d
in some form or other in every electrical industry.

The electric dynamo owes its being to those two discoveries. It consists
of coils of copper wire wound on a shaft, and that shaft is revolved
close to a powerful magnet. The influence of the magnet causes electric
currents to be produced in the coils of copper wire, and these currents
are delivered by the coils into suitable conductors or wires by means of
which the currents are led to the place where they have to do their
work. One very interesting thing about the modern dynamo machine is that
it is what electrical men call "self-exciting." That does not mean that
it gets into a state of excitement about itself. It means that the
dynamo provides its own magnetism. At first dynamos were made with great
big steel magnets, but those were very expensive and unsatisfactory.
Then a clever inventor hit upon the plan of using electro-magnets, and
sending part of the current of the dynamo through their coils to give
them magnetism. This is the action of the self-exciting dynamo. When the
collection of coils wound on the revolving shaft first begins to turn,
very little current is produced, because there is very little magnetism
in the iron magnets. Part of this current goes through the magnet coils
and increases the magnetism; this strengthens the current in the coils,
and this process goes on until, after a few minutes, the magnets are
fully magnetized and the coils are giving their full strength of
current.

[Illustration: Diagram showing the electric circuit through each car,
and illustrating the method of sending more than one car along the same
wire.]

Some time after this was discovered, it became known that if the two
wires from a dynamo were joined to a second dynamo instead of to an
electric lamp, this second dynamo would revolve, and could be used to
drive a machine, such as a sewing-machine or a printing-press.

At first this electric motor, as it was called, was used only for
turning wheels that were stationary, but it was soon seen that there was
good work for it to do in turning wheels that should travel along over
the ground. Then began the electric railway.

Having got your electric motor it would seem a comparatively easy job to
mount it on a car, to fix up a moving connection with an electric wire,
and to make the motor turn the car-wheels. It looks easy enough to-day
in places where hundreds of horseless cars are running about in all
directions as i