he same conditions. There is no more
attraction than repulsion. If we seal one magnet up in a paper or a
box, and then suspend another over the box, the north pole of the one
outside will tend to the south pole of the one in the box, and vice
versa.

Our next discovery is, that whenever a magnet attracts a piece of iron
it makes that iron into a magnet, at least for the time being. In the
case of ordinary soft or untempered iron the magnetism disappears
instantly when the magnet is removed. But if the magnet be made to
attract a piece of hardened steel, the latter will retain the magnetism
produced in it and become itself a permanent magnet.

This fact must have been known from the time that the compass came into
use. To make this instrument it was necessary to magnetize a small bar
or needle by passing a natural magnet over it.

In our times the magnetization is effected by an electric current. The
latter has curious magnetic properties; a magnetic needle brought
alongside of it will be found placing itself at right angles to the
wire bearing the current. On this principle is made the galvanometer
for measuring the intensity of a current. Moreover, if a piece of wire
is coiled round a bar of steel, and a powerful electric current pass
through the coil, the bar will become a magnet.

Another curious property of magnetism is that we cannot develop north
magnetism in a bar without developing south magnetism at the same time.
If it were otherwise, important consequences would result. A separate
north pole of a magnet would, if attached to a floating object and
thrown into the ocean, start on a journey towards the north all by
itself. A possible method of bringing this result about may suggest
itself. Let us take an ordinary bar magnet, with a pole at each end,
and break it in the middle; then would not the north end be all ready
to start on its voyage north, and the south end to make its way south?
But, alas! when this experiment is tried it is found that a south pole
instantly 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