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