Transparent Bodies by the Action of Magnetism. 415 



had been thought to follow from the observations of MM. Bertin 

 and Edmond Beequerel. 



In his Traite tie l' Electridte, M. De la Rive, after having de- 

 scribed the principal experiments bearing on the magnetic rota- 

 tions of the plane of polarization, and having developed certain 

 theoretical ideas, makes use of the followiag words* : — 



" Thus the magnetic force only acts upon the sether by the 

 intervention of particles, and when the sether has a certain den- 

 sity due to the action exerted upon it by the particles between 

 which it is placed ; the magnetic action being more intense ac- 

 cording as the density of the sether is greater. Now, inasmuch 

 as the density of the fether does not depend exclusively upon that 

 of the body, that is, upon the approximation of the particles com- 

 posing it, but also upon the nature of these particles, it follows 

 that it is not always the denser body which is the most refraug- 

 ent, and which therefore shows the greatest magneto-rotary 

 polarization. Experiment completely confirms this view ; and on 

 glancing at the Table (still very incomplete) of the coefficients of 

 magnetic polarization, we are struck with the fact that the sub- 

 stances in this Table follow almost the same order as in the Table 

 of theii' refractive powers. New investigations are requisite to 

 establish fully the analogy which I have just pointed out, and 

 especially to determine the nature of the modifications which the 

 sether experiences under the influence of magnetism." 



This remark of M. De la Rive attracted my notice during my 

 former researches, as being worthy of a more attentive investi- 

 gation. The simplicity of the laws governing the magneto- 

 rotary powers inclined me, for a while, to the opinion which refers 

 these phajnomena to the direct action of the magnetic forces 

 upon the sether rather than upon the ponderable matter present, 

 and I therefore thought it highly probable that a relation might 

 exist between the magneto-rotary power and the refractive index, 

 which latter, as we know, may be taken as a measm-e of the 

 square root of the density of the sether. It will be seen imme- 

 diately that my conjecture has not been confirmed by experiment. 



In fact, I have determined the magneto-rotary powers and the 

 mean refractive indices of a considerable number of Liquids, con- 

 sisting for the most part of more or less concentrated saline 

 solutionsf. From this preliminary examination aU magnetic 

 liquids were omitted, which, according to the experiments of 

 MM. Bertin and Edmond Beequerel, seemed to be excluded 

 from the law enunciated by M. De la Rive. The indices of rc- 



* Tome 1", p. 556. 



t Almost all the solutions emi)loye(l were prepared and tested under the 

 direction of M. Dcbniy, iu the eheuiical laboratory of the Eeole Norraale 

 supt'ricurc. 



