688 Prof. G. V. Raman and Mr. K. Seshagiri Rao on 



where -\jr and yft' are- the ancles of incidence and refraction 

 at the surface of the plate. 



. Fig. 2. 



In fig. 2 (b) we have one ray undergoing a single 

 refraction at the surface of the meniscus and emerging 

 in f o the air, and the other ray passing wholly through 

 the liquid and totally reflected at the surface of the 

 meniscus. The path-difference in this case is 



— ~(oosr + cosr')~ fit sin -?-= \-^fit(cosi + cos i') — £ 



and 



sin 8 = sin? 5 ' = sin (yjr — r — i). 



