of the double refraction in strained glass. 



331 



Fig. 6. Glass S 57. 



A-5400X . 1375 A-5400y 



c 



\-5400\ ..__ /X -6400V 



ooo~j-' 1438 (^ooo-) 



iUfln \ /X-iUOOV 



c = - 1 .o 9 3 + . 3 4S 8 (^)- 1 4a 8 (^5y 



-1-40 



450u 



Wave-lengths in tenth-metres. 



good 



x Ohservations A 



+ 



o 



No observations could be taken of the glass O 198 as the 

 highest pressure which could be attained by means of the instru- 

 ment, namely about 250 kilogrammes weight per sq. cm., was 

 insufficient to reach the first extinction in this glass. 



9. The results are exhibited graphically in Figs. 1—6. 

 In calculating the constants of the curves to fit the observations 

 the mean wave-length X 5400 has been taken as a convenient 

 origin. 



22—2 



