DECAY OF PHOSPHORESCENCE PRODUCED BY HEATING. 



IOI 



upward bending is possible; but a downward bending is impossible unless 

 both the bands subsequently decay together. This suggests that one of 

 the bands may be due to some secondary effect, instead of being produced 



20 40 60 80 100 120 140 



Seconds 

 Fig. 104. 



Effect of history previous to excitation. Excited 30 seconds. Before each excitation the powder wa3 

 excited for 10 minutes and allowed to decay to an intensity corresponding to IJ =9. at which time the 

 excitation of 30 seconds was begun. 



Curve C. excitation and decay at room temp. 



B, " 88 C. 



A. " 133 



8 10 



Minutes 



Fig. 105. 



Effect of varying the length of excitation. Excitation and decay at a temperature of 1S C. (replotted from 



data of Micheli). 

 Curve A, excited 5 seconds; B, 20 seconds; C, 300 seconds. Another curve excited for 60 seconds coin- 

 cided almost exactly with curve C. 



Fig. 106. 



Effect of varying the temperature at which excitation and decay take place. Excited 300 seconds 



(replotted from data of Micheli). 

 Curve A, temp, of excitation and decay, 21 C. 



B, " " ioo 



C, " " 18 



by the exciting light. Such a band would increase in intensity a certain 

 length of time, then decrease in intensity. If we suppose that the first 

 band follows the law suggested, and that the second band follows the same 



