264 NICHOLS— PHOSPHORESCENCE OF SULPHIDES. 



The agreement is sufficiently good throughout to warrant the 

 statement that : 



The hand consists of a complex the overlapping components of 

 which, so far as visible, are members of a series having a constant 

 interval. 



The following table gives the appproximate frequencies and 



wave-lengths. 



TABLE L 



Approximate Frequencies and Wave-Lengths of Visible Crests in Spec- 

 trum OF THE Phosphorescent Sulphide L. and K. No. 13 (Sr. Bi, NaoSOi). 



Visible Crests. Series. 



.4430 2257 



•4547 2199 



.4670 2141 



.4801 2083 



.4938 2025 



1967 



.5238 1909 



1851 



•5562 1793 



1735 



.5921 1677 



The three members of the above series not designated in the table 

 as corresponding to visible crests have wave-lengths at .5084 /a, 

 .5402 ju, and .5764 /x and these fall upon less definite maxima on the 

 curve than those which have been called visible crests. 



Another substance investigated with the spectroscope was a cal- 

 cium sulphide with bismuth as the active metal (L. and K. No. 3) 

 which is notable for its intense blue phosphorescence. 



The spectrum, as will be seen from Fig. 4, appears as a single 

 crested band with a well-defined maximum of unusual brightness 

 at about 447/*. It is of the well-known typical form, steeper 

 towards the violet and shows no visible evidence of complexity ; but 

 the phosphorescent light extends throughout the visible spectrum 

 although of relatively very small intensity in the longer wave- 

 lengths. Plotted to this scale no details of this weaker region can 

 be seen but if the ordinates be increased one hundred fold, as in 

 curve BB, various maxima and minima appear ; indicating a second 



