348 DIAMAGXETIC POLARITY. SECT. XXXIV. 



magnet, which returns to its original position when the current 

 ceases. When, on the contrary, the magnetism is permanent, 

 the suspended magnet does not return to its original position 

 when the current ceases. In Professor Tyndall's experiment the 

 deviation was permanent, and it was equally so when a bismuth 

 bar was freely suspended and the cores within the spirals were 

 steel magnets. Had the effect been from currents induced in the 

 mass of the bar of bismuth, division of the bar would have stopped 

 them, but the result was the same with powdered bismuth as 

 with the solid mass. Moreover, since the strength of induced 

 currents depends upon the conducting power of the substance, 

 and as the conducting power of copper is forty times as great as 

 that of bismuth, had the polarity been induced and not real, the 

 effect ought to have been forty times greater when copper instead 

 of bismuth cores were put in the spirals, whereas it was scarcely 

 sensible. Besides these proofs, Dr. Tyndall made experiments 

 with eleven Different diamagnetic substances, of which water was 

 one, with similar results. He then determined the polarity of 

 twelve paramagnetic bodies by the same method, whence it 

 appeared that the same action which produced a north pole in 

 the paramagnetic bodies produced a south pole in those that 

 were diamagnetic, and vice versa, whence he concludes that dia- 

 magnetic polarity is one of the most firmly established truths of 

 science. It follows from this that, when a man is standing, his 

 head is a north pole and his feet a south, and the top of an iron 

 railing on which he may be leaning is a south pole and the lower 

 end a north. Diamagnetic bodies thus possess a polarity, the 

 same in kind but opposite in direction to that possessed by para- 

 magnetic ones.* They are both dual powers, and the two dia- 

 magnetic forces like the two paramagnetic being coexistent, 

 simultaneous, and mutually dependent, there can be no doubt 

 that the diamagnetic forces also are represented, or rather consist 

 of curved and closed lines of force passing through the interior 

 of the substance. Dr. Tyndall has proved that the attraction 

 of iron, and the repulsion of bismuth, are as the square of the 

 electro-magnetic current producing them, and that diamagnetic 

 substances are capable of induction. 



* Professor Matteucci still expresses doubts on this subject, but has not 

 yet finished his experiments. 



