1883.] Theory of Magnetism based on New Researches. 181 



tions upon magnetism, since which time numerous researches have 

 been made by means of torsion. 



Matteucci* employed induction currents, by means of which he 

 observed that mechanical strains increased or decreased the magnetism 

 of a bar of iron. 



Wertheimf published a long series of most remarkable experiments, 

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

 or decrement of a magnetic wire. 



Wiedemann]; published his interesting experiments upon torsion- 

 flexion in relation to magnetism, and in his remarkable work, " Galva- 

 nismus," 1861, relates his discovery of magnetism produced in an iron 

 wire upon the passage or after of an electric current. He also gives 

 a molecular theory of magnetism, similar to that of De La Rive, 1853, 

 except that Wiedemann supposes that neutrality is the result of a 

 heterogeneous arrangement, thus differing completely from the 

 symmetrical neutrality that I have defined. 



Villari§ showed increase or diminution of magnetism by longitu- 

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

 certain value. 



Gore, || in numerous interesting experiments, shows the influence of 

 electric torsion and the identity of molecular sounds. 



Sir W. Thomson,^" in a remarkable paper, shows the critical value 

 of the magnetisation of iron, nickel, and cobalt under varying stress, 

 and also the effects of longitudinal as well as transversal strain upon 

 its electric conductivity. 



Tomlinson** has recently shown completely the influence of strain 

 upon the conductivity of all metals, and that strain produces a mole- 

 cular change in their structure. 



These employed each a somewhat different method, either by 

 primary or secondary currents acting upon a galvanometer or the 

 action of magnetism upon a magnetic needle. 



This field of research has been so thoroughly examined that I should 

 have hesitated before trying to reproduce the results by ordinary 

 or similar means. The induction balance, however, seemed to me 

 peculiarly adapted, from its extreme sensitiveness to molecular changes 

 of structure, to analyse such changes as are produced by magnetism. 

 T have put its powers to use in the following researches, and, as I 

 have necessarily studied all the phases of magnetism, I have been 



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



f "Ann. de China, et de Phys.," (3), t. 1, p. 385, 1857. 



X "Archives," t. xxxv, p. 39, et tome ii (nour. periode), p. 300. 



§ " PoggendorfE's Annalen," 1868. 



|| " Phil. Trans.," 1874. 

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

 ** " Phil. Trans.," Part I, 1883. 



