388 Royal Society. 



being simply proportional to the strength of the magnet, is propor- 

 tional to the square of the strength, which leads inevitably to the 

 conclusion that the body thus repelled contributes to the effect pro- 

 duced ; that its repulsion is due to an excited condition into which 

 it is thrown by the influencing magnet, the intensity of this excite- 

 ment varying within the limits already referred to, as the strength 

 of the magnet which produces it. This conclusion is further arrived 

 at by a close comparison of the repulsions of diamagnetic bodies 

 with the attraction of paramagnetic ones: both are found subservient 

 to one and the same law. 



It is next proved that the diamagnetic excitement produced by 

 one pole of a magnet is not the state which enables a pole of an op- 

 posite quality to repel the substance : — that each pole induces a con- 

 dition peculiar to itself, or, in other words, that the excitement of 

 diamagnetic bodies in the magnetic field is of a dual character. 



These points being established, a searching comparison is insti- 

 tuted between the phenomena exhibited by paramagnetic and dia- 

 magnetic bodies in three distinct cases : — first, when operated on 

 by the magnet alone ; secondly, when operated on by the current 

 alone ; and, thirdly, when operated on by the magnet and current 

 combined. A bar of iron was, in some of these cases, compared with 

 a bar of bismuth, but it was soon found necessary, in order to avoid 

 the proved errors of reasoning, to take strict account of the mole- 

 cular structure of the bismuth. A bar of this substance, cut in a 

 certain manner from the crystallized mass, exhibits between the 

 poles of a magnet precisely the same visible deportment as a bar of 

 iron, while it is well known that the normal deportment of bismuth 

 is opposed to that of iron. The author, in his examination of the 

 points before us, divided paramagnetic hars into two distinct classes, 

 and classified diamagnetic bars in the same manner ; one class he 

 called normal, and the other class abnormal, A normal paramagnetic 

 bar is one which sets its length from pole to pole in the magnetic 

 field, and a normal diamagnetic bar is one which sets its length at 

 right angles to the line joining the poles. An abnormal magnetic bar, 

 on the contrary, is one which sets its length equatorially ; while an 

 abnormal diamagnetic bar is one which sets its length axially. 



In all cases, whether operated on by the magnet alone, the cur- 

 rent alone, or the magnet and current combined, the deportment of 

 the normal paramagnetic bar is precisely antithetical to that of the 

 normal diamagnetic one. In the magnetic field the former sets 

 axially, the latter equatorially. Operated on by a voltaic current, the 

 former sets its length at right angles to the current, the latter sets 

 its length parallel to it. When magnet and current act together on 

 the bars, it is found that the disposition of forces which produces a 

 deflection from right to left of the paramagnetic bar produces a de- 

 flection from left to right of the diamagnetic bar. If the position 

 of equilibrium of the former be from N.E. to S.W., the position of 

 equilibrium of the latter is from N.W. to S.E. In short, the posi- 

 tion of rest for the normal magnetic bar is always at right angles to 

 the position of the diamagnetic bar. A precisely similar antithesis is 



