432 Prof. A. de la Rive's Memoir of 



stances on which this repulsive action of the magnet is most di- 

 stinctly exerted ; but all bodies in nature which are not magnetic 

 (and these are by far the most numerous) present the same pro- 

 perty, although in various degrees. In this way Faraday comes 

 to class all bodies under two heads : — those which are magnetic, 

 or paramagnetic, as he calls them, such as iron, nickel, &c. ; and 

 those which are diamagnetic, such as bismuth, antimony, heavy 

 glass, &c. The character of the former is to be attracted by the 

 magnet, that of the latter to be repelled by it. It is true that 

 this repulsion, to become sensible, requires an enormous mag- 

 netic power, even in the case of bodies of which the diamagne- 

 tism is most strongly marked, whilst a very weak magnet is 

 sufficient to betray its action upon the magnetic bodies, such as 

 iron, steel, nickel, &c. 



It therefore required very powerful means, such as Faraday 

 employed, for the discovery of diamagnetism. Nevertheless a 

 distinguished amateur in science, M. Lebaillif of Paris, had shown, 

 as early as 1828, that a fragment of bismuth or antimony very 

 evidently repels a delicately suspended magnetized needle when 

 brought as near as possible to one of the poles of the needle but 

 without touching it. Mr. Faraday was ignorant of this circum- 

 stance when he published his first work on diamagnetism. I 

 immediately informed him of it, at the same time indicating the 

 journal in which I had published M. Lebaillif s experiment, which 

 I had witnessed at the time. He accepted my reclamation in 

 the most amicable manner, and at once, with his usual good faith, 

 recognized the priority of M. Lebaillif with regard to bismuth 

 and antimony. 



In the numerous researches which Faraday devoted (from 

 1845 to 1855) to diamagnetism and at the same time to mag- 

 netism, there are some important points which I must indicate. 

 He discovered the remarkable influence exerted upon this kind 

 of properties by the molecular constitution of bodies, and espe- 

 cially by crystallization. He showed, for example, that a crys- 

 tallized lamina of bismuth or antimony can place itself axially 

 between the poles of an electromagnet like a magnetic body, as 

 well as equatorially, and that the position which it takes depends 

 on the manner in which it is suspended relatively to the direc- 

 tion of its cleavage. He endeavoured to investigate the force 

 which comes into play in facts of this order, which he names 

 magneto crystalline force; whilst Pliicker, on his part, widened 

 its field by his beautiful and numerous researches on the man- 

 ners in which crystals place themselves between the poles of an 

 electromagnet ; and Tyndall, the worthy successor of Faraday 

 at the Pioyai Institution, by his ingenious experiments analyzed 

 the phenomenon in its generality and succeeded in connecting it, 



