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A LECTURE ON MAGNETISM. 375

Now, I think, Without further preface, you will be able
to comprehend for yourselves, and explain to others, one
of the most interesting effects in the whole domain of
magnetism. Iron filings you know are particles of iron,
irregular in shape, being longer in some directions than in
others. For the present experiment, moreover, instead of
the iron filings, very small scraps of thin iron wire might be
employed. I place a sheet of paper over the magnet; it is
all the better if the paper be stretched on a wooden frame,
as this enables us to keep it quite level. I scatter the
filings, or the scraps of wire, from a sieve upon the paper,
and tap the latter gently, so as to liberate the particles for
a moment from its friction. The magnet acts on the filings
through the paper, and see how it arranges them! They
embrace the magnet in a series of beautiful curves, which
are technically called magnetic curves, or lines of magnetic
force. Does the meaning of these lines yet flash upon
you ? Set your magnetic needle or your suspended bit of
wire at any point of one of the curves, and you will find
the direction of the needle or of the wire to be exactly that
of the particle of iron, or of the magnetic curve at the
point. Go round and round the magnet; the direction of
your needle always coincides with the direction of the curve
on which it is placed. These, then, are the lines along
which a particle of south magnetism, if you could detach it,
WOuld move to the north pole, and a bit of north magnetism
to the south pole; they are the lines along which the de-
composition of the neutral fluid takes place, and in the case
of the magnetic needle, one of its poles being urged in one
direction, and the other pole in the opposite direction, the
needle must necessarily set itself as a tangent to the curve.
I will not seek to simplify this subject further. If there
be any thing obscure or confused or incomplete in my
statement, you ought now, by patient thought, to be able
to clear away the obscurity, to reduce the confusion to

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