THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



MAT 1877. 



XL III. On Hotation of the Plane of Polarization by Reflection 

 from the Pole of a Magnet. By John Kerr, LL.D. y 

 Mathematical Lecturer of the Free Church Training College, 

 Glasgow** 



1. WAS led some time ago to think it very likely, that if 

 -*- a beam of plane-polarized light were reflected under 

 proper conditions from the surface of intensely magnetized 

 iron, it would have its plane of polarization turned through a 

 sensible angle in the process or fact of reflection. The known 

 facts upon which this expectation was founded are indicated 

 briefly under the five following heads. 



(1) The effects discovered by Faraday in his famous polari- 

 scopic experiments in the magnetic field, 



(2) Many instances in optics to this effect — that a reflected 

 vibration may have its character determined wholly or partly 

 by the refractive power of the reflector, or, more generally, by 

 the specific properties of the reflecting body in relation to 

 transmitted light. I may adduce Brewster's law of the polari- 

 zing angle, also Fresnel's theory of reflection from glass &c, 

 a theory which is still accepted and applied in delicate photo- 

 metric work as affording a good expression of facts, and which 

 treats refraction and reflection as closely related parts of one 

 dynamic whole. I may adduce also the laws of reflection from 

 the surfaces of Iceland spar and other birefringent bodies. It 

 is true that in this last case the catoptric effects are extremely 

 faint in comparison with the dioptric — a fact which is clearly 

 unfavourable to the proposed case of reflection from iron, as 

 contrasted with the resolved cases of transmission through 



* Communicated by the Author. 

 Phil Mag. S. 5. Vol. 3. No. 19. May 1877. Y 



