420 H. S. Uhler — Deviation Produced oy Prisms. 



In order to plot quantities which are measured in terms of 

 the same unit, the critical angle instead of the index of refrac- 

 tion is taken as ordinate with the prism angle as abscissa. For 

 practical convenience a few arbitrary values of the index of 



Fig. 8. 



refraction are indicated on the line parallel to the axis of ordi- 

 nates. As the critical angle increases from to -Jtt the index 

 of refraction decreases from oo to 1. In order to avoid total 

 reflection the condition /3 <" 2<? must be fulfilled. Hence, for 



