DCAY OF PHOSPHORESCENCE PRODUCED BY HEATING. 



8 9 



released to give the flash peculiar to thermo-lumineseence. If this is the 

 case, the areas between the curves in either Fig. 80, 81, or 82 and the coor- 

 dinate axes should be equal to each other. It is impossible to get experi- 

 mental data with which to draw the curves to the axis, so the author pro- 

 jected the curves tentatively. This is not an entirely rash thing to do, 



Fig. 81. 



Curves similar to those in Fig. 81. Excited 80 seconds at room temperature. Curve A, heated to 

 308 C; curve B, heated to 267 C; curve C, heated to 206 C; curve D, heated to 155.5 C; 

 curve E. heated to 99 C. 



because a slight variation in the prolongations will have effect; furthermore, 

 while the low intensities were not measurable, one could nevertheless get 



Fig. 82. 



Curves similar to those in Figs. 80 and 81. Excited 320 seconds at room temperature. Curve A, 

 heated to 309 C; curve B, heated to 266 C; curve C, heated to 207 C; curve D, heated to 

 153 C; curve F, heated to 98 C 



some idea of the rapidity of decay by noticing how rapidly the photometer 

 screen became dark. 



Fig. 83 shows the areas plotted with temperatures as abscissas. 



If the areas had been equal to each other for a given excitation, each of 

 the curves in Fig. 83 would have been a straight line parallel to the tempera- 

 ture axis. Aside from the low values at 300 , which are probably due to 



