682 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



2, Change in Transmlssioji accompanying Change in Intensity of 



Incident Radiation. 



The metals used in the following experiments were platinum, 0.0014 

 cm. thick ; copper, 0.0044 cm.; silver, 0.0019 cm.; tin, 0.0012 cm.; 

 aluminium, 0.027 cm. The method was the same in all cases except 

 for differences in detail. The experiment with silver will serve as an 

 example. 



TABLE III. 



Effect of Variation of Intensity upon Transmission bt Silver. 



The tube was placed as far as convenient from the instrument (42 cm. 

 from the platinum of the latter to the centre of the target), and a " ratio 

 of transmission " was obtained by dividing the deflection taken when the 

 screen was in by the mean of two standardizing dctiections taken when 

 the screen was out. Then the tube was moved toward the instrument 

 a distance of 20 cm. along a track wiiich had befen carefully aligned 

 with the instrument before the latter was jacketed, and a determination 



