the moon. Zöllner also makes a very ingenious attempt to determine the albedo of the earth, and the law of the variable intensity of the light that will be exhibited by it, in its various phases, as seen from a distant planet. Concerning his attempt to determine this albedo through observations of the dark limb of the moon, he states that, although the results can scarcely be accepted as having much accuracy, they nevertheless show the practicability of the method.-19 C, 1874, 150.

THE ATMOSPHERE OF VENUS.

Lohse has investigated what would be the effect and appearance of a spherical gaseous mass passing over the solar disk as seen from the earth, and has sought to apply his result to the possible effect of the atmosphere of Venus on the phenomena of the Venus transit. In conclusion, he states, with reference to the so-called black-drop phenomenon, that if the atmosphere of Venus has a density so great that it unites the solar rays in one point lying between Venus and the earth, it must then have the same effect as an opaque body-that is to say, the solar limb will by this atmosphere be broken or indented before the body of Venus itself touches it; and, conversely, the solar limb will not regain its integrity, at the close of the inner contact, until the atmospheric layer is entirely within the solar disk. It is possible that, at the inner contact, this effect of the atmosphere of Venus contributed considerably to the appearance of the so-called black drop.-19 C, 1874, 170.

THE VISIBILITY OF THE PLANET VENUS.

Professor Safarik, of Prague, endeavors to explain the intense brightness of Venus, and particularly the dazzling splendor of her bright limb, without assuming specular reflection on the surface of the planet. He remarks that the intensity of the phosphorescence of the sea in our tropical waters is not fully appreciated by the near observer, who therefore has only a faint idea of the intensity which this phenomenon can acquire under highly favorable circumstances, and the author thinks it not unreasonable to suppose that such a phosphorescence can be seen even at the

distance of Venus. If so, it explains the fact that the edge of the dark limb of Venus is seen brighter than its central part; for it is demonstrable by calculation and confirmed by observations that a rough surface reflecting diffused light appears the brighter the more obliquely it is regarded. Report Brit. Assoc., 1873, 408.

THE TIDAL RETARDATION OF THE EARTH'S ROTATION.

In some remarks on the various causes that operate to retard or accelerate the earth's daily rotation, Mr. Mallet remarks that if we take into account all the operations at work upon the earth's surface, such as the flowing of rivers down hill into the ocean, the carriage of great masses of earth, as mud, from the upper sections of the earth to the bottom of the ocean, the fall of raindrops, the flow of rivers from low to high latitudes, and all other similar seemingly insignificant causes, we shall find no reason to suppose that the retardation of our globe by tidal friction, whatever may be its actual amount, can go on unchecked until the earth is brought to a stand.-7 A, XLVII., 40.

THE MASS OF JUPITER.

Powalky has attempted a new determination of the mass of the planet Jupiter, by examining its perturbing influence on the movements of the asteroid Virginia (No. 50). The result to which he is led indicates that the mass of Jupiter should be increased by about one two-hundred and seventysecond part of the present adopted value; but although this correction enables him more nearly to satisfy the observations that have been made upon Virginia, he is yet inclined to attribute to it only a slight value, and hopes to attain better results by a repetition of his work in future years. -Astron. Nach., LXXXIV., 71.

THE SATELLITES OF URANUS.

An interesting study has lately been made by Professor Holden, of the Washington Observatory, on the observations of Sir William Herschel upon the satellites of Uranus. It is well known that the latter astronomer announced sixty years ago that Uranus was accompanied by six satellites; but of the existence of four of these there has always been

considerable doubt, since no one was ever able to confirm the observations of Herschel, In 1847 Lassell discovered two interior satellites, which were, however, different from those which Herschel suspected; and since that day the four problematical satellites of Herschel have been generally discarded by astronomers. Professor Holden now brings testimony to the high excellence of Herschel's observations, as, by computing backward, he has shown that probably this distinguished astronomer actually observed the two interior satellites of Lassell (named by him Ariel and Umbriel); but that he was unfortunately prevented from identifying them as satellites because his telescope could not show them on two successive nights. The extreme difficulty of observing these objects makes us wonder at the marvelous skill and patience manifested by the elder Herschel in this laborious research, which was carried on by him from 1787 to 1810.-Bull. Phil. Soc. Washington, Appendix IV.

ORIGIN OF AEROLITES.

During the last two or three years the discovery of ener getic forces of eruption on the sun has demonstrated the occasional occurrence of convulsions so violent that they may suffice to project molten and gaseous matters to distances beyond the sphere of the sun's attraction. The existence of such forces and the evidence which the microscope affords that aerolites have had their origin among mineral masses in a state of fusion, if not of vapor, combine to support the theory, formerly entertained by other writers and recently announced very definitely by Mr. Proctor in England and Professor Kirkwood in America, of the astro-meteorological hypothesis of the origin of meteors and meteorites.-Report Brit. Assoc., 1873, 400.

THE GREAT COMET OF 1684.

The investigation of the great comet of 1684 forms the subject of the inaugural dissertation of Professor Neugebauer of the University of Breslau. This comet belongs to those which, on account of the close approximation of their orbits to the earth's orbit, have attracted the attention of Professor Schiaparelli as worthy of scrutiny in connection with shooting-stars. The only accurate observations of the comet of

1684 that have come down to us were made during two weeks at Rome by Bianchini; and in order to derive from these the best possible results, Neugebauer has reduced them all anew, by using the best materials available, he having access to original letters and drawings still in existence. The observations made by Bianchini were of the simplest kind; for instance, he would hold a stretched thread in such a position that, while it covered some one of the known fixed stars, it nearly covered the comet itself, whose position, relatively to the ends of the thread, was then estimated by the eye. Other and more exact observations were made with the help of rude instruments. The relative positions of the comet, as deduced by great labor, in general seem to be trustworthy to within a few minutes of arc, and Neugebauer's elements of its orbit are not greatly different from those given by Halley. It follows, as the most interesting result of the investigation, that on the 18th of June, 1684, the distance of the comet from the earth was only the hundredth part of the distance of the earth from the sun, being, in fact, only the thirtieth part of the distance of the earth from Coggia's comet on the 21st of July, 1874, when it was nearest the earth. It seems, therefore, that the orbit of the comet of 1684 approaches more nearly to the orbit of the earth than almost any other known comet, and that under favorable circumstances we shall be justified in expecting some meteoric display yearly about the 18th of June, at which time the earth annually comes into the plane of this comet's orbit.-Inaugural Dissertation, Breslau, 1873.

THE PHENOMENA OF COMETS.

As the result of a suggestive paper by Faye on the forms of comets, he states that he has been led to conclude with perfect certainty that cometary phenomena reveal to us in the heavens the existence of a second force totally different from attraction, and capable of playing an important part, and producing before our eyes gigantic phenomena; that, with great probability, this force is nothing less than the repulsion due to heat. In order to demonstrate experimentally the existence of such a repulsion (which is mathematically deducible from the dynamic theory of gases), he advises the following arrangement: A jar of very rarefied air is il

luminated by means of the spark of an induction apparatus; the glass bell-jar in which the vacuum is to be made is traversed by the two wire conductors of the apparatus, the one vertical and the other horizontal, and the induction spark itself appears in the form of feebly luminous rays, whose colored stratifications surround the horizontal conductor with a luminous sheath of a well-marked blue color. The hori zontal wire having been made of a thin plate of platinum, an independent electric current is passed through it, so as to render it red-hot, and immediately the blue-colored sheath of rarefied air is repelled from the red-hot platinum plate. After having made all possible variations of this experiment, he concludes that it demonstrates a repulsion between the heated platinum and air.—12 A, X., 289.

THE CONSTITUTION OF COMETS.

Mr. Lockyer briefly reviews the state of our knowledge as to the spectroscopic observations of comets. In general, observers seem to agree that these bodies consist, in part at least, of not very dense incandescent vapor, while in some cases very dense or possibly very complex vapors, or even glowing solid substances, seem to have been present. Huggins first suggested the idea that the rarer cometary vapors might be composed of nitrogen, but subsequently suggested the theory that a comet is composed of carbon, and that a temperature prevails high enough to volatilize a portion of this substance, giving rise to the three bands coinciding with those of olefiant gas. Mr. Vogel has, however, shown that this is a very questionable theory, and that we are only justified in concluding that a portion of the light emitted by the comet is its own light, and very probably comes from glowing gas. Mr. Lockyer, moreover, found the nucleus of Coggia's comet deficient in blue rays, whence its temperature must have been low, which conclusion is further justified by the fact that cometary light gives channeled space spectra, which latter are peculiar to low temperatures.-12 A, X., 180.

THE FORMATION OF THE TAILS OF COMETS.

The distinguished Italian astronomer, Schiaparelli, has communicated to the journal of the Italian Spectroscopic Society some studies upon the nature of the repulsive force which