720 



TABLE 810.— THE SOLAR CONSTANT, MONTHLY AND YEARLY MEANS* 



* Calories per cm per min. 



TABLE 811.— AIR MASSES 



The transmission, both total and spectral, of the atmosphere depends upon several vary- 

 ing factors besides the actual air masses, that is, the length of the path of the rays in the 

 atmosphere ; thus, corrections must always be determined for different tests. 



Values of the transmission of the atmosphere for any position of the sun except when it 

 is directly overhead are calculated from measurement when the sun is in the zenith, i.e., 

 e m = eoa m when c m is the intensity of the radiation at air mass m, e<> the intensity for the 

 sun in the zenith, and a the transmission for unit air mass, m is unity when the sun is in 

 the zenith and approximately equals the secant of the zenith distance for the other positions. 



Besides values derived from the pure secant formula, the table contains those derived 

 from various other more complex formulas, taking into account the curvature of the earth, 

 refraction, etc. The most recent is that of Bemporad. 



SMITHSONIAN PHYSICAL TABLES 



