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.
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