its Circular Components in the Faraday "Effect" 475 



with less perfect definition than with the auxiliary prisms. 

 Also a single prism was used, the ray being sent in and out 

 once, and the aperture diaphragmed down to two narrow 

 openings, so as to resolve by the method of interferences, but 

 with no success. 



Of the two assumptions (acceleration of phase and of 

 velocity) upon which the above observed results may be 

 explained, the former does not appear to be tenable upon 

 dynamical grounds. Further, if there is a direct acceleration 

 in the rotation, it is difficult to see why a plane-polarized 

 vibration should be transmitted by its circular components to 

 explain the rotation of the vibration, rather than without 

 resolution and a direct rotation of the unresolved vector. 

 The latter assumption of a change in velocity must therefore 

 be adopted. 



It may also be remarked that, kinematically, it can be 

 shown that other modes of transmission may produce a 

 separation of the original system of rays into two opposite 

 circular systems. Gouy *, for example, has shown that a 

 rotary substance may produce a separation for a ray into two 

 circular components forming equal angles with their mean 

 position. His analysis involves essentially an integration, 

 over the refracting surface, of the elementary Huyghenian 

 zones, taking into account the continuous increase in orienta- 

 tion of the vector in the successive zones arising from the 

 varying thickness of the rotating medium. When the change 

 in orientation in absolute angular measure over unit width of 

 the stream is a very large quantity, the resultant reduces to 

 two opposite circular components referred to. This analysis 

 cannot apply to quartz or any other known natural rotary 

 substance, since in Fresnel's experiment this orientation was 

 not large compared with the width of the stream. In 

 magnetic rotary substances the same condition also holds, since 

 even in the case of iron the orientation is not a very great 

 quantity for finite angles. We must therefore conclude that 

 the resolution observed can only arise from the power of the 

 medium to transmit circular vibrations, only, in the direction 

 of the lines of force. 



Physical Laboratory, University of Nebraska, 

 JLin coin, January 5, 1901. 



Comptes Rendus, xc. p. 992 (1880). 



2 12 



