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A LECTURE ON MAGNETISM. 373

middle of the magnet. Of course this is an imaginary case,
as you can never in reality thus detach your north mag-
netism from its neighbor. What is the action of the two
poles of the magnet on n .9 Your reply will of course be
that the pole S attracts 7?. while the pole N repels it.
Let the magnitude and direction of the attract-ion be ex-
pressed by the line 97. m, and the magnitude and direction
of the repulsion by the line 71. 0. Now the particle n being
equally distant from S and N, the line 7?. 0, expressing the
repulsion, will be equal to m n, which expresses the attrac-
tion, and the particle 92, acted upon by two such forces,
must evidently move in the direction 10 n, exactly midway
between m n and n 0. Hence you see that, although there
is no tendency of the particle 72 to move toward the mag-
netic equator, there is a tendency on its part to move
parallel to the magnet. If instead of a particle of north
magnetism we placed a particle of south magnetism op-
posite to the magnetic equator, it would evidently be urged
along the line n 9 ,° and if instead of two separate particles
of magnetism we place a little magnetic needle, containing
both north and south magnetism, opposite the magnetic
equator, its south pole being urged along 97. q, and its north
along 92 p, the little needle will be compelled to set itself
'parallel to the magnet S N. Make the experiment, and
satisfy yourselves that this is the case.

Substitute for your magnetic needle a bit of iron wire,
devoid of permanent magnetism, and it will set itself ex-
actly as the needle does. Acted upon by the magnet, the
wire, as you know, becomes a magnet and behaves as such ;
it will, of course, turn its north pole toward p, and south
pole toward 9, just like the needle.

But supposing you shift the position of your particle of
north magnetism, and bring it nearer to one end of your
magnet than to the other, the forces acting on the particle
are no longer equalg'the nearest pole of the magnet will

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