ANALYSIS OF SOLAR RECORDS 



73 



ened and presenting a known area to the sun's rays. Built on such a princi- 

 ple, the bolometer invented by Langley and improved by Abbot and the 

 silver disk pyrheliometer invented by Abbot have enabled us to secure since 

 1918, and to some extent before, exceedingly accurate measures of the amount 

 of heat coming from the sun to the outside of our atmosphere ; as well as the 

 amount absorbed by our atmosphere, in a few favorable locations, and the 

 amounts reaching the ground. The intensity at mean solar distance, out- 



Months 



1 1 1 1 1 1 1 1 1 r— t I | 



10 20 30 



1918 



1920 



I r 



o 



1930 





a 



li_i 



j i 



Months 



7 8 



21 



25 



Relative 

 frequency 



(weir ' 



400 



300 

 200 

 100 



5 6 7 8 9 10 II \Z 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 



Months 



Fig. 31 — a. Chrono-periodogram of Abbot's radiation curves analyzed by 

 cyclogram methods. 



b. Abbot's cycles in same. 



c . Frequency periodogram monthly sunspot numbers, 1750-1934. 



side of our atmosphere, is known as the "solar constant" and its average in 

 standard units is usually given as 1.94 calories per square centimeter per 

 minute. 



