A LECTURE ON MAGNETISM. 369 



opposite faces. How can this state of tilings be perma- 

 nent ? The fluids, by hypothesis, attract each other ; 

 what, then, keeps them apart ? Why do they not instantly 

 rush together across the equator of the atom, and thus neu- 

 tralize each other ? To meet this question, philosophers 

 have been obliged to infer the existence of a special force 

 which holds the fluids asunder. They call it coercive 

 force and it is found that those kinds of steel which offer 

 most resistance to being magnetized, which require the 

 greatest amount of coercion to tear their fluids asunder, 

 are the very ones which offer the greatest resistance to the 

 reunion of the fluids after they have been once separated. 

 Such kinds of steel are most suited to the formation of per- 

 manent magnets. It is manifest, indeed, that without 

 coercive force a permanent magnet -would not be at all pos- 

 sible. 



You have not forgotten that, previous to magnetizing your 

 darning-needle, both its ends were attracted by your mag- 

 net 5 and that both ends of your bit of iron wire were acted 

 upon in the same way. Probably also long before this you 

 will have dipped the end of your magnet among iron filings, 

 and observed how they cling to it, or into a nail-box, and 

 found how it drags the nails after it. I know very well 

 that if you are not the slaves of routine, you will have by 

 this time done many things that I have not told you to do, 

 and thus multiplied your experience beyond what I have 

 indicated. You are almost sure to have caused a bit of 

 iron to hang from the end of your magnet, and you have 

 probably succeeded in causing a second piece to attach 

 itself to the first, a third to the second ; until finally the 

 force has become too feeble to bear the weight of more. 

 If you have operated with nails, you may have observed 

 that the points and edges hold together with the greatest 

 tenacity ; and that a bit of iron clings more firmly to the 

 corner of your magnet than to one of its flat surfaces. In 



