162 Professor TyndalVs farthet' Researches 



result was such as to satisfy its author of the reverse polarity of 

 diamagnctic bodies. I will not here enter into a minute descrip- 

 tion of the instrument and mode of experiment by which this 

 result was obtained ; for the instrument made use of in the pre- 

 sent inquiry being simply a refinement of that made use of by 

 M. Weber, its explanation will embrace the explanation of his 

 apparatus. For the general comprehension of the criticisms to 

 which M. Weber's resuHs have been subjected, it is necessary, 

 however, to remark, that in his experiments, a bismuth bar, 

 within a vertical spiral of copper wire, through which an electric 

 current was transmitted, was caused to act upon a steel magnet 

 freely suspended without the spiral. When the two ends of the 

 bar of bismuth were permitted to act successively upon the sus 

 pended magnet, a motion of the latter was observed, which in- 

 dicated that the bismuth bar was polar, and that its polarity was 

 the reverse of that of iron. 



Notwithstanding the acknowledged eminence of M. Weber 

 as an experimenter, this result failed to produce general convic- 

 tion. Mr. Faraday, in his paper " On the polar or other^ con- 

 dition of diamagnetic bodies *,'' had shown that results quite 

 similar to those obtained by M. Weber, in his first investigation 

 with bismuth, were obtained in a greatly exalted degree, with 

 gold, silver and copper; the eflfect being one of induction, 

 and not one due to diamagnetic polarity. He by no means 

 asserted that his results had the same origin as those obtained 

 by M. Weber ; but as the latter philosopher had made no men- 

 tion of the source of error which Mr. Faraday's experiments 

 rendered manifest, it was natural to suppose that it had been 

 overlooked, and the observed action attributed to a wrong 

 cause. In an article published in his ' Massbestimmungen ' in 

 1852, M. Weber, however, with reference to this point, writes 

 as follows : — ''J will remark that the article transferred from the 

 Reports of the Society of Sciences of Saxony to PoggendorfF's 

 Annalen was only a preliminary notice of my investigation, 

 the special discussion of which was reserved for a subsequent 

 communication. It will be sufficient to state here, that in the 

 experiments referred to I sought to eliminate the inductive 

 action by suitable combinations ; but it is certainly far better to 

 set aside this action altogether, as has been done in the experi- 

 ments described in the present memoir.'' 



One conviction grew and strengthened throughout these dis- 

 cussions — this, namely, that in experiments on diamagnetic 

 polarity great caution is required to separate the pure effects of 

 diamagnetism from those of ordinary induction. With refer- 



* Experimental Researches, 2640, Philosophical Transactions, 1850 

 p. 171. 



