ELLIPTIC POLARIZATION. 187 



sion, in the same plane and at the same angle, the proportion 

 of polarized light in the reflected pencil is increased ; and by 

 a sufficient number of reflexions the light becomes, as to 

 sense, wholly polarized in the plane of incidence. 



III. When a ray polarized in the plane of incidence, or 

 in the perpendicular plane, falls upon a metallic reflector, it 

 is polarized in the same plane after reflexion. 



IY. A ray polarized in any other plane is, in general, 

 partly depolarized by reflexion, the effect produced being 

 greatest at the angle of maximum polarization. * * "\ 



Y. When light, so depolaVized^uSd^rgoes a second re- 

 flexion in the same plane, and at the same angle, its polariza- 

 tion is restored. The new plane of polarization lies on the 

 opposite side of the plane of incidence from the original 

 plane, and its azimuth is changed. 



(199) From the last of the foregoing laws it is evident, 

 that the light produced by the reflexion of a polarized ray by 

 a metallic surface is not common light. Neither is it plane- 

 polarized light, since it does not vanish in any position of 

 the analyzing rhomb. It is eUipticatty-polarized ; and all the 

 phenomena are explicable on the hypothesis, that the two 

 oppositely polarized rays, into which the incident ray is re- 

 solved, differ in phase after reflexion, the difference amount- 

 ing to 90 at the angle of maximum polarization. For it 

 is plain that the effect of a second reflexion, in the same plane 

 and under the same angle, will be to double the difference 

 of phase, which thus becomes 180 ; and the resulting light 

 will be plane-polarized, the plane of polarization lying at the 

 opposite side of the plane of incidence. 



It is easy to see, from the foregoing, that the problem of 

 metallic reflexion is reduced to the determination of the inten- 

 sity, and the phase, of the reflected vibrations, in the case of 

 light polarized in the two principal planes. For any polarized 



