maximum; but all the lower half of the magnet, from E to S (fig. 22),
attracts one end of the needle, while all the upper half, from E to N,
attracts the opposite end. This _doubleness_ of the magnetic force is
called _polarity_, and the points near the ends of the magnet in which
the forces seem concentrated are called its _poles_.

[Illustration: Fig. 22.]

What, then, will occur if we break this magnet in two at the centre E?
Shall we obtain two magnets, each with a single pole? No; each half is
in itself a perfect magnet, possessing two poles. This may be proved
by breaking something of less value than the magnet--the steel of a
lady's stays, for example, hardened and magnetized. It acts like the
magnet. When broken, each half acts like the whole; and when these
parts are again broken, we have still the perfect magnet, possessing,
as in the first instance, two poles. Push your breaking to its utmost
sensible limit--you cannot stop there. The bias derived from
observation will infallibly carry you beyond the bourne of the senses,
and compel you to regard this thing that we call magnetic polarity as
resident in the ultimate particles of the steel. You come to the
conclusion that each molecule of the magnet is endowed with this polar
force.

Like all other forces, this force of magnetism is amenable to
mechanical laws; and, knowing the direction and magnitude of the
force, we can predict its action. Placing a small magnetic needle near
a bar magnet, it takes a determinate position. That position might be
deduced theoretically from the mutual action of the poles. Moving the
needle round the magnet, for each point of the surrounding space there
is a definite direction of the needle and no other. A needle of iron