Magneto-optic Phenomenon. 295 



always retardations, reckoned with reference to the reflected 

 wave polarized parallel to the plane of incidence. 



In accordance with the convention adopted by all previous 

 observers, I have called the magnetization positive if the 

 north poles of the magnetic molecules are directed towards 

 that side of the normal to the mirror on which the polarizer 

 lies. 



3. We can now deduce the formulae which serve to de- 

 termine the amplitude fju and the phase m of the magnetic 

 component of the light, in the case of a bundle of incident 

 rays polarized parallel to the plane of incidence. In these 

 formulae / and h are the amplitudes of the reflected light 

 polarized parallel and perpendicularly to the plane of incidence 

 respectively, when the incident ray has amplitude equal to 

 unity and is polarized in the same plane. <I> is the relative 

 difference of phase of these two waves in the case of metallic 

 reflexion. 



Let the polarizer be set parallel to the plane of incidence ; 

 and let the amplitude of the light incident on the mirror be 

 unity. Now turn the polarizer through a small angle, <j>. . 

 The rays falling on the mirror are then: — 



A ray polarized parallel to the plane of incidence, ampli- 

 tude 1 ; 



A ray polarized perpendicularly to the plane of incidence, 

 amplitude <f>. . 



By reflexion, we obtain : — 



A ray polarized parallel to the plane of incidence, ampli- 

 tude f, retardation of phase zero ; 



A ray polarized perpendicularly to the plane of incidence, 

 amplitude h<f>. , retardation of phase <I> ; and 



A ray polarized perpendicularly to the plane of incidence, 

 amplitude ^., retardation of phase m*. 



If now the analyser be turned through a small angle </). 

 out of the position in which the reflected light was quenched 

 before the polarizer was turned and the mirror magnetized, the 

 analyser transmits a bundle of rays with 



amplitude —f<j> ia , retardation of phase 0, 



» Hip} v « $, 



* The indices attached to fx and m indicate that the plane of polarization 

 of the incident ray is nearly parallel (*) or nearly perpendicular (/) to the 

 plane of incidence. 



Y2 



