Dr. Faraday on the Magnetic Affection of Light. 251 



produced in steel or in soft iron by the influence of a mngnet, 

 differ from those which occur in all bodies, in this ; that in 

 the first the distribution of magnetism is always in the direc- 

 tion of the length, whilst in tritoxide of iron, wood, gum- 

 lac, &c, it occurs generally in a transverse direction, espe- 

 cially when they are formed into needles. This difference of 

 effect is due to the circumstance, that the magnetism- being 

 very weak in these bodies, we may neglect the reaction of. 

 the particles of the bodies on themselves." These words, and 

 the time of their publication (January 1846), sufficiently show 

 that M. Becquerel does not admit the new form or condition 

 of magnetic action, which I supposed I had previously de- 

 monstrated. 



M. E. Becquerel, in a communication to the Academy of the 

 date of June 1846*, after confirming the action on light which 

 I had announced, touches the question of magnetic action on 

 all bodies; and at this late period is still of the same opinion 

 as his father. I need quote only a few brief lines here and there 

 to show this state of his mind. After speaking of Coulomb's 

 results, and of his father's in 1827, he says, "These experi- 

 ments have been made nearly twenty years, and nevertheless 

 M. Faraday has announced anew the phenomenon of trans- 

 verse direction, has made of the bodies which place them- 

 selves thus a new class of substances, and has named them 



diamagnetic substances I ask myself how, under 



these circumstances, one can push the spirit of classification 

 thus far, when one may give to the same substance all the va- 

 rious positions of longitudinal, transverse or oblique. In fact, 

 place the two extremities of two strong magnets opposite each 

 other, at 0*08 or 012 of an inch apart, and at about 0*04 from 

 their surface, suspend by means of cocoon silk, a small needle 

 of wood or of copper, about 0*04 in diameter and 1*9 or 2*3 

 inches long, it will place itself transversely. If the needle be 

 cut in two and again divided, &c, we shall end by having a 

 fragment, which will place itself in the line of the poles. It 

 is simply a phenomenon of the resultant forces ; for we may 

 give to one and the same substance these different positions, 

 according to its form, by modifying the distance of the poles." 

 Then, speaking of the small quantity of iron which he found 

 in certain specimens, and of his former statement, that these 

 substances behaved as a mixture of inert matter and magnetic 

 particles, or as ferruginous mixtures, he says, "all these con- 

 clusions still subsist at this day in all their generality." 



These conclusions from two profound philosophers, so well 



* Comptes Rendus, 1846, p. 595. 

 S2 



