direction by the line n o, and the attraction by the shorter line
n M. The resultant of these two forces will be found by completing the
parallelogram m n o p, and drawing its diagonal n p. Along n p, then,
a particle of north magnetism would be urged by the simultaneous
action of S and N. Substituting a particle of south magnetism for n,
the same reasoning would lead to the conclusion that the particle
would be urged along it q. If we place at n a short magnetic needle,
its north pole will be urged along n p, its south pole along n q, the
only position possible to the needle, thus acted on, being along the
line p q, which is no longer parallel to the magnet. Verify this
deduction by actual experiment.

In this way we might go round the entire magnet; and, considering its
two poles as two centres from which the force emanates, we could, in
accordance with ordinary mechanical principles, assign a definite
direction to the magnetic needle at every particular place. And
substituting, as before, a bit of iron wire for the magnetic needle,
the positions of both will be the same.

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 that point. Go round and round the magnet; the direction of your
needle always coincides with the direction of the curve on which i