408 Prof. Weber on the Theonj of Diamagnetism. 



(I believe, however, that this argument against diamagnetic 

 polarity may also be surmounted. The phfeuomenon which 

 you have observed must be referred to other circumstances, also 

 connected with the compression of the bismuth. For the dia- 

 magnetic reciprocal action is, as I have shown, much too weak 

 to produce an effect which could be compared in point of mag- 

 nitude with the reciprocal action produced in the case of iron.) 



I take this opportunity of adding a few remarks for the pur- 

 pose of setting my theory of diamagnetic polarity in a more 

 correct light. 



My theory assumes : — 1, that the fact of diamagnetic polarity 

 is granted ; 3, that in regard to magnetic phisnomena, Poisson's 

 theory of two magnetic fluids, and Ampere's theory of molecular 

 currents, are equally admissible. Whoever denies the first fact, 

 or rejects the theory of Ampere, cannot, I am ready to confess, 

 accept my theory. 



But supposing that you do not reject Ampere's theory of per- 

 manent molecular currents, but are disposed to enter upon the 

 inner connexion and true significance of the theory, you will 

 easily recognize that it is by no means an arbitrary assumjMon 

 of mine, that in bismuth molecular currents are excited, when 

 the exciting magnetic force is augmented or diminished; but 

 that the excitation of such molecular currents is a necessary con- 

 elusion from the theory of Ampere, which conclusion Ampere 

 himself could not make, because the laws of voltaic induction, 

 discovered by Faraday, were unknown to him. In all cases 

 where molecular currents exist, by increase or diminution of the 

 magnetic exciting force molecular currents must be excited, which 

 either add their action to, or subtract it from, the action of those 

 already pi'esent. 



Finally, permit me to make a few remarks on the following 

 words of your memoir : — 



" To carry out the assumption here made, M. Weber is obliged 

 to suppose that the molecules of diamagnetic bodies are sur- 

 rounded by channels, in which the induced currents, once excited, 

 continue to flow without resistance." 



The assumption of channels which surround the molecules, 

 and in which the electric fluids move without resistance, is an 

 assumption contained in the theory of Ampere, and is by no 

 means added by me for the purpose of explaining diamagnetic 

 polarity. A permanent molecular current ivithout siich a channel 

 involves a manifest contradiction, according to the law of Ohm. 



I may further observe, that I do not wonder that you regard 

 a theory which is built upon the assumption of such channels, as 

 " so extremely artificial that you imagine the general conviction 

 of its truth cannot be very sti'ong." In a certain sense 1 quite 



