[ 64 ] 

 XIV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



Nov. 27, " T7XPERIMENTAL Researches in Electricity." By 

 1845. -C^ Michael Faraday Esq., D.C.L., F.R.S., &c. Nine- 

 teenth Series. Section 25 : On the Magnetization of Light, and the 

 Illumination of Magnetic Lines of Force. 



For a long time past the author had felt a strong persuasion, de- 

 rived from philosophical considerations, that among the several 

 powers of nature which in their various forms of operation on mat- 

 ter produce different classes of effects, there exists an intimate rela- 

 tion ; that they are connected by a common origin, have a reciprocal 

 dependence on one another, and are capable, under certain condi- 

 tions, of being converted the one into the other. Already have elec- 

 tricity and magnetism afforded evidence of this mutual convertibility ; 

 and in extending his views to a wider sphere, the author became con- 

 vinced that these powers must have relations with light also. Until 

 lately his endeavours to detect these relations were unsuccessful ; 

 but at length, on instituting a more searching interrogation of na- 

 ture, he arrived at the discovery recorded in the present paper, 

 namely, that a ray of light may be electrified and magnetized ; and 

 that lines of magnetic force may be rendered luminous. 



The fundamental experiment revealing this new and important 

 fact, which establishes a link of connexion between two great de- 

 partments of nature, is the following. A ray of light issuing from 

 an Argand lamp is first polarized in the horizontal plane by reflexion 

 from a glass mirror, and then made to pass, for a certain space, 

 through glass composed of silicated borate of lead, on its emergence 

 from which it is viewed through a Nichol's eye-piece, capable of re- 

 volving on a horizontal axis, so as to intercept the ray, or allow it 

 to be transmitted, alternately, in the different phases of its revolu- 

 tion. The glass through which the ray passes, and which the author 

 terms the dimagnetic, is placed between the two poles of a powerful 

 electro-magnet, arranged in such a position as that the line of mag- 

 netic forces resulting from their combined action shall coincide with, 

 or differ but little from the course of the ray in its passage through 

 the glass. It was then found that if the eye-piece had been so turned 

 as to render the ray invisible to the observer looking through the 

 eye-piece before the electric current had been established, it be- 

 comes visible whenever, by the completion of the circuit, the mag- 

 netic force is in operation ; but instantly becomes again invisible on 

 the cessation of that force by the interruption of the circuit. Fur- 

 ther investigation showed that the magnetic action causes the plane 

 of polarization of the polarized ray to rotate, for the ray is again 

 rendered visible by turning the eye-piece to a certain extent ; and 

 that the direction of the rotation impressed upon the ray, when the 

 magnetic influence is issuing from the south pole, and proceeding 

 in the same direction as the polarized ray, is right-handed, or si- 

 milar to that of the motion of the hands of a watch, as estimated by 

 an observer at the eye-piece. The direction in which the rotation 



