220 Faraday. 



observed* that certain uniaxal crystals, when placed between 

 the two poles of a magnet, tend to set themselves so that the 

 optic axis has the equatorial position. At this time Faraday 

 was continuing his researches ; and, while investigating the 

 diamagnetic properties of bismuth, was frequently embarrassed 

 by the occurrence of anomalous results. In 1848 he ascertained 

 that these were in some way connected with the crystalline 

 form of the substance, and showedf that when a crystal of 

 bismuth is placed in a field of uniform magnetic force (so that 

 no tendency to motion arises from its diamagnetism) it sets 

 itself so as to have one of its crystalline axes directed along 

 the lines of force. 



At first he supposed this effect to be distinct from that 

 which had been discovered shortly before by Pliicker. " The 

 results," he wrote,J " are altogether very different from those 

 produced by diamagnetic action. They are equally distinct from 

 those discovered and described by Pliicker, in his beautiful 

 researches into the relation of the optic axis to magnetic action ; 

 for there the force is equatorial, whereas here it is axial. So 

 they appear to present to us a new force, or a new form of 

 force, in the molecules of matter, which, for convenience sake, 

 I will conventionally designate by a new word, as the magne- 

 crystallic force." Later in the same year, however, he recognized^ 

 that " the phaenomena discovered by Pliicker and those of which 

 I have given an account have one common origin and cause." 



The idea of the " conduction " of lines of magnetic force by 

 different substances, by which Faraday had so successfully 

 explained the phenomena of diamagnetism, he now applied to 

 the study of the magnetic behaviour of crystals. " If," he wrote,|| 

 "the idea of conduction be applied to these magnecrystallic 

 bodies, it would seem to satisfy all that requires explanation in 

 their special results. A magnecrystallic substance would then 

 be one which in the crystallized state could conduct onwards, or 



* Ann. d. Phys. Ixxii (1847), p. 315; Taylor's Scientific Memoirs, v, p. 353. 



t Phil. Trans., 1849, p. 1 ; Exp. Res., 2454. 



i Exp. Res., 2469. Ibid., 2605. || Ibid., 2837. 



