THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. IX. FOURTH SERIES. 



I 



LXVIII. On the Optical Properties developed in Transparent 

 Bodies by the action of Magnet' ym. By M. Verdet. 



[With a Plate.] 



Part I .* 



PROPOSE in this first investigation to measure anew the 

 rotations of the plane of polarization which are observed 

 when the direction of the luminous ray is parallel to that of the 

 magnetic forces, and to examine the laws according to which 

 these rotations depend on the distance and on the force of the 

 magnetic centres which act on the transparent bodies. 



Various difficulties present themselves on commencing this 

 investigation. First, in the usual conditions of the experiments, 

 e. (j. when the transparent body to be examined is placed between 

 the branches of the electro-magnet of M. Ruhmkorff, the various 

 points of the body cannot be regarded as subject to equal mag- 

 netic influences. Consequently the optical properties developed 

 by magnetism ought to vary from one point to another, and ob- 

 servation can only exhibit the result of a number of unequal 

 actions. A body of finite dimensions cannot be compared to a 

 body of infinitely small dimensions, which is the reverse of what 

 takes place in ordinary optical researches ; hence the elementary 

 law of the phenomena, that is to say, the only law which it is 

 of consequence to determine, cannot be immediately deduced 

 from these observations. 



Secondly, the optical properties developed in an elementary 

 slice of the transparent substance depend themselves on a very 

 complex combination of circumstances. The electro-magnet is, 

 in fact, a system of magnetic centres whose distribution is not 

 exactly known ; the properties acquired by an elementary plate 

 of the substance depend evidently on the distance of these centres, 



* Abridged from the Annates de Chimie ct tie Physique, 3rd series, vol. xli. 

 Phil. Mag. S. 4. No. G2. Suppl. Vol. 9. 2 1 



