ELEMENTARY MAGNETISM. 355 



of each molecule. You have then a perfectly distinct 

 conception of the celebrated theory of magnetic fluids. 

 The strength of the magnetism excited is supposed to 

 be proportional to the quantity of neutral fluid decom- 

 posed. According to this theory nothing is actually 

 transferred from the exciting magnet to the excited 

 steel. The act of magnetisation consists in the forcible 

 separation of two fluids which existed in the steel before 

 it was magnetised, but which then neutralised each 

 other by their coalescence. And if you test your 

 magnet, after it has excited a hundred pieces of steel, 

 you will find that it has lost no force no more, in- 

 deed, than I should lose, had my words such a magnetic 

 influence on your minds as to excite in them a strong 

 resolve to study natural philosophy. I should rather 

 be the gainer by my own utterance, and by the reaction 

 of your fervour. The magnet also is the gainer by the 

 reaction of the body which it magnetises. 



Look now to your excited piece of steel; figure 

 each molecule with its opposed fluids spread over its 

 opposite faces. How can this state of things be per- 

 manent ? 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 neutralise 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 magnetised 

 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 permanent 

 magnets. It is manifest, indeed, that without coer- 



