THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JUNE 1858. 



LII. On the Opiical Properties developed in Transjmrent Bodies 

 by the Action of Magnetism. By M. ViiRDET*. 



Part Illf. 



AFTER having determined the laws according to which tlie 

 optical properties developed by magnetism in transparent 

 bodies vary with the magnitude and direction of the magnetic 

 forces, I undertook to investigate how these pheenomena are 

 influenced by the nature of the transparent body. This I have 

 done by measuring the rotation of the plane of polarization, 

 effected by bodies of very different nature, when placed under 

 analogous circumstances, between the poles of an electro-mag- 

 net. Former labours of physicists have afforded me very scanty 

 information on this subject. Previous to my undertaking this 

 investigation, the only data which science possessed, consisted 

 in a small number of numerical determinations contained in the 

 memoirs of MM. Bertin, Edmond Becquerel and Wiedemann, 

 and in the much more numerous and varied experiments of 

 Prof. Faraday, which latter, however, were intended to show the 

 general nature of the phtenomena without attempting their mea- 

 surement. From so small a number of facts, it was impossible 

 todeduce any general law with certainty; and I shall show that, 

 in reality, those laws which have been sought to be established 

 arc inexact. 



In order to study the question, I have merely had to apj)ly 

 to a sufficient number of substances the methods which I dc- 



* Translated from tlic Annales de Chiinie et de Physique for February 

 1858, by Dr. V. Guthrie. 



t See the two former parts of this research, Ann. de Chim. et de Phys., 

 s. '.i. vol. .\li. p. '.iJ^K and vol. xliii. p. 'AJ ; the ])i-iiici[)al results contained 

 in these memoirs will be found abridf^ed in the iiiuth volume of the present 

 Beries of the I'hiloisophical Ma^.iziiie, j). -ISl. 



i'hil. May. S. 4. Vol. 15. No. 103. June 1858, 2 E 



