268 



NICHOLS— PHOSPHORESCENCE OF SULPHIDES. 



estimates of the wave-lengths would seem to be significant. The 

 curves however were plotted directly from the spectrophotometric 

 readings without reference to any possibly symmetrical arrangement 

 of the crests. 



TABLE in. 



Approximate Frequencies and Wave-Lengths of Visible Crests in the 

 Spectrum of the Phosphorescent Sulphide L. and K. No. 33. 



Wave-Lengths. 



4255 

 4386 



4673 

 4831 



5000 

 5376 



Visible crests zvith interval z= 70. 



Frequencies i/A X lo'. 

 2350 

 2280 



2140 

 2070 

 2000 



i860 



Intervals. 

 70 



70X2 



70 



70 



70X2 



Visible crests ztnth intervals 26.6. 



Wave-Lengths. Frequencies. Intervals. 



5000 ^ 2000.0 26.6 X 2 



5 136 1946.8 26.6 X 2 



5283 1892.6 26.6 X 7 



5861 1706.4 -^ 26.6 X 2 



6049 1653.2 26.6 X 2 



6250 1600.0 26.6 X 2 



6465 1546.8 



6578 1520.2 26.6 



669s 1493-6 26.6 



Whether the spectra under consideration are to be regarded as 

 consisting of a single band or of more than one band is not a cjues- 

 tion of complexity of structure. Any system, however complex, 

 which behaves as a unit under varying conditions of temperature, 

 mode of excitation, etc., all the components being afifected in like 

 manner, may be considered as a single band in the sense in which 

 that term has been used by Lenard. We have a striking example 



