﻿49(5 Mr. C. V. Raman on Unsymmetrical 



side of the pattern. There can be one or two or [[more, the 

 number being the greatest integer in 



a(l — cos 0) 

 X ' 



This fact can be put in another way. If AB be the : face 

 or the prism and BP the incident wave-front, the limit to the 



Fio-. 2. 



A B 



G 



diffraction-pattern is set by the direction BA, for points on 

 the surface AB obviously cannot send out wavelets in the 

 direction AG. 



Measurements were made on the diffraction-pattern by 

 means of a micrometer, in order to test the theory. The 

 measurements given below were made at an incidence where 

 the asymmetry was not very marked yet sufficient to be 

 easily seen. 



a = 4-57 cms. A,= 6500 A.TJ. 6 = 1° 24' 55". 



Angular Distance from Observed. Calculated. 



The 5th minimum to the 4th 110" 108" 



4th „ to the 3rd 105" 110" 



3rd „ to the 2nd Ill" 113" 



2nd „ to the 1st 118" 115" 



1st minimum on one side to the 1st ] 

 on 



1st „ to the 2nd 125" 123" 



2ud „ to the 3rd 127" 126" 



3rd „ to the 4th 132" 130" 



4th „ to the 5th 132" 134" 



For the same -angle of incidence and with approximately 

 homogeneous light of mean wave-length 7100, the observed 

 width of the central band was 261" 4- 2", the calculated 

 value being 260 ;/ . Theory and observation agree as to the 

 number of bands on one side of the pattern, if it is not more 

 than six or seven. 



The facts described above suggest that by holding a fairly 

 wide rectangular aperture very obliquely in the pencil of 

 light, we should get an identical system of diffraction-fringes. 



the other j M ~ 6i 



