NICHOLS— PHOSPHORESCENCE OF SULPHIDES. 



267 



belong to the group with an interval 70, dotted lines to the 26.6 

 interval. Wave-lengths, reciprocals and intervals are given in 

 Table III. 



The designation of these series as of constant interval, upon the 

 basis of the curves in Figs. 3, 4 and 5, can be tentative and approxi- 



FiG. 5. 



mate only ; but no systematic departure large enough to be detected 

 appears to exist. The wave-lengths given in the tables are those of 

 the vertical lines and therefore of the members of the constant inter- 

 val series which coincide with the various crests. No independent 



