e 114, the magnet acts on twice as much of the wire at the same
time; so the current is stronger. If a very long piece of wire is used
and is looped around many times, and the whole coil is spun rapidly
between the poles of a powerful magnet, myriads of the electrons
in the wire rush around and around the loops--a powerful current of
electricity flows through the wire.

[Illustration: FIG. 115. The more loops there are, the stronger the
current.]

Now suppose you bring one loop of the long wire out, as shown in
Figure 115, and suppose you spin the rest of the loops between the
poles of the magnet. Then, to flow through the loops by the magnet the
electricity will have to go clear out through the long loop and back
again. While it is flowing through this long loop, we can make it
work. We can cut the long loop and attach one broken end to one part
of an electric lamp and the other end to the other part, so that the
electricity has to flow through the lamp in order to get back to the
spinning coil of wire, as shown in Figure 116. Such an arrangement as
this is really an extremely simple dynamo.

[Illustration: FIG. 116. If the electricity passes through a lamp on
its way around the circuit the filament of the lamp glows.]

[Illustration: FIG. 117. A dynamo in an electric light plant.]

You could make a dynamo that would actually work, by arranging such an
apparatus so that the coil would spin between the poles of the
magnet. But of course the big commercial dynamos are very much more
complicated in their construction. Figure 116 shows only the general
principle on which they work. The main point to note is that by
spinning a coil of wire between the poles of a magnet, you can make
electricity flow rapidly through the wire. And it is in this way that
most of the electricity we use is made.

The power spinning the coil of wire is sometimes steam, and sometimes
gasoline or distillate; and water power is very often used. A
large amount of our electricity comes from places where there are
waterfalls. Niagara, for instance, turns great dynamos and generates
an enormous amount of electricity.

WHY MANY AUTOMOBILES HAVE TO BE CRANKED. In an automobile, the magneto
is a little dynamo that makes the sparks which explode the gasoline.
While the automobile is going the engine spins the coil of wire
between the magnets, but at starting you have to spin the coil
yourself; and doing that is called "cranking" the automobile.
"Se