SPECTROPHOTOMETRY STUDY OF KATHODO-LUMINESCENCE. 139 



ments on Sidot blende (Fig. 148) the conditions as regards leakage were 

 more favorable and the current remained nearly constant. During the 

 observations corresponding to Fig. 148 the deflection of the galvanometer 

 varied from 32 for the highest voltmeter reading (33.8) to 37 for the lowest 

 voltmeter reading (11.7). In the experiments with willemite (Fig. 146) 

 the galvanometer deflection ranged from 7 to 25; and in the experiments 

 with cadmium sulphate the range was from 1 5 to 3 1 . 



The results obtained are plotted in Figs. 145 to 148 and are further 

 discussed below. 



CdSOi-\-xM nSOi. Tliis substance was prepared by C. W. Waggoner, who 

 has determined its decay curve when excited by the iron spark. 1 Excited by 

 kathode rays it gave an intense yellow fluorescence, with scarcely observable 

 phosphorescence. Close inspection of the powder showed occasional grains 



e* o 



Fig- 145- 



CdSO* +*MnS04. The curves to the left show the relation between discharge potential and intensity for 

 different wave-lengths. Curves / and // show the luminescence spectra for discharge potentials of 

 1 1,600 volts and 6,700 volts respectively. Curves /// and IV show, to a larger scale, the luminescence 

 spectra excited by ultra-violet light and Roentgen rays respectivelj'. 



which glowed with an orange or red light. At the end of our experiments, 

 after the powder had been bombarded by the kathode rays for about 10 

 hours, the surface was found to have acquired a ruddy brown discoloration. 

 Upon standing for several months the powder scarcely responded at all to 

 excitation by the iron spark, but recovered its activity after heating. 



Inspection of curves / and II, Fig. 145, shows that the form of the fluo- 

 rescence spectrum is independent of the discharge potential, and therefore 

 of the velocity of the kathode rays, since it is clear that one of these curves 

 might be obtained from the other merely by changing the scale. 



1 Waggoner, Physical Review, xxvir, p. 209, 1908. See also Chapter VII of this memoir. 



