366 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



dm 7 , 



The measurements show that this relation does not hold, even for 

 spheres of radius 0.5 millimeter or more. The observed values do, 



Figure 1. Evaporation from small spheres of Iodine. Small circles, 

 observed values. Large circles, calculated values. 



however, agree accurately with the assumption that the rate of evapora- 

 tion is proportional to the surface and at the same time inversely as 

 the radius, so that 



dm , s dm 1 , 



j- = k - or =- = k'jVit 



at r dt 



In the figure the large circles have been placed according to the 

 formula 



A — irnA 



m^ 



m^ 

 tz — t\ 



= K, 



