the
bolts to be put in. These bolts are the magnet cores (K), 6 inches long,
but they may be even longer, if you bore several holes (N) through the
bench so you may set over the tailpiece.

With a single tool made substantially like this, over a thousand of the
finest magnets have been wound. Its value will be appreciated after you
have had the experience of winding a few magnets.

ORDER IN THE WORKSHOP.--Select a place for each tool on the rear upright
of the bench, and make it a rule to put each tool back into its place
after using. This, if persisted in, will soon become a habit, and will
save you hours of time. Hunting for tools is the unprofitable part of
any work.

CHAPTER III

MAGNETS, COILS, ARMATURES, ETC.

THE TWO KINDS OF MAGNET.--Generally speaking, magnets are of two kinds,
namely, permanent and electro-magnetic.

PERMANENT MAGNETS.--A permanent magnet is a piece of steel in which an
electric force is exerted at all times. An electro-magnet is a piece of
iron which is magnetized by a winding of wire, and the magnet is
energized only while a current of electricity is passing through the
wire.

ELECTRO-MAGNET.--The electro-magnet, therefore, is the more useful,
because the pull of the magnet can be controlled by the current which
actuates it.

The electro-magnet is the most essential of all contrivances in the
operation and use of electricity. It is the piece of mechanism which
does the physical work of almost every electrical apparatus or machine.
It is the device which has the power to convert the unseen electric
current into motion which may be observed by the human eye. Without it
electricity would be a useless agent to man.

While the electro-magnet is, therefore, the form of device which is
almost wholly used, it is necessary, first, to understand the principles
of the permanent magnet.

MAGNETISM.--The curious force exerted by a magnet is called magnetism,
but its origin has never been explained. We know its manifestations
only, and laws have been formulated to explain its various phases; how
to make it more or less intense; how to make its pull more effective;
the shape and form of the magnet and the material most useful in its
construction.

[Illustration: _Fig 5._ PLAIN MAGNET BAR]

MATERIALS FOR MAGNETS.--Iron and steel are the best materials for
magnets. Some metals are non-magnetic, this applying to iron if combined
with manganese. Others, like sulphur, zinc, bismuth, an