KEPOKT OF THE SECRETARY. 



83 



and 1910. Station was reached on July 31, 1911, but owing to a most 

 unfortunate miscarriage of a box of apparatus, observations could 

 not be commenced until August 26, and several more days were re- 

 quired to get the whole outfit working satisfactorily. The weather 

 of August was excellent at both Mount Wilson and Bassour, but in 

 the subsequent months the good days at one station frequently coin- 

 cided with bad ones at the other. Hence, although 44 days of solar- 

 constant observations were secured at Bassour up to November IT, 

 when the camp was broken up, and a still greater number were 

 secured at Mount Wilson, only 29 of these coincided. 



In spite of the loss of August and the unfavorable weather of sub- 

 sequent months, the results thus far reduced strongly confirm the 

 supposed variability of the sun. For example, the first half of 

 September yielded the following results : 



Solar constant values. 





Aug. 29. 



Aug. 30. j 



Vug. 31. 



Sept. 1. 



Sept. 2. 



Sept. 3. 



Sept. 4. 



Sept. 5. 



Sept. 6 



Sept. 7. 





1.913 

 1.976 



1.890 

 1.952 



1.912 

 1.945 







1.894 

 1.966 



1.872 

 1.905 



1.866 



1.935 



1.904 





1.930 



1.933 



1.916 











B. W 



.053 



.062 



.033 







.072 



.033 







.012 

















Sept. 8. 



Sept. 9. 



Sept. 10. 



Sept. 11. 



Sept. 12. 



Sept. 13. 



Sept. 14. 



Sept. 15. 



Sept. 16. 





1.960 



1.945 

 2.015 



1.872 

 1.860 



1.835 



1.865 

 1.905 





1.885 



1.867 

 1.885 



1.890 





1.895 















B.-W 





.070 



-.012 





.040 







.018 





























From these results appear : 



(A) The solar constant results obtained at Bassour are on the 

 average 2 per cent higher than those obtained for the same days on 

 Mount Wilson. Referring to former reports, the solar constant re- 

 sults obtained at Washington and at Mount Whitney were also con- 

 sistently higher than those obtained at Mount Wilson, and by about 

 the same amount as just given. Hence, we seem justified in consider- 

 ing that there is a condition tending to low results prevailing at 

 Mount Wilson. This may very probably be the increase of haziness 

 there at high sun, due to increased humidity. In view of the uniform 

 testimony of the three other stations, it seems proper to conclude that 

 Mount Wilson solar constant values are generally too small. 



(B) High solar constant values at Bassour correspond with high 

 solar constant values at Mount Wilson, and vice versa. This relation 

 is shown in both the accompanying diagrams. Figure 1 is a plot of 

 the successive solar constant values at the two stations for the days 

 mentioned. Figure 2 shows the same values plotted in a manner to 



