Propagation of Waves in a Resisted Fluid. 527 



if the rotation be from right to left, it is clear, from the pecu- 

 liar shape of the particle A, that there will be a greater resist- 

 ance offered to the motion of the aethereal fluid by the upper 

 portion {p) of the particle A than by the lower portion {q). 

 Consequently there will be a greater accumulation of resisted 

 aether on the side p than on the side q. On the contrary, it 

 is clear that, if the rotation be from left to right, the reverse 

 will be the case, and then there will be a greater accumulation 

 on the side q than on the side p. Now there are two resist- 

 ances acting upon each element of the aethereal fluid, as we 

 have already shown, one tangential opposing the motion of the 

 element along its circular path, the other normal^ opposing the 

 normal motion of deflexion of the element. In the present 

 case it is clear that the tangential resistance will be the same 

 whether we suppose the rotation to be from right to left or 

 from left to right, for in both cases the particle A is similarly 

 situated with respect to the direction of motion. But not so 

 with the normal resistance, for, the normal motion always 

 taking place from p towards q^ and the accumulation of re- 

 sisted fluid being greater on the sidejs when the rotation is 

 from right to left, and greater on the side q when the rotation 

 is from left to right, it is evident that the normal resistance 

 will be greater when the rotation is from right to left than 

 when it is in the opposite direction. Hence we may conclude, 

 in the case of a transparent substance whose particles are con- 

 stituted as is represented in fig. 2, that T will be the same 

 for right-handed and for left-handed circularly polarized light, 

 but that N will be greater for the former kind of light than 

 for the latter. 



In like manner, when the particles are constituted as is re- 

 presented in fig. 1, the same will be true, only N will be 

 greater for left-handed than for right-handed circularly po- 

 larized light. 



Now we have shown in article 11, that — must in general 



N 

 be very small compared with w H , and we may also con- 



N 

 elude that — is small compared with ??, except when the re- 

 sistance produces a very considerable effect upon the velocity 

 of propagation, which of course cannot be the case in sub- 

 stances of moderate refractive and dispersive power. Hence, 

 by the formula? (2.) in article (17.), we have very nearly 



AF = w (n -I j, 



