at the total solar Eclipse in 1882 



375 



In this equation f is the transmission coefficient of the 

 atmosphere ; therefore /is really the solar constant expressed 

 in cubic centimetres water evaporated per square metre per 

 minute. Under g it is given in gr. C. per square centimetre 

 per minute, for ,^=o-O535/ Calculating back, we obtain the 

 observed values of the intensity of the sun's rays at the sea- 

 level corrected only for the sun's zenith distance, h = \f. 

 This is expressed in cubic centimetres water evaporated per 

 square metre per minute, and it is unaffected by the value 

 employed as the transmission coefficient of the atmosphere, 

 because this is eliminated in the process of reduction. 



The numbers in this table show that the values of the 

 heating effect of the rays of the vertical sun, deduced from 

 observations made when the sun was at zenith distances 

 ranging between 10 and 44, are practically identical. 



If we take one horse- power per square metre as the 

 intensity of the rays of the vertical sun at the sea-level, their 

 intensity outside of the atmosphere is 1-5 horse-power per 

 square metre, using Herschel's value for the transmission 

 coefficient. This is equivalent to 15,882 gr. C. per square 

 metre, or 1*588 gr.C. per square centimetre per minute. In 

 round numbers we obtain I '6 for the value of the solar con- 

 stant. While it is possible that this value may be a little too 

 low, reasons are given in the paper for believing that the 

 values commonly received, which lie between 3 and 5 gr. C. 

 per square centimetre per minute, are much exaggerated. 



