PLUCKER ON THE THEORY OF DIAMAGNETISM. 335 



of yLt : »/, then when the induction in the bismuth excites a pole 

 of the same name, the repulsion will increase in the proportion 

 of V : fjL + v, When the induction is the opposite, the original 

 repulsion will only continue so long as /u, < v, that is, so long 

 as the induction of the spiral is smaller than the induction of 

 the magnet ; when this ceases to be the case the repulsion must 

 pass over into attraction. If the ratio /a : v in the case of the 

 diamagnetic induction of the bismuth does not differ too much 

 from the magnetic induction effected by the iron, then the 

 necessity that the above experiments must succeed becomes 

 manifest. 



If in the two spirals we introduce two cylinders of bismuth, 

 then it would follow theoretically that these two cylinders, when 

 the direction of the currents round both is the same, must 

 attract each other, inasmuch as the adjacent ends obtain opposite 

 polarities, exactly as would occur in the case of two cylinders 

 of iron, only the north pole would change with south pole and 

 south pole with north pole. When the directions of the cur- 

 rents in the spirals are opposed to each other, repulsion must 

 take place, for then the adjacent ends of the two cylinders 

 would obtain the same polarity. We can however state before- 

 hand, that in these two cases the attraction or repulsion is so 

 small that we can never hope to observe it by ordinary means. 

 And it is likewise evident that every experiment, no matter how 

 it may be made, to prove the mutual action of diamagnetic bars of 

 bismuth upon each other must be futile. Theoretic considera- 

 tions warn us not to vainly multiply such experiments to too 

 great an extent, nor to attach a false meaning to the negative 

 results by considering them as proofs against the theory. 



The attraction of the bismuth cylinders in the two spirals is 

 manifestly equal to the product of the magnetic excitation of 

 the two adjacent ends, and hence, retaining the numbers already 



asumed,-.^- 10,000 smaller than the corresponding repulsion 



between iron and bismuth. As this repulsion is already so 

 small, the attraction of the two induced bars of bismuth must 

 necessarily escape our powers of observation. 



If the latter attraction must be regarded as a magnitude of the 

 second order, then the repulsion of diamagnetic bismuth upon 



