80 Mr. A. E. Tutton. A f 1 iiiiiji,-''fir,- 



These ratios may be simplified by referring them to ^ for KZn 

 selenate as unity, when the values for that salt become identical with 

 the axial ratios. These ratios are as under : 



Comparison of the Orientations of the Optical Indicatrix. 

 Inclinations of Axis a of Indicatrix to Vertical Axis c. 



Diff. 4 4 

 8 44 



For potassium zinc selenate 9 9 



rubidium 13 13 



caesium 21 57 



The rotation of the ellipsoid is clearly illustrated by fig. 2. 



Comparative Table of Refractive Indices. 



