of Reflexion of Polarised Light, 



509 



IS 



reflected light moves 

 as in the annexed 

 figure. Let POA be 

 the azimuth of inci- 

 dent light, and POA 

 equal to GO A; PO 

 is the position of the 

 axis major corre- 

 sponding to 0° in- 

 cidence ; A the po- 

 sition of the axis 

 major in the plane 

 of incidence corre- 

 sponding to the prin- 

 cipal incidence ; and 

 OG the position of the axis corresponding to 90° incidence. 



Law VI. That when the azimuth of the incident light 

 greater than the cir- 

 cular limit, the axis 

 major of the reflected 

 light moves as in the 

 annexed figure. Let 

 POA be the azimuth 

 of the incident light, 

 and GOB equal to 

 POB. 



At the incidence 0"^ 

 OP is the position of axis major; as the incidence increases 

 from 0° to the principal incidence, the axis major moves from 

 OP to 0.2? and turns back, attaining the position OB at the 

 principal incidence ; and as the incident angle increases from the 

 principal incidence to 90°, the axis major moves from OB to 

 Oy and back again to OG. 



Previous to entering upon a description of the experiments by 

 which the foregoing six laws are proved, it will be useful to show 

 by an example the manner in which the received laws of Fresnel 

 and Arago deviate from the observed facts. 



According to Fresnel, if a unit of light be polarized in the 

 plane of incidence and reflected from an uncrystaliine transparent 

 body, the intensity of the reflected beam will be measured by the 

 square of the fraction 



sin (i-r) 



[i + rY ^'^ 



Plane of 



incidence. 



1 = 



sm 



i and r being the angles of incidence and refraction. If the unit 

 of light be polarized in a {)lane perpendicular to the plane of in- 



