EFFECT OF LIGHT ON ELECTRICAL CONDUCTIVITY OF SELENIUM. 371 



100 cms., B for red at 300 cms., C for red at 600 cms., D 

 for green at 200 cms., and E for the intensified green light. 



Fig. 4. 



•4 



V 









\\ c 









\ \b"^s 





^— L_ 





XA 





r^-L- 













I' 2 3' 



The rate of recovery is seen to be greatest for the most 

 intense light and just as in the case of the rise of conduc- 

 tivity upon exposure to the light, the curves for green show 

 a more rapid rate of fall at the start, becoming slower 

 relatively to the red as the time advances. This however 

 is due in part to the fact that the duration of the exposure 

 when using green light was longer than with red, the ex- 

 posure being continued in all cases until the conductivity 

 was practically steady for several minutes. Each curve 

 represents the mean of several trials, and with red light the 

 exposures lasted from five to ten minutes, and with green 

 from ten to twenty minutes. The differences in the rates 



X— Nov. 3, 1909. 



