t 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 decomposition of the neutral fluid takes place. 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 anything 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 order, and to supply what is needed to render the
explanation complete. Do not quit the subject until you thoroughly
understand it; and if you are then able to look with your mind's eye
at the play of forces around a magnet, and see distinctly the
operation of those forces in the production of the magnetic curves,
the time which we have spent together will not have been spent in
vain.

FIG. 15.

In this thorough manner we must master our materials, reason upon
them, and, by determined study, attain to clearness of conception.
Facts thus dealt with exercise an expansive force upon the intellect;
they widen the mind to generalisation. We soon recognise a
brotherhood between the larger phenomena of Nature and the minute
effects which we have observed in our private chambers. Why, we
enquire, does the magnetic needle set north and south? Evidently it
is compelled to do so by the earth; the great globe which we inherit
is itself a magnet. Let us learn a little more about it. By means of
a bit of wax, or otherwise, attach the end of your silk fibre to the
middle point of your magnetic needle; the needle will thus be
uninterfered with by the paper loop, and will enjoy to some extent a
power of dipping' its point, or its eye, below the horizon. Lay your
bar magnet on a table, and hold the needle over the equator of the
magnet. The needle sets horizontal. Move it towards the north end of
the magnet; the south end of the needle dips, the dip augmenting as
you approach the north pole, over which the needle, if free to move,
will set itself exactly vertical. Move it back to the centre, it
resumes its horizontality; pass it on towards the south pole, its
north end now dips, and directly over the south pole the needle
becomes vertical, it