Bodies are repelled from the Poles of a Magnet. 169 



diamagnetic substances were next examined : they all acted in 

 the same manner as the wood, and thus showed that the cause 

 of the rotation lay, not in the structure of the substances, but 

 in the distribution of the magnetic force around them. This 

 distribution in fact was such, that the straight line which con- 

 nected the centre of one pole with that of the opposite one was 

 the line of weakest force. Ohm represents the distribution of 

 electricity upon the surfaces of conductors by regarding the 

 tensions as ordinates, and erecting them from the points to 

 which they correspond, the steepness of the curve formed by 

 uniting the ends of the ordinates being the measure of the 

 increase or diminution of tension. Taking the centre of the 

 magnetic field as the origin, and drawing lines axial and equa- 

 torial ; if we erect the magnetic tensions along these lines, we 

 shall find a steeper curve in the equatorial than in the axial 

 direction. This may be proved by suspending a bit of carbonate 

 of iron in the centre of the magnetic field; on exciting the 

 magnet, the suspended body will not move to the nearest portion 

 of the flat pole, though it may be not more than a quarter of 

 an inch distant, but will move equatorially towards the edges, 

 though they may be two inches distant. The little diamagnetic 

 bars referred to were therefore pushed into the axial position by 

 the force acting with superior power in an equatorial direction. 



The results just described are simply due to the recession of 

 the cuds of an elongated body from places of sti'onger to those 

 of weaker force ; but it is extremely instructive to observe how 

 this result is modified by structure. If, for example, a plate 

 of bismuth be suspended between the poles with the plane of 

 principal cleavage vertical, the plate will assert the equatorial 

 position from top to bottom ; and in the centre with almost the 

 same force as between the edges. The cause of this lies in the 

 structure of the bismuth. Its position in the field depends not 

 so much upon the distribution of the magnetic force around it, 

 as upon the direction of the force through it. I will not, however, 

 anticipate matters by entering further upon this subject at 

 present. 



IV. Comparative View of Paramagnetic and Diamagnetic 



PHyENOMENA. 



1 . State of Diamagnetic Bodies under Magnetic Influence. 



When a picc(> of soft iron is brought near to a magnet, it is 

 attracted by the latter : this attraction is not the act of the 

 magnet alone, but I'csults from the mutual action of the magnet 

 and the body upon which it operates. The soft iron in this 

 case is said to be magnetized by influence ; it becomes itself a 

 magnet, and the intensity of its magnetization varies with the 



Phil. Mag. S. 4. Vol. 10. No. (55. Sept, 1855. N 



