ELLIPTIC POLARIZATIOX. 189 



Hence, if the prism be turned, until the ordinary image of 

 the light reflected from the metal is equal, in intensity, to 

 the extraordinary image of the light reflected from the glass, 

 I cos 2 a = I x sin 2 a, and 



The azimuth of the principal section, a, is measured by means 

 of a graduated circle attached to the prism ; and the value 

 of I 7 for each incidence is given by Fresnel's formulas. 



A second measure is obtained, by turning the prism until 

 the extraordinary image of the light reflected from the metal 

 is equal to the ordinary image of the light reflected from the 

 glass ; and similar processes are followed in the case of light 

 polarized in the perpendicular plane. 



The results of these observations prove, that when light 

 polarized in the plane of incidence is reflected by a metal, 

 the intensity of the reflected light increases continually, as 

 the incidence increases from to 90, the total variation, 

 however, being very small. In the case of light polarized 

 perpendicularly to the plane of incidence, on the other hand, 

 the intensity of the reflected light diminishes from a perpen- 

 dicular incidence, up to the angle of maximum polarization, 

 and afterwards increases. The values found by experiment 

 accord satisfactorily with the results of M. Cauchy's dynamical 

 theory. The intensities of the reflected light, in the two 

 oases, are equal at the extreme incidences : at all other in- 

 cidences the intensity of the reflected light is less in the case 

 of light polarized perpendicularly to the plane of incidence ; 

 and the inequality is greatest at the angle of maximum 

 polarization. 



(201) It remained to determine the difference of phase of 

 the two component pencils corresponding to any incidence. 

 For this purpose two mirrors of the same metal were 



