tlie Absurdity of Diamagnetic Polarity. 193 



and shall avoid unnecessary references to the physical theories 

 of magnetism. 



To begin, the property which distinguishes the so-called 

 diamagnetic bodies (like bismuth and copper) from the other, 

 or paramagnetic bodies (like iron), is shown 

 by the following classical experiment. A Fig. 1. 



small bar, A, of the substance to be experi- 

 mented on, is hung by a thread between the 

 poles, NS, of a powerful electromagnet and 

 then the magnet is excited. If the bar A be 

 one of the so-called diamagnetic substances, 

 it will set its length at right angles to the N 

 line joining the two poles of the electro- _J ' ' ' LiL 

 magnet, as shown in the second accompany- 

 ing figure, which is supposed to be a view as 

 seen by an eye looking from above. If, however, the bar A 

 be one of the paramagnetic substances, it sets its length 

 along the line joining the two poles of the 

 electromagnet, IV. 9. 



Instead of taking the above fundamental 

 experiment as our starting-point, I prefer, ^ -"- 1 rg~ 

 for the sake of simplicity, to take another — LI 

 which is easier to understand. The second 

 experiment has not yet been performed ; but it is admissible 

 to make it the basis of our discussion, for not only is it equiva- 

 lent to the classical experiment described above, but the 

 inferences drawn from both will be the same. 



In our ideal experiment, we take a powerful electromagnet 

 whose poles are at a considerable distance apart, and hang a 

 small piece, M, of the substance to be 

 tested by a thread near either pole, P, of Fig. 3. 



the electromagnet. Then on exciting 

 the magnet, it is found that if M be a 

 piece of iron, it is drawn nearer the 



pole P, while if it be a piece of bismuth, » JL 



it would be driven further away from it. I ^-M- 



The so-called explanation which is 

 usually given of these phenomena may be divided into two 

 parts : — 



(a) It is supposed (that is, assumed) that the pressure of 

 the air is strictly uniform all over the surface of M, from 

 which it would follow that the pressure of the air can have 

 no influence in causing the body IVI to approach or recede 

 from the excited pole P. 



(b) It is then supposed, as a necessary consequence, that 

 when the electromagnet is excited, a piece of iron is attracted 

 to the pole P, and tbat a piece of bismuth is repelled. 



FhiL May. S. 5. Vol. 32. 2To. 195. August 1891. 



