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XI. Further Researches on the Polarity of the Diamagnetic Force. By John Tyndall, 
F.R.S., Memhre de la Socidtd Hollandaise des Sciences ; Foreign Member of the 
Physical Society of Berlin, and Professor of Natural Philosophy in the Royal 
Institution. 
Received November 27, — Read December 20, 1855. 
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*.” 
The simultaneous 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 investigation 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 moveable 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 result was such as to satisfy its 
author of the reverse polarity of diamagnetic bodies. I will not here enter into a 
minute description of the instrument and mode of experiment by which this result 
was obtained ; for the instrument made use of in the present inquiry being simply a 
refinement of that made use of by M. Weber, its explanation will embrace the 
explanation of his apparatus. For the general comprehension of the criticisms to 
which M. Weber’s results have been subjected, it is necessary, however, to remark, 
that in his experiments a bismuth bar, within a vertical spiral of copper wire, through 
which an electric current was transmitted, was caused to act upon a steel magnet 
freely suspended without the spiral. When the two ends of the bar of bismuth were 
permitted to act successively upon the suspended magnet, a motion of the latter was 
observed, which indicated that the bismuth bar was polar, and that its polarity was 
the reverse of that of iron. 
Notwithstanding the acknowledged eminence of M. Weber as an experimenter, 
* Philosophical Transactions, 1854. 
MDCCCLVI. 2 I 
