Fire-irons which have rested in an upright position in a room during
the summer months are often highly magnetic.
Iron bars standing erect, such as the gratings of a prison cell, or the
iron railings before houses, are often magnetic.
Great iron-clad ships are powerfully magnetic, and therefore affect
the compass by which the vessel is steered; ingenious arrangements are
therefore made to correct the effect of the local attraction, so that
the man-of-war may be steered correctly.
Magnetism may be made to pass through a deal board; to exhibit which,
lay a needle on the smooth part above, and run a magnet along the under
side, and the needle will be found to follow the course of the magnet.
A magnet dipped into boiling water loses part of its magnetism, which,
however, returns upon its cooling.
A sudden blow given to a magnet often destroys its magnetic power.