ON THE POLARITY OF THE DIAMAGNETIC FORCE. 
239 
the fact excites doubts as to the truth of the conclusions which have been drawn 
from these experiments*. To deduce rigorously the demonstration of diamagnetic 
polarity, it would be necessary to substitute for the bismuth, masses formed of insulated 
fragments of the metal\, to vary the dimensions of the cylinder, and above all, to com- 
pare the effects thus obtained with those which would probably be obtained with cylin- 
ders 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. It is astonishing that after having sought to neutralize 
the development of induced currents in the moving cylinders of bismuth, by means 
of a very ingenious disposition of the spiral — it is astonishing, I repeat, that no 
attempt was made to prove by preliminary ^ssays with metals possessing a higher 
conductibility than bismuth, that the same end could be obtained. I cannot leave 
you ignorant that the doubts which I have ventured to advance against the experi- 
ments of M. Weber are supported by the negative result which I have obtained in 
endeavouring to excite diamagnetic polarity in bismuth by the discharge of the Ley- 
den jar.” 
It will be seen in the following pages that the conditions laid down by M. Mat- 
TEucci for the rigorous demonstration of diamagnetic polarity are more than ful- 
filled. 
The conclusions of M. Weber find a still more strenuous opponent in his country- 
man Professor v. Feilitzsch, who has repeated Weber’s experiments, obtained his 
results, but who denies the validity of his inferences. M. v. Feilitzsch argues that 
in the experiments referred to it is impossible to shut out ordinary induction, and 
for the rigorous proof of diamagnetic polarity proposes the following conditions^. 
To render the experiment free from the action of induced currents two ways are 
open. The currents can be so guided that they shall mutually neutralize each other’s 
action upon the magnet, or the induced currents can be completely got rid ^ by using, 
instead of a diamagnetic conductor, a diamagnetic insulator." To test the question, 
M. V. Feilitzsch resorted to the latter method : instead of cylinders of bismuth he 
made use of cylinders of wax, and also of a prism of heavy glass, but in neither case 
was he able to detect the slightest action upon the magnet. “ However the motions 
of the prism might be varied, it was not possible either to cause the motionless mag- 
net to oscillate, or to bring the magnet from a state of oscillation to one of rest.” 
* It is not my 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. 
t Also in page 204 : — “ II fallait done, pour prouver si I’influence d’un corps diamagnetique produit sur un 
aimant une variation de sens contraire k celle developpee dans le fer doux, opdrer avec ce corps prive de con- 
ductibilit^.” 
J Poggendorff’s Annalen, xcii. 377. 
I 
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