on the Polarity of the Diamagnetic Force. 163 



ence to even the most recent experiments of M. Weber — those 

 to which he has referred at the conclusion of the above citation 

 — it is strongly urged that there is no assurance that the sepa- 

 ration referred to has been effected. In those experiments, as 

 already stated, a cylinder of bismuth was suspended within a 

 vertical helix of covered copper wire, and the action of the 

 cylinder upon a magnet suspended opposite to the centre or 

 neutral point of the helix was observed. To increase the action, 

 the position of the cylinder was changed at each termination of 

 the minute swing of the magnet, the amplitude of the oscillations 

 being thus increased, and the effect rendered more sensible to 

 the eye. Now, it is urged, there is every reason to believe that 

 in these motions of a metallic mass within an excited helix' 

 induced currents will be developed, which, acting upon the 

 magnet, will produce the motions observed. The failure indeed 

 to demonstrate the existence of diamagnetic polarity by other 

 means has, in the case of some investigators, converted this 

 belief into a certainty. 



Among the number whom M. Weber^s experiments have failed 

 to convince, M. Matteucci occupies a prominent place. With 

 reference to the question before us this philosopher writes as 

 follows*:— "In reading the description of the experiments of 

 M. Weber, we are struck on beholding the effects produced by 

 moving the bismuth when there is no current in the spiral. 

 Although the direction of oscillation in this latter case is opposed 

 to that observed when the spiral is active, still the fact excites 

 doubts as to the truth of the conclusions which have been drawn 

 from these experiments f- To deduce rigorously the demonstra- 

 tion of diamagnetic polarity, it would he necessary to substitute for 

 the bismuth, masses formed of insulated fragments of the metal X, 

 to vary the dimensions of the cylinder, and above all, to compare 

 the effects thus obtained with those which would probably be obtained 

 with cylinders of copper and silver in a state of purity. 



" We are obliged to make the same remarks on another series 

 of experiments which this physicist has made to obtain anew, 

 by the effects of induction, the proof of diamagnetic polarity. 



* Cours Special sur V Induction, p. 206. 



t It is not ray place to account for the effect here referred to. I may 

 however remark, that there appears to be no difficulty in referring it to the 

 ordinary action of a diamagnetic body upon a magnet. It is the result 

 which Brugmann published upwards of half a century ago ; the peculiar 

 form of this result in one of the series of experiments quoted by M. Weber 

 must, I think, be regarded as purely accidental. — J. T. 



X Also in page 201 : — " II fallait done, pour prouver si I'influence d'un 

 corps diamagnetique produit sur un aimant une variation de sens contraire 

 h. celle developpee dans le fer doux, operer avec ce corps prive de conduc- 

 tihilite." 



M2 



