Prof. QErsted's Experiments on Diamagnetism. 87 



change of position. But we find some attractive diamagnetic 

 bodies, sucli as a piece of iridium in my possession, wood- 

 charcoul and coke, which retain the poles they have accjuired 

 by the influence much longer, of which it is easily to be con- 

 vinced by experiments on the mariner's compass. The ex- 

 perimental investigation of the phaenomena exhibited by these 

 bodies is complicated by this duration of the polarity; but 

 they will probably lead us to discover the connexion which 

 exists between magnetism and diamagnetism. 



When a needle constructed of an attractive diamagnetic 

 substance is suspended above the upper or beneath the lower 

 edge of a polar piece, it assumes a position parallel to this 

 edge. In this parallel position, which might either be per- 

 pendicular to the magnetic axis of the polar piece, or parallel 

 to it, or have quite another position than the figure of the 

 polar piece requires, the disposition of the magnetic forces in 

 the needle is transversal, as in a repellent diamagnetic body ; 

 but with this difference, that its lower part has the opposite 

 magnetism to that of the polar piece, and the upper part that 

 of the same nature. 



I have not succeeded in causing iron to assume the diamag- 

 netic state. An iron wire, of which the diameter is but y\jth 

 of a millimetre, still takes the axial position just as well above 

 the polar faces as between them, and with a force nearly suffi- 

 cient to break the fibre of silk. This experiment has been 

 varied by placing in a quill of a feather, which is repellent, 

 a fragment of the same iron wire, merely 2 millims. in 

 length ; but this arrangement still exhibited the same effects 

 as the iron separately. The same result was also obtained on 

 substituting for the bit of iron wire a very small particle of 

 iron filings ; but on introducing, in the place of iron, a piece 

 of straw which had been immersed in a solution of iron, the 

 diamagnetic effects of attractive bodies was obtained. Nickel 

 gives the same results as iron. Thus nickel and iron ought 

 properly to be called magnetic in the strict sense. This pro- 

 bably applies to some other substances, perhaps to cobalt. 



There is consequently a decreasing magnetic progression 

 which comprises the properly so-called magnetic substances, 

 the attractive diamagnetic substances, and the repulsive dia- 

 magnetic substances. The niagnetism of these last may be 

 considered as negative, if tlie magnetism of iron and the at- 

 tractive diamagnetic substances is regarded as positive. 



The eflf'ect which the polar faces exert upon the attractive 

 diamagnetic bodies is like that which takes place with the re- 

 pulsive diamagnetic bodies, — stronger when the body is placed 

 nearer the upper or lower edges than their intermediate 



