﻿common Light obliquely incident on parallel plates. 209 



and generally 



l + (2m-l)v*-2mf={l + (2m--l)w*\.cos*((j>-<l> 1 ). 

 Hence 



p _ 4sin 2 (j> — (ft t ) _ 4 



sin 2 ^-^) sin 2 (</> + </>,) 

 or 



£ = 4y 2 __ 4 tan 8 (ft — ft J 



w""l + 7v 2 -8y 2 "~ l + 7w 2 



4 



tan 2 (ft -ft!) tan 8 (ft -f ft,) 



It appears, then, for a single refraction at a single surface, 

 that 



■|(p« -i<;«) _ sin^ft-ft,) 



JKl-^+Kl-w 2 ) ~ 1 4- cos 2 (ft-ft^ 



or the degree of polarized light in the refracted ray depends 

 only on the deviation. 

 Now 



sinft—^sinft,; 



and from this equation we must determine the values of 



sin 8 (0-0Q 



sin 2 (ft + ftj) 



for different values of ft, from which we shall have 



p _ 4 sin 2 (ft - ^ftO . 



sm 2 (ft + ft,) 

 or 



1 7 



+ 



sin 2 (ft — ft,) and . 



w +^ _ sin 2 (6— ft,) sin 2 (ft + ft t ) 

 p 4 



Now suppose that before falling on the plate the light is po- 

 larized in the plane of incidence, and that p represents the part 



n 



P+ 2 . 

 polarized and n the natural light, then is the intensity of 



the first ray, and ^ - the intensity of the second ray ; hence 



Phil Mag. S. 4. Vol. 41. No. 272. March 1871. P 



