164 Professor TyndalPs further Researches 



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 essays with metals possessing a higher conducti- 

 bility than bismuth, that the same end could be obtamed. I 

 cannot leave you ignorant that the doubts which I have ventured 

 to advance against the experiments of M. Weber are supported 

 by the negative result which I have obtained in endeavouiing to 

 excite diamagnetic polarity in bismuth by the discharge of the . 

 Leyden jar/' 



It will be seen in the following pages that the conditions laid 

 down by M. Matteucci for the rigorous demonstration of diamag- 

 netic polarity are more than fulfilled. 



The conclusions of M. Weber find a still more strenuous 

 opponent in his countryman 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 of by using, instead of a dia- 

 magnetic conductor, a diamagnetic insulator.'^ To test the ques- 

 tion, 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 magnet to oscillate, or to bring the 

 magnet from a state of oscillation to one of rest." M. v. Fei- 

 litzsch pushes his experiments further, and finds that when the 

 bismuth is motionless within its spiral, the position of the mag- 

 net is just the same as when the bismuth is entirely withdrawn ; 

 hence his final conclusion, that the deflection of the magnet in 

 Weber's experiments is due to induced currents, which are ex- 

 cited in the bismuth by its mechanical motion up and down 

 within the spiral. 



These divergent opinions upon a question of such vital bearing 

 upon the general theoiy of magnetic phsenomena, naturally ex- 

 cited in me the desire to make myself acquainted with the exact 

 value of M. Weber's experiments. The most direct way of 

 accomplishing this I consider to be, to operate with an instru- 

 * Poggendorflf's Annalm, xcii. 377. 



