188 ELLIPTIC POLARIZATION'. 



ray may be resolved into two, polarized respectively in the 

 plane of incidence and in the perpendicular plane ; and these 

 planes, by the third of the preceding laws, are unaltered by 

 reflexion. The two components, however, undergo changes 

 both of intensity and phase ; and when these are known, the 

 character of the reflected pencil is completely determined. 



This problem has been solved experimentally, by M. Ja- 

 min, in the most complete manner. 



(200) The intensity of the light reflected by a metal at 

 different incidences is determined by M. Jamin by comparison 

 with the intensity of light reflected from glass under the same 

 angle, which latter is known by Fresnel's formulas (184, 5 ). A 

 plate of metal, and one of glass, are placed in the same plane, 

 and in contact, and the light is allowed to fall partly upon 

 each. When the incident light is polarized in the plane of 

 incidence, the light reflected from the metal, as well as from 

 the glass, continues polarized in that plane. If, therefore, 

 the two reflected pencils be received on a double-refracting 

 prism, whose principal section coincides with the plane of 

 incidence, each of then\ will furnish a single refracted pencil. 

 But if the principal section of the prism be inclined to the 

 plane of incidence at any angle, a, each of the reflected 

 pencils will furnish two refracted pencils, whose intensities 

 will vary with the azimuth of the principal section according 

 to the known law of Malus. 



Let I be the intensity of the light reflected from the metal, 

 and I 7 that of the light reflected from the glass. The inten- 

 sities of the ordinary and extraordinary pencils, into which 

 the former is subdivided by the prism, are respectively 



I cos 2 a, I sin 2 a ; 



and those of the corresponding pencils, derived from the latter, 

 are 



I' COS 2 a, I' sin 2 a. 



