develops itself on one side of the break, and a north pole on the
other side, so that the two pieces will simply form two magnets,
each with its north and south pole. There is no possibility of
making a magnet with only one pole.

It was formerly supposed that the central portions of the earth
consisted of an immense magnet directed north and south. Although
this view is found, for reasons which need not be set forth in
detail, to be untenable, it gives us a good general idea of the
nature of terrestrial magnetism. One result that follows from the
law of poles already mentioned is that the magnetism which seems
to belong to the north pole of the earth is what we call south on
the magnet, and vice versa.

Careful experiment shows us that the region around every magnet is
filled with magnetic force, strongest near the poles of the
magnet, but diminishing as the inverse square of the distance from
the pole. This force, at each point, acts along a certain line,
called a line of force. These lines are very prettily shown by the
familiar experiment of placing a sheet of paper over a magnet, and
then scattering iron filings on the surface of the paper. It will
be noticed that the filings arrange themselves along a series of
curved lines, diverging in every direction from each pole, but
always passing from one pole to the other. It is a universal law
that whenever a magnet is brought into a region where this force
acts, it is attracted into such a position that it shall have the
same direction as the lines of force. Its north pole will take the
direction of the curve leading to the south pole of the other
magnet, and its south pole the opposite one.