IIS SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 66 
As in former years a principal object of these investigations was 
to detect and measure changes in the amount of solar heat. Results 
of the now fully reduced work of 1913 and 1914 show that in 1913 
(a time of extremely low solar activity as indicated by the numbers 
of sun-spots, faculz, etc.), the sun’s output of radiation was nearly 
Fic. 141.—Observing station of Astrophysical Observatory on 
Mount Wilson with new tower telescope. Photograph by Abbot. 
three per cent below normal, and that with the return of activity in 
1914, the output of radiation rose to about one per cent above 
normal. The work of 1915, not yet fully reduced, seems to indicate 
that high values will be found to prevail in this year also. 
Fluctuations of solar radiation from day to day, while noted, appear 
to have been less marked in 1914 than in earlier years. 
