SECT. XXXIV. DIAMAGNETIC POLARITY. 347 



and planets, in all their secular and periodic changes, may cause 

 perpetual variations in terrestrial magnetism, and it may not be 

 beyond the delicacy of modern observation to ascertain whether 

 a planet, when nearest to the earth, has any sensible magnetism. 



Diamagnetism is also a dual power, but in complete antithesis 

 to paramagnetism under the same circumstances. Dr. Faraday 

 first discovered this property in heavy glass, or silico-borate of 

 lead, a piece of which was repelled by the pole of a powerful 

 electro-magnet, and an elongated prism of the same heavy glass, 

 when freely suspended between the poles, set equatorially. He 

 then found that so great a number of substances followed the 

 same law, that it established the very remarkable fact of a 

 hitherto unknown force having acted upon the substances sub- 

 mitted to its influence, a discovery which he subsequently con- 

 firmed by many experiments, all of which proved the antithesis 

 between the two modes of magnetic action. He also discovered 

 that magnetic bodies differ exceedingly in their magnetic power : 

 of paramagnetic bodies iron is the most powerful ; then follow 

 nickel, cobalt, and a long gradation down to osmium and a 

 vacuum. The body that seems to have the lowest diamagnetic 

 power is arsenic, and the series ascends to heavy glass, antimony, 

 phosphorus, and bismuth ; so iron and bismuth are the most 

 powerful in their respective classes, and both have a small con- 

 ducting power for electricity. It may be presumed that many 

 remarkable instances of diamagnetism are to be met with in 

 nature ; among others, Dr. Faraday has suggested the idea that 

 Saturn's ring, from its position, may be diamagnetic with regard 

 to the planet. 



With very powerful magnets or electro-magnets, which are 

 absolutely necessary for all these experiments, it is found that no 

 simple substance is neutral, but that such may be compounded 

 by mixing in due proportion a diamagnetic and paramagnetic 

 liquid, as water and protosulphate of iron. 



Professor Tyndall proved diamagnetic polarity by placing two 

 bismuth bars within two vertical coils or spirals of insulated 

 copper wire, through which electric currents were transmitted 

 from a galvanic battery, and caused to act upon a steel magnet 

 freely suspended without the spirals. Now, when the excited 

 magnetism is merely by induction, the electric current, being 

 momentary, only causes a shock or momentary deviation in the 



