G A. Butman — Effect of Phosphorescent Material. 139 



recombination of the electrons, which probably takes place 

 quite slowly. 



The acceleration of fatigue with the higher voltages is 

 probably due to the larger amounts of negative electricity 

 taken away, leaving the corresponding positive charge with less 

 negative charge to counteract it. 



Experiments were made on the components of CaBiNa to 

 see if the element which caused the photoelectric effect could be 

 determined so that its properties could be studied without any 

 complications. Thus it was discovered that sulphur gave a 

 photoelectric effect with light longer than 3200 Ang. This 

 was the only one of the components which gave such an effect. 

 Hence, the hypothesis was advanced that the photoelectric 

 effect of the phosphorescent alkaline earth sulphides is due to 

 the sulphur they contain. Experiments are being conducted 

 to test this theory. 



Before concluding, the author wishes to express his thanks 

 to Professor Bumstead, at whose suggestion this investigation 

 was undertaken, for his interest in the work, and to Professor 

 Boltwood for many valuable suggestions. 



Conclusions. 



1. Photoelectric fatigue and recovery is an inherent prop- 

 erty of the material and is due solely to the incident light. 



2. High positive voltages accelerate fatigue with light. 



3. The velocities of the electrons ejected are dependent on the 

 photoelectric state of the material. 



4. The saturation value is dependent on the photoelectric 

 state of the material. 



5. No photoelectric effect can be obtained with CaBiNa 

 with a wave length longer than about 4100 Aug. 



6. Sulphur is photoelectric with lights of a longer wave 

 length than 3200 Ang. 



Sloane Physical Laboratory, Yale University, New Haven, Conn. 



Note. 



In further support of the theory advanced here may be cited 

 the fact recently discovered by the author that sulphur is 

 actinodielectric in addition to being photoelectric* With the 

 apparatus arranged to test for the actinodielectric effect it was 

 found that with red glass cutting off wave lengths shorter than 

 6000 Ang., and with white light through glass, that a deflec- 

 tion was obtained in the direction of the applied field. The 

 field used was about 100 volts. Further experiments are in 

 progress. 



Amherst, Mass., May 24, 1912. 



*See Ann. der. Ph.ys., pp. 445-454, 1911, " Uber die aktinodielektrische 

 Wirkung bei den Erdalkaliphosphoren, naeh Versuehen von Eob. Oeder, 

 von C. Ramsauer und W. Hausser. 



