﻿548 Dr. J. Robinson on the Photoelectric 



approaches a maximum value as the potential difference 

 between the film and the walls o£ the vessel increases, so as 

 to drive electrons away from the film. Also in all but one 

 case it is noticed that there is no inverse photoelectric effect, 



Fig-. 5. — Film of 18 minutes. 



+8 +12 +l6 



Fig. 6. — Film of 55 minutes. 



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which shows that the influence of reflected light can be 

 neglected. Here, again, as in the case of the velocities, an 

 influence of the thickness o£ the film is noticeable. For thin 

 films the maximum photoelectric current is larger for emer- 

 gent than for incident light, and for thick films the reverse is 



