io6 



STUDIES IN LUMINESCENCE. 



curves plotted with time measured from the beginning of heating. Here 

 again, if one considers the first flash alone, the curves are similar to those 

 shown in the ease of Sidot blende. The longer the delay in heating, the 

 less intense the flash and the later the maximum intensity of each flash. 

 Furthermore, the time of decay at one temperature and constant length 

 of excitation is constant. It is difficult to make any deduction from the 

 points representing the second flash. 



Another set of curves similar to those shown in Fig. 1 13 is shown in Fig. 

 115. These curves show that the second flash becomes relatively larger 

 with respect to the first as the excitation is shortened, and under suitable 

 conditions, as in curve C, may become considerably larger than the first. 



80 



120 /eo 



Fig. 114. 



Effect of delay in heating. Time measured from the beginning of heating 



ZOO 



2.40 



Same curves shown in Fig. 113. 



It is difficult to say how much difference exists between the behavior of 

 Sidot blende and Balmain's paint. The decay curves at room temperature 

 are very much alike. As the temperature is raised both decay curves 

 become straight lines, but Balmain's paint shows a transition through a 

 double curvature decay before reaching the straight line decay, while Sidot 

 blende does not exhibit this phenomenon. Above the temperature at 

 which the decay curve becomes straight, Balmain's paint shows a decay 

 approximating the decay at room temperature, while in the case of Sidot 

 blende the decay is too rapid to be followed with the available apparatus. 

 The decay of Sidot blende is so rapid that one can not get enough points 



