steel dome originally designed by Mr. Grubb, which, after being tested at Dublin, is to become in Vienna the permanent shelter of the mounted refractor.12 A, XII., 517.

THE SPECTROSCOPIC OBSERVATORY AT CALCUTTA.

Rev. E. Lafont, Rector of St. Xavier's College at Calcutta, has addressed the President of the Asiatic Society of Bengal a letter in which he says he proposes to erect a spectroscopic observatory at the college, where daily observations and maps of the solar protuberances will be made. As this undertaking is entirely for the benefit of science, he ventures to request such assistance and subscriptions as may be necessary. The total sum required is about ten thousand reals, toward which the council of the society has contributed five hundred. He states that the pressing invitation of his friend, Professor Tacchini, first induced him to attempt the estab lishment of a spectroscopic observatory.-Proceedings of the Asiatic Society of Bengal, February, 1875.

THE SOLAR ATMOSPHERE AND RADIATED HEAT.

Mr. John Ericsson has published a portion of his solar investigations in a special memoir (privately printed in New