Bodies are repelled from the Poles of a Magnet. 277 



massive, some in a state of powder, but iu no single instance 

 have I discovered an exception to the law that the line of com- 

 pression of purely diamagnetic bodies is the line of strongest 

 diamagnetization. The approximation of diamagnetic particles 

 is therefore accompanied by an augmentation of their power, 

 instead of a diminution of it, as supposed by the theory of M. 

 Weber. 



Any hypothesis which involves the idea of the diminution of 

 the diamagnetic action of a body by the approximation of its 

 particles, is, I believe, opposed to facts. Such a hypothesis 

 must, I imagine, form the basis of the following remark of Prof. 

 W. Thomson : — referring to "a thin bar or needle of a diamag- 

 netic substance," he says, " such a needle has no tendency to 

 arrange itself across the lines of magnetic force ; but, as will be 

 shown in a future paper, if it be very small compared with the 

 dimensions and distance of the magnet, the direction it will 

 assume, when allowed to turn freely round its centre of gravity, 

 will be that of the lines of force*." I have not found in any 

 of the subsequent numbers of the Philosophical Magazine the 

 proof here promisedf. But I doubt not the conclusion involves 

 the assumption that the mutual action of diamagnetic particles 

 is to weaken each other, and hence to produce a more feeble mag- 

 netization along a thin diamagnetic bar than across it — an assump- 

 tion which, as already shown, is contradicted by experiment. 



It is scarcely possible to reflect upon the discovery of Faraday 

 in all its bearings, without being deeply impressed with the feel- 

 ing that we know absolutely nothing of the physical causes of 

 magnetic action. We find the magnetic force producing, by 

 processes which are evidently similar, two great classes of effects. 

 We have a certain number of bodies which are attracted by the 

 magnet, and a far greater number which are repelled by the 

 same agent. Supposing these facts to have been known to 

 Ampere, would he have satisfied his profound mind by founding 

 a theoi-y which accounts for only the smaller portion of them ? 

 This theory is admirable as far as it goes, but the generalization 

 is yet to come which shall show the true relationship of phteno- 

 mena, towards whose connexion the theory of Ampere furnishes 

 at presi-nt no apparent clue. 



Royal Institution, October 1854. 



* Phil. Mag. vol. xxxvii. p. 2-14. 



t This remark apj^ears to have induced Mr. Thomson to publish the 

 proof referred to in the last Number of the Philosophical Magazine. The 

 arguments there brought forward have been long familiar to me, but I 

 regret to say that I cannot attach nuich real value to them. At some 

 future day I hope to be able to justify the scepticism which I here venture 

 to express.— J. T., May 5, 1855. 



