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A. LECTURE ON MAGNETISM. 369

opposite faces. How can this state of things 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, bot/2. its ends were attracted by your mag-
net; 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 hangfrom 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

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