from the Equatorial Surface of a Magnet. Ill 



But against this we have what appears to be fairly established 

 by observation as a general truth in optics, that the specific 

 differences of reflectors become less and less marked as inci- 

 dence approaches grazing, until at grazing they almost en- 

 tirely disappear. 



26. I shall not make any lengthened comparison between 

 the effects now observed in connexion with the equatorial sur- 

 face and those formerly obtained in the case of the polar sur- 

 face. The two sets of results are not inconsistent, nor do they 

 differ materially in any way, except that the present set con- 

 tains a larger amount of detail as to the variations of optical 

 effect, variations extending even to reversal. I have no doubt 

 that this enlargement of results is due to better means and 

 improved arrangements in the present series of experiments. 

 It will be remembered that a submagnet, separated from the 

 mirror by a very narrow chink, was found indispensable in 

 the case of the polar surface. In the present experiments 

 there is no place for such an adjunct, and the reflector is fully 

 exposed to view at all incidences, which is a great improve- 

 ment. The new arrangements are also simpler and more ma- 

 nageable upon the whole, and much better adapted for delicate 

 and exact optical observation. 



In one respect I have certainly found the polar surface 

 superior to the equatorial. In the case of the polar surface, 

 and with the power that I have applied, it is easy to obtain, by 

 magnetic force alone, a very distinct restoration of the reflected 

 light from pure extinction, though the restoration is never 

 very strong ; but in the case of the equatorial surface, and 

 with equal or greater powers, I have never seen any stronger 

 effect of unassisted magnetic force than those fine movements 

 of the band in the fifth and sixth experiments. 



27. The first facts of magneto-optics discovered long ago 

 by Faraday, their more immediate consequences discovered 

 afterwards by Verdet and others — these and the additional 

 facts now published by myself must be all included ultimately 

 under one physical theory. It is very probable that the 

 remarkable theory of magnetism which has been advanced by 

 Sir William Thomson in a discussion of the former class of 

 facts, will apply as well to the latter. Probably also the theory 

 itself may receive additional confirmation in the process. I 

 think it equally probable that the new facts will find important 

 applications in the mechanical parts of the Wave Theory. But 

 in any event there is a new physical action secured thoroughly 

 to science, a specific action of magnetized iron upon light in- 

 cident at any point of its surface. 



Glasgow, January 21, 1878. 



Phil. Mag. S. 5. Vol. 5. No. 30. March 1878. N 



