16 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



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 -ffc to T 8 o, which variations are 

 greater than those which would have been obtained by in- 

 terposing 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 ex- 

 periments 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 molyb- 

 date 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 pyrhe- 

 liometer of Pouillet is based ; in which method a ther- 

 mometer is exposed alternately in the shade and in the 

 sun. In the static method the thermometer remains per- 

 manently subject to solar radiation; until the temperature 

 indicated by it becomes stationary, at which time the tem- 

 perature 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 



