Electric Current on the Photo- Electric Effect. 



917 



be obtained from a plate. However, it was finally roughly 

 determined that for any given plate current the photo- 

 electric current increased up to a maximum, beyond which 

 it did not go unless a larger plate current was used. With 

 very high currents this maximum was followed by a fairly 

 rapid decrease in the photo-electric current. The rises of 



Fig. 1. 



E-^E 



Q, quartz plate; E, copper electrode, with ebonite cover, connected to 

 electrometer; B, bismuth plate: A, battery leads; P, connexion 

 to pump. 



the photo-electric current were always very slow, in some 

 cases occupying up to two hours to attain the maximum. 



When the plate current was stopped, the photo-electric 

 current at once started to decrease, at first quite rapidly, but 

 apparently it never drops to exactly the original zero, usually 

 going beyond it. 



