NICHOLS— PHOSPHORESCENCE OF SULPHIDES. 



265 



complex band, or overlapping group of bands which merge into the 

 brilliant blue band at their more refrangible end. 



This is in agreement with the fact recorded in a recent paper^^ 

 that when this substance is excited to phosphorescence at the temper- 



.4^ -V^ "V' 



Fig. 4. 



ature of liquid air its color is blue-green instead of blue-violet on 

 account of the suppression of the band of shorter wave-length which 

 is dominant at ordinary temperatures. 



The crests shown in the curve BB also belong to a series of con- 



1^ Nichols, Proc. of the American Philos. Society, Vol. LV., p. 496, 1916. 



