i6 



SMITHSONIAN M LSCELLANEOUS COLLECTIONS 



VOL. OO 



California, on the daily quantity of solar heat. The observations are 

 arranged in such a manner as to indicate not only the quantity of 

 solar heat reaching the earth, but also the quantity of heat which 

 would reach a body with no atmosphere, like the moon. 



So far the observations have indicated that the sun is probablv a 

 variable star having a range of variation amounting to from five to 

 ten per cent within an irregular interval of from five to ten days. 



Fig. 14. — Air. Angstrom and the solar-constant apparatus at Bassour. 

 Photograph by Abbot. 



In loi 1 .Mr. Abbot, assisted by Prof. F. I'. Brackett, observed in 

 Ugeria, while his colleague. Mr. Aldrich, observed on Alt. Wilson, 

 in ( alifornia. The object of thus duplicating the measurements was 

 to avoid any errors due to local atmospheric conditions which might 

 have affected Alt. Wilson observations. As nearly one-third of the 

 circumference of the earth lies between Alt. Wilson and Bassour, it 

 could not be expected that a similar local disturbance could affect 

 both stations at the same time and in the same manner. The observa- 

 tions of i«)i 1 strongly supported the belief that the sun is variable, 

 but owing 1 to cloudiness their number was not sufficient to fullv 



