LONDON, iM^^^k and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



SEPTEMBER 1846. 



XXVII. On the Magnetic Affection of Light, and on the Di- 

 stinction between the Ferromagnetic and Diamagnetic Con- 

 ditions of Matter. By Michael Faraday, F.R.S., Foreign 

 Associate of the Academy of Sciences, fyc* 



WHEN a ray of polarized light and lines of magnetic 

 force pass simultaneously and parallel to each other 

 through a transparent solid or liquid medium not possessing 

 forces of double refraction, the ray is rotated according to a 

 simple law of action, which I have expressed in the last part 

 of the Philosophical Transactions f. When such a ray passes 

 through certain specimens of rock crystal, oil of turpentine, 

 &c, it is also rotated according to a natural law well-known, 

 without any reference to magnetic force. A very striking di- 

 stinction exists between these two cases of rotation, though 

 they at first appear to be the same ; for the former rotation 

 is dependent in its direction upon the lines of magnetic force, 

 and not upon the position of the observer or the course of the 

 ray of light, whereas the latter is dependent upon the position 

 of the observer or the course of the ray. 



Upon consideration it appeared that the peculiar character 

 of the magnetic rotation might be made available in exalting 

 the final effect of the magnetic force upon the ray, and also in 

 demonstrating many important points in a more marked man- 

 ner and higher degree than had yet been possible ; and upon 

 referring the idea to experiment, it was found to be true. 

 The following pages contain some of the results. 



A parallelopiped of heavy glass 0"7 of an inch square and 

 2*5 inches long, had the two ends polished and silvered. The 

 silvering was then removed from a space about 0*1 of an inch 

 wide along one of the edges of one end, and also from a corre- 



* Communicated by the Author. 



f 1846, part i. pp. 4, 5. [Phil. Mag. vol. xxviii. pp. 298, 299.] 

 Phil Mag. S. 3. Vol. 29. No. 193. Sept. 1846. M 



