A. MATHEMATICS AND ASTRONOMY. 15 



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 ob- 

 servations. Among the defects experienced in the use of 

 this thermometer is its liability to be influenced by reflec- 

 tion from neighboring: bodies. The reflection from the il- 

 laminated 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. 



SOLAE EADIATIOX. 



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 davs, 

 the actinometric power varies ; and, according to the ob- 

 servations at Montsouris, while it is theoretically in De- 

 cember 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 (7, 

 VIII., 114. 



STUDIES OX SOLAE EADIATIOX. 



M. Desains has attempted to resolve an important meteor- 

 ological problem : viz., to determine the total weight of the 

 vapor of water contained in the atmosphere in a given re- 

 gion. 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 



