206 Prof. J. A. Ewino; on the Molcculai 



e> 



bristling with difficulties. Many of the phenomena suggest, 

 for instance, the idea that there is a quasi- frictional resistance 

 which opposes the turning of the molecular magnets ; this 

 notion lends itself well to account for the most obvious effects 

 of magnetic hysteresis and the reduction of hysteresis by 

 vibration. On the other hand, it conflicts with the fact that 

 even the feeblest magnetic force induces some magnetism. 

 My object in this paper is to refer to another (and not at all 

 arbitrary) condition of constraint which not only suffices 

 to explain all the phenomena of hysteresis without any notion 

 of friction, but seems to have in it abundant capability to 

 account for every complexity of magnetic quality. 



In describing Weber's theory, Maxwell points out that, if 

 each molecular magnet were perfectly free to turn, the 

 slightest magnetic force would suffice to br«ng the molecules 

 into complete parallelism, and thus to produce magnetic satu- 

 ration. He continues: — li This, however, is not the case. The 

 molecules do not turn with their axes parallel to the force, 

 and this is either because each molecule is acted on by a force 

 tending to preserve it in its original direction, or because an 

 equivalent effect is produced by the mutual action of the 

 entire system of molecules. Weber adopts the former of 

 these suppositions as the simplest.""* 



Weber supposes a directing force to act in the original 

 direction of the molecule's axis which continues to act as a 

 restoring force in that direction after the molecule is dis- 

 turbed. This assumed constraint is quite arbitrary ; more^ 

 over, if it were the only constraint, there would be no residual 

 magnetism when the deflecting force was withdrawn. Accord- 

 ingly, Maxwell modifies Weber's theory by introducing the 

 further assumption that when the angle of deflexion exceeds 

 a certain limit the molecule begins to take permanent set. 

 The development of this, however, does not agree well with 

 the facts. 



The alternative which is offered in the sentence I have 

 quoted from Maxwell was not followed up by him, and seems 

 to have been very generally overlooked, notwithstanding its 

 obvious freedom from arbitrary assumption. Several writers, 

 notably Wiedemann j Jmd Hughes J, have recognized the 

 inter-molecular magnetic forces by suggesting that the mole- 

 cules, when unacted on by any magnetizing force from out- 

 side, may form closed rings, or chains, " so as to satisfy their 



* Maxwell, Electricity and Magnetism, vol. ii. § 443. 

 + Wiedemann, GalvamsmUs, 2nd ed. vol. ii. (1), p. 373. 

 | Hughes, Roy. Sec. Vice May 10, 1883. 



