strip of steel. Hold the
strip upright in your left hand, and cause the test-needle to approach
the lower end of your strip; one end of the test-needle is attracted,
the other is repelled. Raise your needle along the strip; its
oscillations, which at first were quick, become slower; opposite the
middle of the strip they cease entirely; neither end of the needle is
attracted; above the middle the test-needle turns suddenly round, its
other end being now attracted. Go through the experiment thoroughly:
you thus learn that the entire lower half of the strip attracts one
end of the needle, while the entire upper half attracts the opposite
end. Supposing the north end of your little needle to be that
attracted below, you infer that the entire lower half of your
magnetised strip exhibits south magnetism, while the entire upper half
exhibits north magnetism. So far, then, you have determined the
distribution of magnetism in your strip of steel.

You look at this fact, you think of it; in its suggestiveness the
value of an experiment chiefly consists. The thought naturally
arises: 'What will occur if I break my strip of steel across in the
middle? Shall I obtain two magnets each possessing a single pole?'
Try the experiment; break your strip of steel, and test each half as
you tested the whole. The mere presentation of its two ends in
succession to your test-needle, suffices to show that you have _not_ a
magnet with a single pole--that each half possesses two poles with a
neutral point between them. And if you again break the half into two
other halves, you will find that each quarter of the original strip
exhibits precisely the same magnetic distribution as the whole strip.
You may continue the breaking process: no matter how small your
fragment may be, it still possesses two opposite poles and a neutral
point between them. Well, your hand ceases to break where breaking
becomes a mechanical impossibility; but does the mind stop there? No:
you follow the breaking process in idea when you can no longer realise
it in fact; your thoughts wander amid the very atoms of your steel,
and you conclude that each atom is a magnet, and that the force
exerted by the strip of steel is the mere summation, or resultant, of
the forces of its ultimate particles.

Here, then, is an exhibition of power which we can call forth at
pleasure or cause to disappear. We magnetise our strip, of steel by
drawing it along the pole of a magnet;