176 Dr. J. Kerr on Reflection of Polarized Light 



of magnetization, effects which are of the same kind as those 

 produced by rotation of the second Mcol, cannot be explained 

 by any mere changes of the primitive vibration in amplitude 

 or phase, or by any thing except the introduction of a new and 

 very small component in a direction perpendicular to the 

 primitive vibration. 



24. General Law of the Action of Magnetism upon the Re- 

 flected Ray. 



The three following assumptions appear to me to afford a 

 perfect explanation of all the principal phenomena. They 

 were suggested as above, and were tested by a careful mathe- 

 matical discussion of the results of all the experiments in suc- 

 cession. The discussion presents little difficulty, but is too 

 tedious to be offered here. 



(1) When the original vibration is parallel or perpendicular 

 to the plane of reflection, the effect of magnetization of the 

 mirror is to turn the vibration through a very small angle in a 

 direction contrary to the Amperean currents. 



The resolved parts of the vibration so turned, one in the 

 direction of the primitive vibration and the other perpendicular 

 to it, may be called the primitive component aod the new 

 component respectively, as in art. 23. 



(2) The primitive component is always reflected according 

 to the same laws of retardation of phase, after magnetization 

 of the reflector as before. 



(3) Whether the new component be parallel or perpendi- 

 cular to the plane of reflection, and whatever be the angle of 

 incidence, the phase-retardation of the new component (with 

 reference to a standard reflected ray, polarized in the plane of 

 incidence, and incident in the same phase as the actual primi- 

 tive), is always an angle in the first quadrant, and much nearer 



to zero than to ^. 



It will be admitted that the assumption (3) is a very re- 

 markable one, and very important if true. I hope to see this 

 geometric theory of the phenomena verified by the mathema- 

 ticians, or something better put in its place. 



25. It would be superfluous now to offer any explanation of 

 the absence of all optical effect of magnetization in the case 

 of normal incidence (art. 21). It is not so easy to understand 

 the absence of effect at incidences very near grazing, 85° to 

 90°, in the first four experiments. We might expect indeed, 

 on the contrary, that as the ray approaches parallelism to the 

 lines of force, or as the front of the wave approaches perpen- 

 dicularity, the magnetic force would act at a greater advan- 

 tage, and the optical effect would therefore become stronger. 



