no. 3 



RADIATION OF THE ATMOSPHERE ANGSTROM 



151 



The local time of each observation, from which the sun's zenith angle and 

 finally the corresponding air mass was computed, was determined from the 

 readings of three watches. Before and after the expedition to Mount Whit- 

 ney, the watches were compared with the daily telegraphic time signal at 

 Claremont, Cal. The time is probably accurate within half a minute. 



•45 .50 .55 -6o 



Fig. 16.— Transmission curve of absorbing screen. 



.65 11 



The results are given in tables 17 and 18. Table 17 refers to the measure- 

 ments of the total radiation and contains : (1) the date, (2) the local apparent 

 time (t), (3) the computed air mass (w), (4) readings of the milliammeter 

 ( s )> (S) the total radiation computed from the readings. Table 18 contains the 

 same quantities relating to measurements taken with the absorbing screen. 



Bemporad's * expression for the air mass in terms of the apparent zenith 

 angle was employed. His values for 60°, 70 , 8o°, and 85 were available in 

 a short table given by F. Lindholm. 2 The differences between these values 

 and the secant of the angle give the (negative) corrections to be applied to 

 the secants of these angles. Through these values of the correction an alge- 

 braic curve of four terms was passed and the correction was then calculated 

 for other angles. In obtaining the apparent zenith angle, allowance was made 

 for refraction. 



1 Mitteilungen der Grossherzoglichen Sternwarte zu Heidelberg, No. 4, 1904. 

 a Nova Acta Reg. Soc, Sc. Upsal., Ser. IV, 3, No. 6. 



