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XXIY. Intelligence and Miscellaneous Articles. 



NOTE ON DIAMAGNETISM AND CAKNOT's PRINCIPLE. 

 BY OLIVER J. LODGE. 



TN the May 1889 number of the Philosophical Magazine Mr. 

 -■- J. Parker states a series of propositions which are equivalent 

 to the invention of an ingenious perpetual-motion machine, con- 

 sisting of a wheel with a diamagnetic rim spinning near a perma- 

 nent magnet, so that one side of the wheel approaches and the 

 other side recedes from a strong magnetic field. So long as the 

 wheel spins slowly, nothing happens ; but as soon as it spins so 

 fast that the diamagnetism excited lags behind the magnetic force 

 producing it, the side receding from the intense region will be 

 repelled more powerfully than the side approaching from the weak 

 region, and hence there will be perpetual motion. 



There are several ways of getting over this, and one of these 

 Mr. Parker suggests, viz. that diamagnetism may be a thing ex- 

 cited instantaneously ; though naturally he is not much impressed 

 with the likelihood of his suggestion. He rather takes refuge in an 

 appeal against the second law of thermodynamics, as possibly in- 

 applicable to magnetic substances, cycle! -^ being perhaps negative 



for paramagnetic, and positive for diamagnetic, bodies. 



Eeturning to the subject in the last number of the Philosophical 

 Magazine (July 1890), he emerges from this position to make the 

 still wilder suggestion that diamagnetism does not really exist ; 

 that Faraday was deceived throughout his long and acute investi- 

 gation by the obviously disturbing and constantly guarded-against 

 paramagnetism of the air ! 



Would it not, however, be possible that the spinning of a 

 bismuth wheel should exert a demagnetizing effect on a magnet, 

 while the spinning of an iron wheel should exert a strengthening 

 effect ? When one comes to think of it, the ordinary act of mag- 

 netization consists in bringing on a magnet in a weak position and 

 drawing it off in a strong; moreover the hypothetical induced 

 molecular currents of Weber, which would certainly lag behind 

 their cause by reason of self-induction, would get themselves 

 strengthened and weakened as the hypothesis requires. In such 

 case the energy of spin would be obtained at the expense of the 

 magnetic field. 



The diamagnetism of known non-conductors is so disappointingly 

 feeble, and the rapidity of its excitation so exceedingly great (judging 

 from the magneto-optic effect), that it is perhaps not worth while 

 actually to try if a disk of heavy glass delicately suspended and 

 rapidly spun between the poles of a strong magnet in vacuo could 

 maintain its motion. 



University College, Liverpool, 

 July 6, 1890. 



Phil. Mag. S. 5. Vol. 30. No. 183. August 1890. P 



