188 C. A. Butma/n — Effect of Phosphorescent Material. 



of readings is given below. The fatiguing effect due to I 

 voltages will be readily noted. The vacuum was -008 mm . 





Cms. 



per half uiin. 



Cms. per half inin. 





increasing field 



decreasing field 



Field 





to 600 



from 600 



— 0-35 











o-o 





1-0 



0-4 



+ 0-3 





5-1 





+ 2-0 





5-0 



2-0 



40-0 









5-4 



80-0 







c-o 



120-0 







6-5 



160-0 







6-5 



200-00 





7-6 



7-0 



400-00 





7-8 





600-00 





8-0 



.. 



Action of Different Parts of the Spectrum. 



Light through green, yellow, and red glass gave no photo- 

 electric effect and did not excite phosphorescence. The light 

 transmitted by these glasses was measured with a Hilger wave- 

 length spectrometer. From these data it was seen that the 

 photoelectric effect stopped at 4100 Ang. for CaBiNa. Sidot 

 Blende gave no effect with red glass and was not excited by 

 red, yellow or green light. The extreme red transmitted as 

 shown by the spectrometer was 7450 Ang. 



Experiments were made with infra-red light, but no effect 

 whatever could be obtained. Voltages from to ±600 volts 

 were used on the case. The infra-red light was obtained by 

 interposing a thin sheet of vulcanite between an open arc and 

 the quartz window of the chamber. 



Some experiments were made with light that had passed 

 through blue Uviol glass and the effect was obtained. If light 

 of all wave lengths from an open arc was used the deflection 

 was larger, but the effects were of the same character as 

 observed when the light was passed through glass. My ex- 

 periments were made through glass, thus eliminating the 

 problem of reflected light on the case. 



Discussion of Results. 

 In order to explain the phenomena observed, the hypothesis 

 may be made that the electrons set free get entangled in the 

 substance and build up fields in it. Fatigue would then be 

 due to this accumulated field building up. A strong field on 

 the case would overcome the field in the substance so that an 

 effect could be obtained. It must be remembered that these 

 phosphorescent substances are good insulators of the order of 

 quartz. Hence, this accumulated field is not neutralized when 

 the plate is earthed. Recovery would seem to be due to the 



