FAEADAY. 791 



change in the lines of the spectrum of a flame when the flame was acted on 

 by a powerful magnet. 



This long series of researches is an instance of his persistence. His energy 

 is shewn in the way in which he followed up his discovery in the single 

 instance in which he was successful. The first evidence which he obtained of 

 the rotation of the plane of polarization of light under the action of mag- 

 netism was on the 13th September, 1845, the transparent substance being his 

 own heavy glass. 



He began to work on August 30, 1845, on polarized light passing through 

 electrolytes. After three days he worked with common electricity, trying glass, 

 heavy optical glass, quartz, Iceland spar, all without effect, as on former trials. 

 On September 13 he worked with lines of magnetic force. Air, flint, glass, 

 rock-crystal, calcareous spar, were examined but without effect. 



" Heavy glass was experimented with. It gave no effects when the same magnetic poles or the 

 contrary poles were on opposite sides (as respects the course of the polarized ray), nor when the 

 same poles were on the same side either with the constant or intermitting current. But when con- 

 trary magnetic poles were on the same side there was an effect produced on the polarized ray, 

 and thus magnetic force and light were proved to have relations to each other. This fact will most 

 likely prove exceedingly fertile, and of great value in the investigation of the conditions of natural 

 force." 



He immediately goes on to examine other substances, but with "no effect," 

 and he ends by saying, "Have got enough for to-day." On September 18 he 

 "does an excellent day's work." During September he had four days of work, 

 and in October six, and on 6th November he sent in to the Royal Society the 

 19th series of his "Experimental Researches," in which the whole conditions 

 of the phenomena are fully specified. The negative rotation in ferromagnetic 

 media is the only fact of importance which remains to be discovered afterwards 

 (by Verdet in 1856). 



But his work for the year was not yet over. On November 3, a, new 

 horseshoe magnet came home, and Faraday immediately began to experiment 

 on the action in the polarized ray through gases, but with no effect. The 

 following day he repeated an experiment which had given no result on October 6. 

 A bar of heavy glass was suspended by silk between the poles of the new 

 magnet. "When it was arranged, and had come to rest, I found I could 

 affect it by the magnetic forces and give it position." By the 6th December 

 he had sent in to the Royal Society the 20th, and on 24th December the 

 21st series of his " Researches," in which the properties of diamagnetic bodies 



