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graph of the solar spectrum yet obtained, but has succeeded in getting an admirable photograph of the spectrum of a star. It will thus become possible to study any changes that may take place in the constitution of the stars or the sun by the comparison of these photographs with such others as may be taken at some future time.-12 A, X., 255.

ZÖLLNER'S THEORY OF THE SOLAR SPOTS. The theory of Zöllner as to the constitution of the sun and its spots has been thus described by him: The sun is a glowing liquid body, surrounded by a glowing atmosphere; in the latter, at a certain distance above the fluid surface, there floats a covering, constantly renewing itself, of shining clouds, like our own cumuli. At those places where the cloud canopy is thinned, or dissipated, there arise on the glowing surface, by reason of powerful radiation, the slag-like products of cooling. These, therefore, lie deeper than the general level of the shining clouds, and form the nuclei of the sun spots. Above these cooled regions there are formed descending currents of air, which give rise to a circulation of the atmosphere around the edges of the islands of slag, to which circulation the penumbra owes its origin. The cloud-like results of condensation, which are formed within the region of this circulation, have their shape and temperature determined by the nature of the circulation itself, and must, therefore, in consequence of their lower temperatures, appear less brilliant than the other portions of the cloud canopy of the solar surface, and seem depressed like a funnel, by reason of their descending motion above the spot. The exterior edge of the penumbra is at the level of the shining canopy:-Poggendorfj° Annalen, CL., 300.

ANCIENT OBSERVATIONS OF SOLAR SPOTS. In the 29th volume of the meteorological observations at Lyons, France, an account is given of some early observations of the solar spots made by Father Berand. In 1741, on the 8th of April, he observed eight pretty large spots on the sun. From the 16th to the 30th a remarkable spot fixed his attention. It was composed of an obscure portion of irregular form, situated between two black points, the whole enveloped by a brown cloud composed of small black

points. The whole had a round form, whose apparent diameter was 55 minutes of arc, or three times the diameter that the earth would appear to have if placed at the same distance.-13 B, III., 134.

THE SOLAR ATMOSPHERE. Zöllner has published in detail his defense of his views as to the nature of the solar spots, basing his reasoning principally upon laws announced by Kirchoff in his investigations of the solar spectrum. He first shows that if the lowest strata of the solar atmosphere radiate as intensely as they absorb, clouds in that atmosphere will be scarcely distinguishable, so far as any difference of brightness is concerned between them and the neighboring atmosphere; and, secondly, he states that it is not sufficient to assume the existence of clouds, but that some reasonable cause must be assigned for their continued existence for weeks and months. In his exhaustive analysis he shows that local cooling can not be explained by conduction of heat, and that, therefore, up-rushing or down-rushing currents of cooling gas can not be produced by this cause. The influence of radiation being thus the only resource left, he draws analogy between the solar spots and the formation of dew in the earth, and seeking those circumstances under which the radiation from the surface of a body is localized for the longest time, he finds that such radiation proceeds most freely when the body is a solid; hence he concludes the solar spots to be of a solid nature.--Poggendorff Annalen, CL., 298.

THE DIMENSIONS OF TIIE SUN.

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Some of the results of the studies of Secchi having been severely criticised by Anwers, he has recently edited a work by Father Rosa, which will, in part, serve as an answer to these criticisms. The investigations of Rosa and Secchi are based upon observations made during the past hundred years at Greenwich, Dorpat, and Königsberg, and Secchi believes that they show that the body of the sun must be considered as consisting of two quite independent masses, viz., a solid nucleus, surrounded by an atmosphere of gas. Instead of the solid nucleus, we may also understand the central portion to be a mass of gas in such a state of condensation that it is to a great extent independent of its lighter envelope. The photosphere, according to these authors, is subject to periodical variations, which are not directly due to the force of gravitation. The force which specially deforms the photosphere is intimately connected with that which affects the secular movement of the centre of gravity of the sun, as has been shown by Le Verrier. The secular changes of the photosphere and of terrestrial magnetism are subject to a simultaneous oscillation of sixty-six and two-third years, similar to that equal period to which the perigeum of the apparent solar orbit is subject.—19 C, VIII., 33.

ON SOLAR RADIATION. One of the most comprehensive investigations into the subject of solar radiation is that recently published by the Rev. F. W. Stowe, based on five years' observations at twenty-five stations, with the black bulb maximum thermometer in vacuo, freely exposed to the sun and air at the height of at least four feet. By the amount of solar radiation, he understands the excess of the reading of the solar thermometer above that of the ordinary maximum thermometer placed in a double - louver screen. Incidentally he mentions that the solar thermometer seldom reads above 140° Fahr. in England, and that 134° is the highest temperature on his records. The radiation attains its maximum in May. This is to be attributed to the prevalence of northerly winds, and consequent dryness of the atmosphere. December is the month of least radiation. In this statement we take account only of the maximum amounts of radiation during clear days in those months. The western stations in England show more radiation than the easterly ones. The neighborhood of the sea appears to somewhat diminish solar radiation during the summer, which he attributes to the fact that the air from the sea is, for the most part, heavily loaded with vapor during the summer season. The excess of radiation at western stations, he is inclined to attribute to the greater purity and coolness of the air, and its freedom from haze. As regards secular change, he found the radiation decidedly in defect in the early summer of 1870, but in excess in 1872, a result which may have resulted from the presence of a colder stratum of air in unsettled weather, and in part, also, from increased reflection from the clouds. In speaking of the defects of the solar thermometer as a means of measuring the intensity of solar radiation, he states that when a perfect actinometer is proposed for general use by meteorologists, the blackened bulb in vacuo must give place to it; but in the mean time it is the best instrument that can be used for ordinary observations. Among the defects experienced in the use of this thermometer is its liability to be influenced by reflection from neighboring bodies. The reflection from the illuminated side of a cloud is very great. In this respect, Mr. P. Harrison stated that he was able to confirm Mr. Stowe's conclusions. — Quar. Jour. Meteor. Society of London, II., 205,

SOLAR RADIATION. At the physical observatory at Montsouris, near Paris, regular observations are made of the radiation of the sun by means of a simple actinometer. If the atmosphere were perfectly diathermanous and the days of uniform length, the average power of the sun, allowing for its varying distance, would be the same throughout the year, and may be placed at 100°. But through the influence of the variable amount of moisture and cloud, and the variable lengths of the days, the actinometric power varies; and, according to the observations at Montsouris, while it is theoretically in December about 31°, and in June 770, of our arbitrary scale, it was actually observed to be in December 29°, and in June 68°, showing that the earth received during those months in 1873 and 1874 slightly less heat than the average.-19 C, VIII., 114.

STUDIES ON SOLAR RADIATION. M. Desains has attempted to resolve an important meteorological problem : viz., to determine the total weight of the vapor of water contained in the atmosphere in a given region. He has made preliminary observations at Lucerne and Rigi Culm, and from these he deduces the absorption of solar heat due to a thickness of one centimeter of water. He states that, by a long-continued series of observations of a similar kind, he hopes to be able to compile hygrometric tables which will give, for any observed intensity of solar radiation, at two stations, the corresponding total weight of the vapor of water contained in the entire atmosphere. At Paris he finds, for instance, that for equal thicknesses of air its diathermancy varies from * to so, which variations are greater than those which would have been obtained by interposing or removing a screen of water one centimeter thick.-2 B, XXXIV., 230.

MEASURING THE CHEMICAL ACTION OF SUNLIGHT. Dr. Phipson says that many years ago he made some experiments on the measurement of the chemical action of the solar rays, and described an accurate method of effecting it. Having discovered that a colorless solution of molybdate of ammonia in sulphuric acid became greenish blue when exposed to the sun, and colorless again during the night, and that the amount of chemical action exerted to produce this tint may be accurately determined by using a dilute solution of permanganate of potash, he suggests that, in order to possess a perfectly accurate process by means of which to determine the chemical intensity of solar light, we have only to expose always the same quantity of the substance to the light for the same period of time, and then determine the tint produced therein by the action of the sun's rays.--18 A, XX., 124.

THE TEMPERATURE OF THE SUN.

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The two methods of making the measurements of solar heat may be described as the dynamic method and the static method. The former is that on which the pyrheliometer of Pouillet is based; in which method a thermometer is exposed alternately in the shade and in the

In the static method the thermometer remains permanently subject to solar radiation; until the temperature indicated by it becomes stationary, at which time the temperature of the thermometer and that of the inclosure are noted. The principle on which the static method is founded has been investigated by Vicaire, whose results have lately been further modified and improved upon by Violle, who shows how to take account of the diameter of the bulb as well as its own radiation; he has made investigations into

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