1881.] Molecular Electro-Magnetic Induction. 



529 



netism became symmetrical ; and his theory, I believe, is fully capable 

 of explaining the effects I have obtained, if we admit that we can 

 rotate the paths of the polarised molecules by an elastic torsion. 



Matteucci made use of an inducing and secondary coil in the year 

 1847,* by means of which he observed that mechanical strains in- 

 creased or depressed the magnetism of a bar inside this coil. 



Wertheim published in the " Comptes Rendus," 1852, f some results 

 similar to Matteucci ; but in the " Annales de Chimie et de Physique," 

 1857,| he published a long series of most remarkable experiments, in 

 which he clearly proves the influence of torsion upon the increment or 

 decrement of a magnetical wire. 



Vilari showed§ increase or diminution of magnetism by longitudinal 

 pull according as the magnetising force is less or greater than a certain 

 critical value. 



Wiedemann, || in his remarkable work " Galvanismus, " says that an 

 iron wire through which an electric current is flowing becomes mag- 

 netised by twisting the wire. This effect I have repeated, but found 

 the effects very weak, no doubt due to the weak battery I use, viz., 

 four quart bichromate cells. 



Sir W. Thomson shows clearly in his remarkable paper " Effects of 

 Stress on the Magnetisation of Iron, Nickel, and Cobalt, "^[ the critical 

 value of the magnetisation of these metals under varying stress, and 

 also explains the longitudinal magnetism produced by Wiedemann as 

 due to the outside molar twist of the wire, making the current pass as 

 in a spiral round a fixed centre. Sir William Thomson also shows 

 clearly the effects of longitudinal as well as transversal strain, both as 

 regards its molar magnetism and its electric conductivity. 



My own researches convince me that we have in molecular mag- 

 netism a distinct and separate form of magnetism from that when we 

 develop, or render evident, longitudinal or transversal magnetism, 

 which I have before defined as molar. 



Molecular magnetism is developed by any slight strain or twist 

 other than longitudinal, and it is only developed by an elastic twist ; 

 for, however much we may twist a wire, provided that its fibres are 

 not separated, we shall only have the result due to the reaction of its 

 remaining elasticity. 



If we place an iron wire, say 20 centims. long, 1 millim. diameter, in 

 the axis of the coil of the electro-magnetic balance, and if this wire is 

 joined, as described, to the telephone, we find that on passing a electric 



* " Compt. Send.," t. xxiv, p. 301, 1847. 



f " Compt. Rend.," t. xxv, p. 702, 1852. 



X "Ann. de Chim. et de Phys.," (3), t. 1, p. 385, 1857. 



§ " Poggendorff's Annalen," 1868. 



!| Wiedemann. " Gralvanismus," p. 447. 



IF " Phil. Trans.," 1879, p. 55. 



