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LVI. On the Theory of Diamagnetism. Letter fj-om Tvoie&sov 

 Webee to Prof. Tyndall. 



My dear Sir, Gottingen, Sept. 25, 1855. 



ACCEPT my best thanks for your kind communication of the 

 3rd of September ; I am gratified to learn that the apparatus 

 executed by M. Leyser in Leipzig for the demonstration of dia- 

 magnetic polarity has so completely fulfilled your expectations. 

 This intelligence is all the more agreeable to me, inasmuch as 

 before the apparatus was sent away, it was not in my power to 

 go to Leipzig and test the instrument myself. 



It gave me great pleasure to learn that Mr. Faraday and M. 

 De la Rive have had an opportunity of witnessing the experi- 

 ments, and of convincing themselves as to the facts of the case. 



It was also of peculiar interest to me to learn that you had 

 succeeded in establishing the polarity of the self-same heavy glass 

 with which Faraday first discovered diamagnetism. This is the 

 best proof that these experiments do not depend upon the con- 

 ductive power of bismuth for electricity. 



I have read with great interest your memoir " On the Dia- 

 magnetic Force," &c. contained in the Philosophical Transac- 

 tions, vol. cxlv. It has been your care to separate the fact of 

 diamagnetic polarity from the theory, and to place the former 

 beyond the region of doubt. Allow me, with reference to this 

 subject, to direct your attention to a passage at page 39 of your 

 memoir, which you adduce as a conclusion from my theory ; the 

 passage runs as follows : — 



" The magnetism of two iron particles in the line of magnet- 

 ization is increased by their reciprocal action ; but, on the con- 

 trary, the diamagnetism of two bismuth particles lying in this 

 direction is diminished by their reciprocal action." 



This proposition is by no means a necessary assumption of 

 my theory, but is rather a direct consequence of diamagnetic 

 polarity, if the facts be such as both you and I affirm them to 

 be. What, therefore, you have adduced against the above con- 

 clusion must be regarded as an argument against diamagnetic 

 polarity itself. The diamagnetic reciprocal action of the bismuth 

 particles in the line of magnetization is necessarily opposed to 

 the action of the exciting magnetic force. The latter must be 

 enfeebled, because the diamagnetic is opposed to the magnetic 

 reciprocal action of iron particles which lie in the line of mag- 

 netization, through which latter it is known the action of the 

 exciting magnetic force is increased. Hence also the modifica- 

 tion produced in bismuth by nuignctic excitement, whatever it 

 may be, must be weakened, because the force of excitation is 

 diminished. 



