on the Polarity of the Diamagnetic Force. 171 



the position fig. 3, the poles NN' were attracted by the ends MP, 

 and the poles SS' repelled ; the ends n and o, therefore, acted as 

 two north poles, while the ends m and p acted as two south 

 poles. Now the direction of the current in the experiments re- 

 corded in the two tables referred to was that shown by the arrows 

 in fig. 4. Standing in front of the instrument, the direction in 

 the adjacent face of the spiral H'E' was from right to left, while 

 it was from left to right in HE. From this we may infer that 

 the polarity of the bismuth cylinders was the reverse of that 

 which would be excited in cylinders of iron under the same cir- 

 cumstances. The assertion however shall be transferred from 

 the domain of deduction to that of fact before we conclude. 



Let us now urge against these experiments all that ever has 

 been urged by the opponents of diamagnetic polarity. The bis- 

 muth cylinders are metallic conductors, and in moving them 

 through the spirals induced currents more or less powerful may 

 be excited in these conductors. The motion observed may not, 

 after all, be due to diamagnetic polarity, but to the currents thus 

 excited. I reply, that in all cases the number set down marks 

 the permanent position of rest of the magnets. Were the action 

 due to induced currents, these currents, being momentary, could 

 only impart a shock to the magnets, which, on the disappearance 

 of the currents, would return to their original position. But the 

 deflection is permanent, and is therefore due to an enduring cause. 

 In his paper on " Supposed Diamagnetic Polarity,^^ Mr. Earaday 

 rightly observes, — " If the polarity exists, it must be in the par- 

 ticles, and for the time permanent, and therefore distinguishable 

 from the momentary polarity of the mass due to induced tempo- 

 rary currents, and it must also be distinguishable from ordinary 

 magnetic polarity by its contrary direction.^^ These are the 

 precise characteristics of the force made manifest by the experi- 

 ments now under consideration. 



Further, the strength of induced currents depends on the con- 

 ducting power of the mass in which they are formed. Express- 

 ing the conducting power of bismuth by the number 1'8, that 

 of copper would be expressed by 73' 6*, the conductivity of the 

 latter being therefore forty times that of the former. Hence 

 the demand made by the opponents of diamagnetic polarity, to 

 have the experiments repeated with cylinders of copper ; for if 

 the eff'ect be due to induced currents, they will show themselves 

 in copper in a greatly increased degree. The following is the 

 result of a series of experiments made with two copper cylinders, 

 of the same dimensions as the bismuth ones already described. 



* Philosophical Magazine, Series 4, vol. vii. p. 37. 



