579 



Article XVII. 



On a siinj)le Method of increasing the Diamagnetisirt'of Oscillating 

 Bodies: Diamagnetic Polarity. By Prof. Plucker. 



'. .!> •jiii :'_■■ 

 [From PoggendorfF's Annalen for March 1818.] tdivn ylflo 



1. JtARADAY'S fundamental experiment may even be re- 

 peated with a feeble steel magnet ; and it can thus be shown 

 that a bar of bismuth, when suspended by means of a silk- 

 worm thread between its two poles, is repelled by them, and 

 settles in the equatorial position. But the diamagnetic repul- 

 sion of bismuth is very slight in comparison with the magnetic 

 attraction of iron ; hence every means of increasing the diamag- 

 netic force is desirable. A means of effecting this is obtained 

 by merely placing close beneath the oscillating bar of bismuth a 

 bar of iron, arranged equatorially in the middle of the space be- 

 tween the two poles of the horseshoe iron magnet, and fixing it 

 in this position. It is at once evident that the bar of bismuth 

 then tends to assume the equatorial position with greater force ; 

 and it is easy, by the oscillating method, to determine the pro- 

 portion in which the diamagnetic directive force has become 

 increased by the application of the iron bar. 



2. Among other experiments I made the following: — I placed 

 the two halves of the keeper C (see par. 2 of the preceding me- 

 moir) in such a manner upon the large electro-magnet, with their 

 grooves downwards, that their rectangular terminal surfaces 

 were turned towards each other and formed the surfaces of the 

 poles. They were 40 milliras. in height, 59 millims. broad in 

 the equatorial direction, and were kept at a constant distance of 

 16*5 millims. by placing between them two pieces of brass, each 

 of which was G millims. in thickness, and in the middle enclosed 

 an iron bar 4*5 millims. in thickness and as long as the breadth 

 of the surfaces of the poles. A small cylinder of bismuth, 2 

 millims. thick and 25 millims. long, when suspended by a silk- 

 worm thread so as to oscillate between the surfaces of the poles 

 at a level somewhat below that of their upper angles and close 



