286 Prof. Tyudali on the Nature of the Force by which 



it follows that a very slight deviation of the box from the equa- 

 torial position is sufficient to give the moment of ^' a prepon- 

 derance over that of ^, and consequently to produce the exact 

 effect observed in the experiment. 



The consistency of this reasoning is still further shown when 

 we operate in a field of force which diminishes speedily in inten- 

 sity as we recede from the magnet. Such a iield is the space 

 immediately in front of pointed poles. Suspending our rectan- 

 gular box between the points, and causing the latter to approach 

 until the box has barely room to swhig between them, it is im- 

 possible to produce the phscnomena which we have just described. 

 The intensity with which the nearest points of the bismuth bar 

 are repelled so much exceeds the attraction of the more distant 

 end, that the moment of attraction is not able to cope success- 

 fully with the moment of repulsion ; the bars are consequently 

 repelled en masse, and the length of the box takes up a position 

 at right angles to the line which unites the poles. 



It is manifest, however, that by increasing the distance be- 

 tween the bismuth bar and the points acting upon it, we dimi- 

 nish the difference of action upon the two ends of the bar. When 

 the distance is sufficient, we can produce, with the pointed poles, 

 all the phseromena exhibited between Hat or rounded ones. 



All the effects which have been described are produced with 

 great distinctness w^hen, instead of compressed bismuth, two 

 similar bars of the crystallized substance are used, in which the 

 planes of principal cleavage are parallel to the length. Such 

 bars are not difficult to procure, and they ought to hang in the 

 magnetic field -mih. the planes of cleavage vertical. It is unne- 

 cessary to describe the experiments made with such bars ; they 

 exhibit with promptness and decision all the effects observed with 

 the compressed bismuth. 



We have hitherto operated upon elongated masses of bismuth; 

 but with the compressed substance, or with the substance cry- 

 stallized uniformly in planes, as in the case last referred to, an 

 elongation of the mass is not necessary to the production of the 

 effects described. Previous, however, to the demonstration of 

 this proposition, I shall introduce a kind of lemma, which will 

 prepare the way for the complete proof. 



Diamagnetic bodies, like paramagnetic ones, vary considerably 

 in the intensity of their forces. Bismuth or antimony, for ex- 

 ample, exhibits the diamagnetic force with greater energy than 

 gold ov silver, just as iron or nickel exhibits the magnetic force 

 with greater energy than platinum or chromium. Let two thin 

 bars, ab, cd, fig. 4, of two bodies of different diamagnetic powers 

 be placed at right angles to each other, so as to form a cross ; 

 let the cross be attached to the end of a lever and suspended 



