Differential Double Refraction. 545 



Fig. 4. 



OrfCH/VATES FOR, SELEN/TF AND QUARTZ 



'00 90 80 70 60 50 40 30 ^0 10 10 20 50 40 



Y 





















S 









\ 





























\ 



Y 



\ 

























\ 



\ 



\ 



























Y 



\ 



























\ 



\ 



o 



























\ 



\ 





























Y 





\\ 



S. rs 























\ 



^ 



# 



Y^ 

























^ 



1 N 





























\ 





k\ 



























\l 



Y \ 





























\ x 



^\ 





























^ 



k 





























^ 



^s 































A/A 

























































\ 



\ 



s. 



























\ 



^ 



X 























% 





\ 



^ 



30 67 24 21 18 15 12 3 6 3 J 6 9 12 

 ORD/NATES FOR ICELAND SPAR A/VD M/Cfl 



