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A paper was also in part read, entitled " Experimental Researches 

 in Electricity." Twenty-third Series. § 29. On the Polar or other 

 condition of Diaraagnetic Bodies. By Michael Faraday, Esq., 

 F.R.8. &c. 



March 14, 1850. 



GEORGE RENNIE, Esq., Vice-President and Treasurer, in 

 the Chair. 



The reading of Dr. Faraday's paper, entitled " Experimental Re- 

 searches in Electricity. Twenty-third Series. § 29. On the Polar 

 or other condition of Diamagnetic Bodies:" was resumed and con- 

 cluded. 



The author, whilst developing, on a former occasion, the pheno- 

 mena of diamagnetic action, said that all the results might be ac- 

 counted for by assuming that bismuth, phosphorus, &c., when in 

 the magnetic field, became polar as iron is polar, but with the poles 

 in the contrary direction. This view has since then been adopted 

 by Weber and others, and supported by certain experimental results. 

 In the present paper these results and that view are brought under 

 very close examination. An apparatus was constructed by which a 

 cylinder of any given metal could be moved to and fro through 

 about two inches in the direction of its axis. In doing this it 

 approached close up to, and then retreated from the pole of an 

 electro-magnet, and also moved within a helix of covered wire which 

 was fixed in relation to the magnet. Now the action of such a piece 

 of metal upon the helix is very different in theory, and also in reality, 

 according as it is dependent upon a polarity, magnetic or diamag- 

 netic, acquired by the metal, or upon induced currents existing in 

 the mass ; and the question was to ascertain by experiment whether 

 the latter were the cause of the results obtained by Weber and 

 others. The various diamagnetic metals gave the results looked for 

 at the indicating galvanometer ; but then these were almost insensible 

 with bismuth, and were greatest with gold, silver, copper, and the 

 better conductors, being indeed in proportion to the conducting 

 power. Such results were in favour of induced currents rather than 

 of polarity. Division was next resorted to as a distinguishing test 

 of the polar or current action ; thus a cylinder made up of lengths 

 of wires acted as well as a solid cylinder, if the metal were one 

 acquiring a polar state as iron ; but such a division interfered with 

 the existence of induced currents in the mass, and it was found that 

 such wire cylinders of copper, &c. lost all power. On the other 

 hand, division of the cylinder into innumerable discs interfered greatly 

 with polarity, but not at all with the induced currents, nor with the 

 action of the diamagnetic metals. The places of maximum and 

 minimum action of a cylinder of metal are very different according 

 as that metal acts by a polar condition, or by currents induced in the 

 mass : it is shown by experiments with the diamagnetic metals that 



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