191 1-] ABBOT— SOLAR CONSTANT OF RADL\TION. 245 



the observing station, up to the liighest altitude tested, 4,420 meters. 

 Fluctuations in the values proceeding step by step, day by day, from 

 higher to lower values and return, within a range of about 8 per cent, 

 usually occur in somewhat irregular intervals of from five to ten 

 days in total period. These fluctuations are thought to indicate a 

 true variability of the sun. It is proposed to test this conclusion by 

 daily observations extending over several months, and to be made 

 simultaneouslv in California and southern ^Mexico. 



