applying to Light under the action of Magnetism. 471 



tally towards the right as regards the course of the light in 

 the first experiment, ?/ 2 towards the right as regards the course 

 of the light in the second experiment (or opposite toj/,); % 

 vertical, in a direction common to both experiments. Then, 

 for the first experiment, in order to represent the displace- 

 ment of particles constituting that ray of circularly polarized 

 light, in which every particle describes a circle in the direc- 

 tion, viewed from the origin of light, opposite to that of the 

 hands of a watch, and in which at any one time the position 

 of all the particles, originally in a straight line, has become a 

 right-handed helix (which I will call Ray No. I.) ; we must 

 take the following expressions : — where t is the period of vi- 

 bration, t/j the velocity of transmission of the wave, and Y'j 

 and Z' the displacements in the direction of y l and z re- 

 spectively, 





Similarly, to represent, for the first experiment, the displace- 

 ment of particles constituting the ray circularly polarized in 

 the opposite direction, or so that each particle describes a 

 circle in the same direction, viewed from the origin of light, 

 as the hands of a watch (which I shall call Ray No. II.), we 

 must have 



Y^.co^-i), 

 Z» 1= -*.si„i^-i)). 



And in the second experiment, to represent the Ray No. I. 

 of that experiment, we must combine 



Z< 2 = a.sin^(,_£j) ; 

 and to represent the Ray No. II., we must combine 



And the thing which it is very important to observe is, that 



