One of the most convenient uses to which electricity is put is in
producing motive power for driving all kinds of machines, from a
sewing-machine to a railway train, and we will now try to explain how
we can get this kind of work from electricity.
To begin with, you all know that a piece of machinery is usually made
to work by revolving a wheel which is part of the machine, either by
means of a steam-engine or by water-power, or, as a sewing-machine, by
foot-power. Now, when we work a piece of machinery by electricity we do
just the same thing by using, instead of the steam-engine or water or
foot power, an electric-engine called an "electromotor," which operates
in the same way--namely, by turning the wheel of the machine it is
applied to.
Foot-power is hard work for the person who is applying the power, and,
as you can easily see, one person can make only a very little power by
use of the feet. Steam and water power can be used for any large amount
of work, but the work must be within a few hundred feet of the engine
or the power cannot be used.
If there were a factory using steam-power a block or two away from
where you lived, and you had a lathe in your house which you would like
to have run by the steam-power in the factory, it would be practically
impossible to do this. Now, if the factory were still farther away from
your house, it would be still more impossible, and if it were a mile
away it would be foolish to dream of taking steam-power from a place so
far away.
Suppose, however, that this factory was lighted by electric lights,
it would be a very easy matter to take some of the power over to your
house. This could be done, even if the factory were miles away, by
taking two wires from their electric-light wires and running them
into your house to an electromotor connected with your lathe. This
electromotor would then run your lathe just as well as if it were
belted to a steam-engine.
So, you see, power can be carried in the form of electricity through
two wires over very great distances and made to do work at a long way
from the engine which is turning the dynamo to make the electricity.
Thus, you may have brought into your house wires which will give lights
and, at the same time, power to run a sewing-machine, a lathe, or any
other piece of machinery.
Having learned so far that a dynamo will make a continuous current of
electricity, and that two wires will carry this current to any place
where it is wanted, let us now see what takes place in the electromotor
to transform the electricity into power.
An electromotor (which we will now call by its short name, motor) is
simply a machine made like a dynamo. Curious as it may seem to you, it
is a fact that if you take two dynamo-machines exactly alike, and run
one with the steam-engine so as to produce electricity, and then take
the two main wires and attach them to the brushes of the other dynamo,
the electricity will drive this other dynamo so as to produce a great
deal of power which could be used for driving other machines. Thus, the
second dynamo would become a motor.
In the chapter on dynamos we explained something about the way they
were made and how the electricity was produced.