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the temperature of the sun, the radiation of the sky bordering the sun, and the general absorption of the solar atmosphere.—7 A, XLVIII., 158.

VARIABILITY OF SOLAR TEMPERATURES. Mr. Blandford, of Calcutta, gives the results of his studies into the variability of solar temperatures as indicated by the maximum black bulb in vacuo solar thermometer. Mr. Blandford's investigations are based upon observations made from 1868 to 1874 at stations in India, and his results seem very striking, if not absolutely conclusive, as to the direct variation of the solar heat with the number of the spots and prominences. The absolute maximum temperature of the sun seems, according to his diagram, to have been reached in February, 1871. Unfortunately the highest sun temperatures recorded by his thermometers occurred not on days that were cloudless, with a very dry atmosphere, but on those in which there was a considerable proportion of cloud and frequent rains. The effect of the heat reflected from the edges of the cumulus clouds upon his thermometers seems not to have been duly considered by him.

TUE TEMPERATURE OF THE SUN. An improved method of investigation to determine the temperature of the sun has been put in execution by Violle, who describes his apparatus as consisting essentially of two concentric and spherical envelopes of brass. In the centre of the interior one is the bulb of the thermometer, while between the two envelopes a continuous current of water circulates. The exterior surface is highly polished, while the interior surface of the interior sphere is covered with lampblack. The experiment is conducted by first determining the temperature shown by the interior thermometer without exposure to the sun and then the temperature as shown during the exposure to the sun and after it has become stationary under the influence of the solar rays. The conclusions that can be drawn from this apparatus depend upon the employment in succession of different thermometers and different apertures of the diaphragm which allows the solar rays to fall upon the thermometer, Violle has made a very careful investigation into all the influences which can affect the indications of the thermometer, and from some preliminary experiments finds that the temperature of the sun, after making the correction for the absorption of the terrestrial atmosphere, is 1354° Centigrade.--7 A, XLVIII., 236.

THE TEMPERATURE OF THE SUN, We have already mentioned the interesting researches of Violle upon the measurements of the temperatures of the heavenly bodies, and have now to record a preliminary but very approximate result arrived at by him for the temperature of the sun, the correction being made for the absorptive influence of the earth's atmosphere. He defines the true temperature of the sun as that which must be possessed by a body of the same apparent diameter as the sun in order that, endued with an emissive power equal to the mean emissive

power of the sun, it may emit in the same time the same quantity of heat as the sun. The observations made by his instrument, described in the previous note, by a method which he characterizes as the dynamic method, have enabled him to determine the emissive power for heat of steel after fusion, just as it issues from the Martin-Siemens furnace, and he finds it corresponds to a temperature of 1500° Centigrade. If now we assume that the mean emissive power of the sun is sensibly equal to that of steel in fusion, we arrive at the value of 2000° Centigrade for the true temperature of the sun's surface.—7 A, XLVIII., 396.

REFLECTING POWER OF TIJE PLANET MERCURY. Zöllner has extended to the planet Mercury a series of photometric observations similar to those made by him some years ago upon the moon. The observations made, upon two especially favorable evenings, gave him, for the relative brightness of Jupiter and Mercury, the ratio 2.7 in one case, and 3.2 in the other. A comparison of the peculiarities of the results for Mercury and the moon leads him to the conclusion that Mercury is a planet whose superficial condition very nearly agrees with that of the moon; that also, like the moon, it probably possesses no atmosphere. The reflecting power, or albedo, of Mercury is the least of all the planets, and even less than that of

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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, wliatever 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 energetic 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.

TIE 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

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