P. Eskola — Silicates of Strontium and Barium. 361 



Figs. 13 and 14 are diagrams of the variations in the 

 refractive indices of glasses of the systems SrO Si0 2 and 

 BaO-Si0 2 showing also the dispersions. 



Fig. 15. 



BaO 



SrO 



1.800 



1.750 



1.700 



1.650 



1.600 



.5 50 



1.500 



1.450 



too 

 Si0 2 



Fig. 15. — Variation of the index of refraction in strontium and barium 

 silicate glasses. 



Fig. 15 represents the same for the sodinm light. The 

 curves are drawn as far as the point corresponding to the 

 index of refraction of silica glass and extrapolated up to 

 the points of the hypothetical refractive indices of 

 barium and strontium oxide glasses. In this part the 

 curves, of course, can not give the values of the indices 



