74 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



mechanical device, could be made to follow the changes in the 

 position of the sun. The screen was blackened on the side turned 

 towards the instrument and covered with white paper on the other 

 side. The screen itself was to no appreciable degree heated- by the 

 sun radiation. 



In figure 13 the observations are plotted as ordinates in a dia- 

 gram where the time of the day is given by the abscissae. The more 

 the sunlight — and therefore also the scattered skylight — is cut off 



Fig. 13. — Radiation observed during total eclipse August 20, 1914. 



by the shadowing body of the moon, the more the effective radiation 

 to the sky naturally increases. From what has been said above it is 

 clear that we are right in comparing the radiation during the total 

 phase only, with the values obtained during the night. The feeble 

 radiation from the corona is perfectly negligible and causes no com- 

 plications. The mean radiation during the totality is found to be 

 0.160. At the same time the temperature of the surrounding air was 

 13.6 , the humidity as given by the Assmann psychrometer, J.J mm. 

 A comparison between the value of the effective radiation during the 



