CHAP, ii.] ELECTRICITY AND MAGNETISM. 89 



poles, the other only S. poles. This would be true no 

 matter how small the individual particles. 



If the intrinsic magnetisation of the steel at every 

 part of a magnet were equal, the free poles would be 

 found only at the ends ; but the fact that the free mag- 

 netism is not at the ends merely, but diminishes from 

 the ends towards the middle, shows that the intensity of 

 the intrinsic magnetisation must be less towards and at 

 the ends than it is at the middle of the bar. 



107. Lamellar Distribution of Magnetism. 

 Magnetic Shells. Up to this point the ordinary 

 distribution of magnetism along a bar has been the only 

 distribution considered. But it is possible to have 

 magnetism distributed over a thin sheet so that the 

 whole of one face of the sheet shall have one kind of 

 magnetism, and the other face the other kind of magnet- 

 ism. If an immense number of little magnets were 

 placed together side by side, like the cells in a honey 

 comb, all with their N. -seeking ends upwards, and S.- 

 seeking ends downwards, the whole of one face of the 

 slab would be one large flat N. -seeking pole, and the 

 other face S. -seeking. Such a distribution as this over a 

 surface or sheet is termed a lamellar distribution, to 

 distinguish it from the ordinary distribution along a line 

 or bar, which is termed, for distinction, the solenoidal 

 distribution. A lamellarly magnetised magnet is some- 

 times spoken of as a magnetic shell. The properties 

 of magnetic shells are extremely important on account of 

 their analogy with those of closed voltaic circuits. 



108. Magnetic Figures. Gilbert showed 1 that if 

 a sheet of paper or card be placed over a magnet, and 

 iron-filings are dusted over the paper, they settle down 

 in curving lines, forming a magnetic figure, the general 

 form of which is shown in Fig. 50. The filings should 

 be fine, and sifted through a bit of muslin ; to facilitate 

 their settling in the lines, the sheet of paper should be 



1 The magnetic figures were known to Lucretius. 



