Bodies are repelled from the Poles of a Magnet. 287 



horizontally from the point ,v, before the flat or rounded pole N 

 of a magnet. Let the continuous line ah represent the needle 



Fi-. 4. 



□ 



of the powerful diamagnetic bod)^, and the 

 broken line cd that of the feeble one. On 

 the former a mechanical cou])lc acts in the 

 direction denoted by the arrows at its ends ; 

 and on the latter a couple operates in the 

 direction of the arrows at its ends. These 

 two couples are evidently opposed to each 

 other; but the former being, by hypothesis, 

 the more powerful of the two, it will over- 

 come the latter. The mechanical advantage 

 possessed by the attracted end a of the more 

 powerful bar, on account of its greater di- 

 stance from the axis of suspension x, will, in 

 an approximately uniform field of force which 

 we here assume, cause the centre of gravity 

 of the cross to move towards the pole N. 



In the formation of such a cross, howevei', 

 it is not necessary to resort to two different substances in order 

 to find two needles of different diamagnetic powers ; for in cry- 

 stallized bodies, or in bodies subjected to mechanical pressure, 

 the diamagnetic force acts with very different energies in differ- 

 ent directions. Let a mass of a diamagnetic body which has 

 been foi'cibly compressed in one direction be imagined; let two 

 needles be taken from such a mass, the one with its length 

 parallel, and the other with its length perpendicular to the line 

 of pressure. Two such needles, though composed of the same 

 chemical substance, will behave exactly as the two bars of the 

 cross in the experiment last described ; that needle whose lengtli 

 coincides with the line of ]iressurc will bear the same relation to 

 the other that the needle of the powerfully diamagnetic substance 

 bears to that of the feeble one. An inspection of the table at 

 page 282 will show that this must be the case. 



It is also shown in the following table, that in masses of cry- 

 stallized bismuth the diamagnetic repulsion acts with very difi'er- 

 ent energies in different directions. Cubes were taken from a 

 mass of bismuth with the planes of principal cleavage parallel 

 throughout to two opposite faces of each cube. The cubes were 

 placed upon the ends of a torsion balance, and the diamagnetic 

 repulsion was accurately measured when the force acted parallel 

 to the planes of cleavage. The cubes were then turned 90° 

 round, and the lepulsion was measured when the force acted 

 perpendicular to the planes referred to. 



