238 
PROFESSOR TYNDALL’S FURTHER RESEARCHES 
this result failed to produce general conviction. Mr. Faraday, in his paper “On the 
polar or other condition 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 effect 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 mention of the source of error which Mr. Faraday’s expe- 
riments 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 
‘ Massbestirnmungen’ in 1852, M. Weber, however, with reference to this point, 
writes as follows : — “ I 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 sub- 
sequent 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 
experiments described in the present memoir.” 
One conviction grew and strengthened throughout these discussions — this, namely, 
that in experiments on diamagnetic polarity great caution is required to separate the 
pure effects of diamagnetism from those of ordinary induetion. With reference 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 separation 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 deve- 
loped, 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-l-: — “In reading the description of the expe- 
riments 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 oscil- 
lation in this latter case is opposed to that observed when the spiral is active, still 
* Experimental Researches, 2640, Philosophical Transactions, 1850, p. 171. 
t Cours Special sur ITnduction, p. 206. 
