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 77°, 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, 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.

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

sun.

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

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.

THE 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 THE 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