Bodies are repelled from the Poles of a Magnet. 177 



Here we find experiment in strict accordance with the theo- 

 retical deduction stated at the commencement of the present 

 chapter. The intensity of the magnetism of the steel needle is 

 constant, for the steel resists magnetization by influence; the 

 consequence is that the attraction is simply proportional to the 

 strength of the magnet. 



A consideration of the evidence thus adduced from indepen- 

 dent sources, and obtained by different methods^ must, I imagine, 

 render the conclusion certain that diamagnetic bodies, like mag- 

 netic ones, exhibit their phfeuomena in virtue of a state of mag- 

 netization induced in them by the influencing magnet. This 

 conclusion is in no way invalidated by the recent researches of 

 M. Pliickei-, on the law of induction in paramagnetic and dia- 

 magnetic bodies, but, on the contrary, derives support from his 

 experiments. With current strengths which stand in the ratio 

 of 1 : 2, M. Pliicker finds the repulsion of bismuth to be as 

 1 : 3'63, M'hich, though it falls short of the ratio of 1 : 4, as the 

 law of increase according to the square of the current would have 

 it, is sufficient to show that the bismuth was not passive, but 

 acted the part of an induced diamagnet in the experiments. In 

 the case of the soft iron itself, M. Pliicker finds a far greater 

 divergence ; for here currents which stand in the ratio of 1 : 2 

 produce attractions only in the ratio of 1 : 2" 76. 



2. Duality of Diamagnetic Excitement. 



Having thus safely established the fact that diamagnetic 

 bodies are repelled, in virtue of a certain state into which they 

 are cast by the influencing magnet, the next step of our inquiry 

 is ; — Will the state evoked by one magnetic pole facilitate, or 

 prevent, the repulsion of the diamagnetic body by a second pole 

 of an opposite quality ? If the force of repulsion were an action 

 on the mass, considered as ordinary matter, this mass, being 

 repelled by both the north and the south pole of a magnet, when 

 they operate upon it separately, ought to be repelled by the sum 

 of the forces of the two poles where they act upon it together. 

 But if the excitation of diamagnetic bodies be of a dual nature, 

 as is the case with the magnetic bodies, then it may be expected 

 that the state excited by one pole will not facilitate, but on the 

 contrary prevent, the repulsion of the mass by a second opposite 

 pole. 



To solve this question the ajiparatus sketched in fig. 5a. 

 Plate IV. was made use of. AB and CD are two helices of cop- 

 per wire 12 inches long, of 2 inches internal, and of 5i inches 

 external diameter. Into them fit soft iron cores 2 incht"s thick : 

 the cores are bent as in the figure, and reduced to flat surfaces 



