244 Prof. Thomson on the Forces experienced by inductively 



sense in which the terms " attraction " and " repulsion " may 

 be applied to the action exerted by a magnet on a ferromag- 

 netic and a diamagnetic body respectively. A small sphere 

 of ferromagnetic substance, placed in the neighbourhood of 

 a magnet, experiences in general, a force ; but the term attrac- 

 tion, according to its derivation, means a force towards; and 

 if we apply it in any case, we must be able to supply an ob- 

 ject for the preposition. Now, in this case the force is towards 

 places of stronger "magnetic force;" and hence the action 

 experienced by a ferromagnetic ball may be called an attrac- 

 tion if we understand towards places of stronger force. Places 

 of stronger force are generally nearer the magnet than places 

 of weaker force, and hence small pieces of soft iron are ge- 

 nerally urged, on the whole, towards a magnet (in consequence 

 of which no doubt the term " attraction " came originally to 

 be applied) : but, as will be seen below, this is by no means 

 universally the case ; balls of soft iron being, in some cases, 

 actually repelled from the influencing magnet; and the term 

 " attraction " can only be universally used with reference to 

 ferromagnetic substances, on the understanding that it is 

 towards places of stronger force. The term " repulsion," the 

 reverse of " attraction," may, according to the same princi- 

 ples, be applied universally to indicate the force with which a 

 small diamagnetic sphere is urged towards places of weaker 

 force, or repelled from places of stronger force. 



6. The following passage, containing a statement of principles 

 on some of which Faraday himself lays much stress, but which 

 have not I think been sufficiently attended to by subsequent 

 experimenters, is quoted from the article in the Mathematical 

 Journal already referred to. 



7. "The result obtained above affords the true explanation 

 of the phenomenon observed by Faraday, that a thin bar or 

 needle of a diamagnetic substance, when suspended between 

 the poles of a magnet, assumes a position across the line 

 joining them. For 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 (as is the case, 

 for instance, with a bar of any ordinary dimensions, subject 

 only to the earth's influence), the direction it will assume, 

 when allowed to turn freely about its centre of gravity, will 

 be that of the lines of force, whether the material of which 

 it consists be diamagnetic, or magnetic matter such as soft 

 iron : but Faraday's result is due to the rapid decrease of 

 magnetic intensity round the poles of the magnet, and to the 

 length of the needle, which is considerable compared with the 



