CHAP, ii.] ELECTRICITY AND MAGNETISM. 



79 



pole of the inducing magnet being of the opposite kind, 

 while the pole at the farther end of the bar is of the 

 same kind as the inducing pole. Magnetism can, how- 

 ever, only be induced in those bodies which we have 

 enumerated as magnetic bodies ; and those bodies in 

 which a magnetising force produces a high degree of 

 magnetisation are said to possess a high co- efficient 

 of magnetisation. It will be shown presently that 

 magnetic induction takes place along certain direc- 

 tions called lines of magnetic induction, or lines of 

 magnetic force, which may pass either through iron 

 and other magnetic media, or through air, vacuum, 



Fig- 45- 



glass, or other non-magnetic media : and, since induction 

 goes on most freely in bodies of high magnetic suscepti- 

 bility, those lines of force are sometimes (though not 

 too accurately) said to "pass by preference through 

 magnetic matter," or, that " magnetic matter conducts 

 the lines of force." 



Although magnetic induction takes place at a distance 

 across an intervening layer of air, glass, or vacuum, 

 there is no doubt that the intervening medium is directly 

 concerned in the transmission of the magnetic force, 

 though probably the true medium is the "aether" of 

 space surrounding the molecules of matter, not the 

 molecules themselves. 



