﻿common Light obliquely incident on parallel plates. 207 



1 1 1— k 2 1 1— v 2 



plates will be changed from o to o ' TTF' *' e ' to 2 * 1 -4- 3 2 J 



and the intensity of the beam reflected from two plates will be 

 1/ l-fi 1 2k 2 _1 4z; 2 

 2V 1 + /c7~ 2 ' 1 + A« ~ 2 ■ " 1 + 3i> 2 ' 

 Now let 



4p* __, 2 

 1+3** l ' 

 then 



1— v 2 



_i _ _ i __ z.2 . 



and the intensity of the beam which passes through two plates 

 will be i(l-AJ). 



Now consider the four plates of glass as two bundles, each 

 consisting of two plates. Then it will be seen that the intensi- 

 ties of the beams reflected and refracted by the two bundles will 

 bear the same relation to k\ that the intensities of the beams 

 reflected and refracted by the two plates bear to k 2 . Hence the 

 intensity of the light reflected by the two bundles is 



1 U\ _1 8v 2 



2 1+AJ 2 l + 7v 2 > 

 and the intensity of the light refracted through the two bundles 



is 



1 i-*;_i 1 



3 1 + AJ 2 l + 7v* 



Now let us consider the ray of intensity ^ which is polarized 

 in a plane perpendicular to the plane of incidence. It is clear 

 that the intensity of the beam arising at any surface from this 

 ray will bear the same relation to w 2 that the intensity of the 

 corresponding beam arising at the same surface from the other 

 ray bears to v 2 ; hence the intensity of the beam from this ray, 



-1 Q 2 



which is reflected from four plates, = - • - — — -^ and the inten- 



ii 2 

 sity of the refracted beam through four plates =-. 2 . 



Hence the whole intensity of the reflected beam is 

 /l Sv 2 1 Sw 2 \ 



and the whole intensity of the refracted beam is 



+ 



\ + 7v 2 ' 2 l+7w 2 



