THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1856. 



XXIII. Further Researches on the Polarity of the Diamagnetic 

 Force. By John Tyndall, F.R.S., Membre de la Societe 

 Hollandaise des Sciences ; Foreign Member of the Physical 

 Society of Berlin, and Professor of Natural Philosophy in the 

 Royal Institution^. 



Introduction, 



A YEAR ago I placed before the Royal Society the results of 

 an investigation " On the Nature of the Force by which 

 Bodies are repelled from the Poles of a Magnet t*^^ The simul- 

 taneous exhibition of attraction and repulsion in the case of 

 magnetized iron is the fact on which the idea of the polarity of 

 this substance is founded ; and it resulted from the investiga- 

 tion referred to, that a corresponding duality of action was 

 manifested by bismuth. In those experiments the bismuth was 

 the moveable object upon which fixed magnets were caused to 

 act, and from the deflection of the bismuth its polarity was 

 inferred. But, inasmuch as the action is reciprocal, we ought 

 also to obtain evidence of diamagnetic polarity by reversing the 

 conditions of experiment; by making the magnet the mover 

 able object, and inferring from its deflection the polarity of the 

 mass which produces the deflection. This experiment would be 

 complementary to those described in the communication referred 

 to, and existing circumstances invested the experiment with a 

 great degree of interest and importance. 



In fact an experiment similar to that here indicated was made 

 by Professor W. Weber, previous to my investigation, and the 



* From the Philosophical Transactions for 1856, part i. ; having been 

 received by the Royal Society November 27, 1855, and read December 20, 

 1855. 



t Philosophical Transactions, 1855; andPhil. Mag. for September 1855. 

 Phil Mag. S. 4. Vol. 13. No. 78. Sept, 1856. M 



