186 ELLIPTIC POLARIZATION. 



bisects the supplement of the angle formed by their direc- 

 tions. 



This property enables us to distinguish a circularly-po- 

 larized ray from a ray of common light. On the other hand, 

 it is at once distinguished from plane-polarized light, by the 

 circumstance that it is divided into two rays of equal inten- 

 sity by a double-refracting crystal, whatever be the position 

 of the plane of the principal section. 



(197) The effects produced upon light by reflexion at the 

 surfaces of metals were first observed by Malus. 



Malus found that metals differed from transparent bodies, 

 in their action upon light, in this, that common light was 

 never completely polarized by reflexion at their surfaces. The 

 phenomenon of polarization was, however, partially produced; 

 and the effect increased to a maximum at a certain angle of 

 incidence. 



When the incident light was polarized in a plane inclined 

 at an angle of 45 to the plane of incidence, Malus observed 

 that the reflected light was completely depolarized, the pencil 

 being divided into two by a double-refracting prism in every 

 position of its principal section. 



(198) The subject of metallic reflexion was next studied 

 by Sir David Brewster, and the laws of the phenomena 

 investigated in much detail. These laws may be reduced to 

 the following : 



I. When a ray of common light is incident upon a me- 

 tallic reflector, the reflected light is partially polarized, the 

 amount of polarized light in the reflected pencil increasing 

 up to a certain incidence, which is thence called the angle of 

 maximum polarization. 



II. When the light is reflected several times in succes- 



