266 NICHOLS— PHOSPHORESCENCE OF SULPHIDES. 



stant frequency interval, the approximate interval being 39. The 

 location of the members of this series which coincide with maxima 

 are indicated by vertical lines. Frequencies (i//xX 10^) and wave- 

 lengths are given in Table II. 



Here every member of the series is represented by a recognizable, 

 although in some cases somewhat indefinite maximum in the curve. 

 as far as .5300 /x. If we extend the series further towards the violet 

 we find that the ninth member beyond .5300 /x lies at .4468 /t (fre- 

 quency 2238) and this coincides with the main crest well within the 

 errors of observation. There are other barely discernible indications 

 of submerged crests on either side of the principal crest. 



The most striking example investigated in this preliminary study 

 is that presented by L. and K. No. 33, a barium sulphide with copper. 



Here we have obviously two overlapping complexes of bands 

 (see Fig. 5), at least 14 crests of which are indicated more or less 

 definitely by the irregularities in the spectrum curve. 



In this case the bands fall into two groups. From wave-length 

 .5 ft towards the violet the frequency intervals between neighboring 

 crests are all multiples of 70. Towards the red the interval is 26.6 

 for all but one band. This band at .5376 /x falls however into the 

 series having the constant interval of 70. 



To indicate the closeness of the agreement vertical lines have 

 been drawn on the diagram in Fig. 5, as in the previous cases, at 

 wave-lengths corresponding to those members of the two series of 

 constant interval which coincide with observable crests. Solid Hues 



