Michael Faraday, his Life and Works. 429 



markable ability, and thus arriving at results which he hardly 

 required experiment to confirm, so certain was he that this would 

 not contradict him. 



IV. 



I now pass to the last great series of Faraday's works. I 

 have said, and, I think, proved, that induction was the most 

 important of his discoveries; I must now say that the action of 

 magnetism and electricity upon light was the most brilliant. 

 Often the attempt had been made to see whether magnetism 

 and electricity exerted any direct influence upon light; but 

 these attempts had always failed. Investigators had operated 

 upon luminous rays travelling in the air or in liquids, and en- 

 deavoured to act upon them, sometimes by strong magnets, 

 sometimes by electric currents or by statical electricity; but 

 these attempts had led to nothing, absolutely nothing. All 

 these negative investigations have never been published, but they 

 have nevertheless been made. 



/ Guided by theoretical considerations upon the mutual cor- 

 relation of the forces of nature, Faraday, after many fruitless 

 attempts, succeeded in finding the connexion which exists be- 

 tween light and the magnetic and electric forces. Instead of 

 taking an ordinary ray, he operated with a polarized ray ; instead 

 of acting directly upon this ray by means of a magnet, he sub- 

 mits it to the influence of magnetism whilst it is traversing a 

 glass prism in the direction of its length. This prism, termi- 

 nated by two square and parallel bases, the surfaces of which are 

 well polished, and which are those by which the polarized ray 

 penetrates and issues from the prism, is placed between the poles 

 of an electromagnet in such a manner that its length and, con- 

 sequently, the direction of the transmitted ray are parallel to the 

 line joining the magnetic poles. Lastly, the polarized ray on 

 issuing from the glass prism only reaches the eye after passing 

 through a Nicolas prism which serves as an analyzer. It is also 

 by traversing a NicoFs prism before penetrating into the glass 

 prism that the ray of light is polarized; but this maybe effected 

 in any other manner. 



It is well known that by turning the analyzing prism to a 

 certain angle the polarized ray is extinguished, in such a manner 

 that the brilliant spot is replaced by a black spot. If, after this 

 operation has been effected, a strong electric current is passed 

 through the wire surrounding the electromagnet, the black spot 

 disappears and the bright one again makes its appearance. Then 

 by turning the analyzing prism a little further in the same di- 

 rection, the luminous ray is again extinguished, but this extinc- 

 tion ceases as soon as the magnetic action is suppressed by the 



