868 Profs. C. V. Raman and Bhabonath Banerji on 



often found, under the microscope, to possess an echelon- 

 like structure *. The stri?e diffract light asymmetrically 

 through large anodes, but the effects observed with different 

 striae differ in a manner which suggests thai the results are 

 influenced by the structure of the laminar edge as well as by 

 its total thickness. In the case of mixed plates, owing 

 to the action of surface tension, the laminar edges are not 

 perpendicular to the surface of the film, but have the form 

 of a meniscus (fig. 2). We shall assume that the angle of 

 contact of the liquid with the plate is zero, and that the 

 meniscus is of semicircular form. The diagram is assumed 

 to be drawn perpendicular to the plane of the film and also to 

 the element of the scattering boundary under consideration. 



Fi-. 2. 



It is obvious, especially in view of the curvature of the 

 surface of separation, that the incident light would be 

 scattered very differently towards the two sides of the 

 boundary between the two media. On either side, scattered 

 disturbances would emerge which have traversed different 

 paths partly through one medium and partly through the 

 other, and the problem is to find their relative intensities 

 and the path-differences under which they interfere. As 

 regards the light scattered towards the side of the more 

 refrangible medium, it is convenient to assume tentatively 

 that the paths traversed are those given by the laws of 



* P. N. Ghosh, " On some Phenomena of Laminar Diffraction 

 observed with Mica." Proc. Ind. Assoc, for the Cultivation of Science 

 Calcutta, vol. vi. pt. i. (1920). 



