136 Relation of Diamagnetic Polarity to Magnecrystallic Action. 



in favour of this polarity to that already furnished in such 

 abundance. 



Perhaps as remarkable an illustration as could be chosen of 

 the apparently perplexing character of certain magnetic phseno- 

 niena, but of their real simplicity when the exact nature of the 

 force producing them is understood, is furnished by the follow- 

 ing experiment. I took a quantity of pure bismuth powder and 

 squeezed it between two clean copper plates until the powder 

 became a compact mass. A fragment of the mass suspended 

 before the pointed pole of a magnet was forcibly repelled ; and 

 when suspended in the magnetic field with the direction of 

 pressure horizontal, in accordance with results already suffi- 

 ciently well known, it set its line of pressure equatorial. 



A second quantity of the bismuth powder was taken, and with 

 it was mixed a quantity of powdered carbonate of iron, amount- 

 ing to x^ths per cent, of the whole ; the mass was still strongly 

 diamagnetic, but the line of compression, instead of setting 

 equatorial, as in the former instance, set decidedly axial. 



A quantity of the mixed powder was next taken, in which the 

 magnetic constituents amounted to 1 per cent. The mass was 

 still diamagnetic, but the line of compression set axial; it did so 

 when the influence of exterior form was quite neutralized, so 

 that the eff"ect must be referred solely to the compression of 

 the mass. With 2 per cent, of carbonate of iron powder the 

 mass was magnetic, and set with increased energy its line of 

 compression axial; with 4 per cent, of carbonate of iron the 

 same effect was produced in a still more exalted degree. 



Now, why should the addition of a quantity of carbonate of 

 iron powder, which is altogether insufficient to convert the mass 

 from a diamagnetic to a paramagnetic one, be able to overturn 

 the tendency of the diamagnetic body to set its line of com- 

 pression equatorial ? The question is puzzling at first sight, 

 but the difiiculty vanishes on reflection. The repulsion of the 

 mass of bismuth, suspended before a pointed pole, depends 

 upon the general capacity of the mass for diamagnetic induction, 

 while its position as a magnecrystal between the flat poles de- 

 pends on the difference between its capacities in two difterent 

 directions. The diamagnetic capacity of the mass may be verj'^ 

 great,- while its capacity in different directions may be nearly 

 alike, or quite so : the former, in the case before us, came into 

 play before the pointed pole ; but between the flat poles, where 

 the directive, and not the translative energy is great, the car- 

 bonate of iron powder, whose directive power, when compressed, 

 far exceeds that of bismuth, determined the position of the 

 body. In this simple way a number of perplexing results ob- 

 tained with bodies formed of a mixture of paramagnetic and 



