272 



NICHOLS— PHOSPHORESCENCE OF SULPHIDES. 



published a diagram which overlaps the range of the present experi- 

 ments. Three of his curves are for a Sr, Bi; Ca, Bi and Ba, Cu 

 sulphide respectively ; corresponding to and possibly identical with 

 our 13, 3 and 33. These show a linear process which he regards 

 as the first process in the decay and which, as he points out, has. 



Fig. 8. 



in each case, a much steeper slope than the first process, so called, 

 obtained by observations covering the range from a second or more 

 onwards. The slope of his lines considering the range from .01^ to 

 .03^ and remembering that Zeller did not determine the decay for 

 various regions of the spectrum separately are fairly comparable 

 with the second process (beyond the knee) in Figs. 6 and 7 if we 

 select the regions including the principal crest. We may therefore 

 regard Zeller's process which extends as far as .06 second as the 

 same as our second process. 



