136 C. A. Batman — Effect of Phosphorescent Material. 



Ca,Bi,Na. The vacuum varied between -0007 and -002 mra . 

 The sensitiveness of the electrometer during this test was 

 between 1600-1700""" per volt. The accelerating field used 

 was 2 volts. Curves I and II were run with a wait of two and 

 one-half minutes with light off between readings. The elec- 

 trometer was grounded and allowed to return to zero during 

 the wait. Curve III is a set of continuous readings. 



Another important feature is the recovery from fatigue dur- 

 ing the night. The recovery is less on successive days. 



Fig. 2. 



|0 12 



20 22 ZH 



Between I and II no field was on the case during the night. 

 Between II and III a voltage of two volts was on the case. 



Experiments were made to see what effect the thickness of 

 the layer had on the photoelectric fatigue. No matter how 

 thick or thin the layer was, fatigue and recovery were always 

 present. A moderately thick layer was measured and found to 

 be , 06 mm . The thinnest layer examined consisted of discrete 

 particles with large distances between them. 



A series of experiments were performed to find out the in- 

 fluence of voltage on fatigue. With positive 600 volts on the 

 case the fatigue was found faster than with two volts. It was 

 found, for instance, that a constant value of deflection could be 

 obtained for two volts. ~Now if higher voltages up to 600 

 volts were put on the case and a series of readings taken, it was 

 always found that the reading with two volts was much less 

 than it had been before and in some cases no deflection at all 

 could be obtained. If now the maximum voltage of 600 volts 

 was put on the case approximately the same value as before 

 was obtained. 



