﻿Polarization of Light obliquely incident on parallel plates, 205 



while engaged in other investigations, cannot well be explained 

 otherwise than by the assumption of such an asymmetrical 

 widening of one or the other of the two sodium-lines. 



He has found that the Newton's interference-bands which, 

 with a difference of path of about 20,000 undulations, are pro- 

 duced in a piano-parallel glass plate of 5 millims. thickness by 

 homogeneous light from sodium, are displaced almost the whole 

 distance of two rings when the intensity of the sodium-flame is 

 varied, in the manner above indicated, by alteration of the 

 amount of vapour. With this displacement is connected a si- 

 multaneous diminution of the sharpness of the rings as the in- 

 tensity increases, until they completely vanish, this being a 

 necessary consequence of that diminution of the homogeneity of 

 the light which is expressed in the widening of the lines. The 

 magnitude and direction of this displacement points to a diminution 

 of the refrangibility of the light , to which in the spectrum a dis- 

 placement of one or the other sodium-line of at most ^oo-iw °f 

 their reciprocal distance would correspond. 



Hence it is evident that this method of observation is vastly 

 more delicate for the indication of asymmetry in the widening 

 of the lines than the spectroscopic one, as long as its application 

 is not prevented by the want of sufficient light. 



Fuller details on these experiments will be communicated by 

 Dr. Muller in a special memoir which will shortly be published ; 

 and I intend to treat the theorems developed in the foregoing in 

 their application to the investigation by spectrum-analysis of the 

 physical constitution of the heavenly bodies, and particularly to 

 the determination of the conditions of temperature and pressure 

 of the solar atmosphere. 



XXVII. To determine the degree of Polarization in the case of a 

 ray of common Light falling obliquely on and being reflected or 

 refracted by a bundle of parallel Plates. By W. G. Adams, 

 Professor of Natural Philosophy in King's College*. 



REGARDING a ray of common light as equivalent to two 

 polarized rays of equal intensity, whose planes of polari- 

 zation are in and perpendicular to the plane of incidence, then 

 a ray, of intensity I, is equivalent to two, each equal to J. 



The ray of intensity \ which is polarized in the plane of inci- 

 dence will give rise to a reflected ray of intensity ^v % } and a re- 

 fracted ray of intensity J(l — v*), where v denotes the ratio of 

 the amplitudes of the vibrations of the ether for the reflected 

 and the incident ray. 



If <j> and (j) t be the angles of incidence and refraction on the 

 * Communicated by the Author. 



