86 Prof. CErsted's Experiments on Diamagnetism. 



100 oscillations in the same time. Above the polar pieces, in 

 the axial position, the needle made only nineteen oscillations 

 in the same time. These experiments have been sufficiently 

 repeated and varied to afford the most perfect certainty as to 

 what has been stated ; but the investigations have not yet 

 been carried far enough to admit of an accurate numerical 

 law being deduced from them. 



When a horizontal needle of bismuth is suspended by a 

 fibre of silk to the extremity of a balance, so that the balance 

 can be raised or lowered, the needle is found to be repelled 

 with so much more force the nearer it is situated to one of the 

 edges of the polar faces. It will be understood that this re- 

 pelling power causes the needle to ascend when it is near the 

 upper edges, and to descend when near the lower edges ; in the 

 intermediate position it neither ascends nor descends. When 

 the needle is suspended above the polar pieces, and conse- 

 quently in the direction perpendicular to the edges of the 

 polar faces, it is again re[)elled, but much more feebly than 

 when in the equatorial position. 



Hitherto diamagnetic effects had only been observed in 

 bodies which are repelled by the two poles of the magnet. My 

 experiments have shown that a similar effect may be produced 

 in most bodies which are attracted by the two magnetic poles; 

 so that these bodies constitute a new kind of diamagnetic sub- 

 stances. These two classes may be distinguished by the names 

 o^ repulsive and attractixie diamagnetic bodies. 



A needle made of a substance that is attracted by the mag- 

 net, but of which the magnetism is not of the same nature as 

 that of iron and nickel, when suspended between the two polar 

 faces of the electro-magnet, acquires, as is well known, the 

 position called axial by Mr. Faraday ; but if it is raised above 

 the upper edges, or lowered beneath the lower edges of the 

 polar faces, it assumes the equatorial position. This property 

 has hitherto been found in the following substances ; viz. pla- 

 tiiia, palladium, iridium, titanium, an alloy of 0"S25 of tin, 

 0*024 of bismuth, 0*108 of ii*on, in brass, German silver, wood- 

 charcoal, coke (fossil coal belongs to the repulsive diamag- 

 netic bodies), obsidian, native carbonate of iron, attractive 

 glass, Prussian blue, and solutions of iron. 



In the majority of these substances, the magnetic poles which 

 they obtain during the influence of the electro-magnet disap- 

 pear nearly as soon as this influence is removed ; however, 

 their existence is betrayed when the poles of the electro-magnet 

 are suddenly changed, for then many of these bodies turn half 

 round, as is the case with a magnetic needle ; others do not 

 exactly turn, but oscillate, thus indicating their tendency to a 



