THE DYNAMO; WHAT IT DOES, AND HOW

Electricity compared to the heat and light of the Sun--The simple
dynamo--The amount of electric energy a dynamo will generate--The
modern dynamo--Measuring power in terms of electricity--The
volt--The ampere--The ohm--The watt and the kilowatt--Ohm's Law of
the electric circuit, and some examples of its application--Direct
current, and alternating current--Three types of direct-current
dynamos: series, shunt, and compound.

What a farmer really does in generating electricity from water that
would otherwise run to waste in his brook, is to install a private Sun
of his own--which is on duty not merely in daylight, but twenty-four
hours a day; a private Sun which is under such simple control that it
shines or provides heat and power, when and where wanted, simply by
touching a button.

This is not a mere fanciful statement. When you come to look into it
you find that electricity actually is the life-giving power of the
Sun's rays, so transformed that it can be handily conveyed from place
to place by means of wires, and controlled by mechanical devices as
simple as the spigot that drains a cask.

Nature has the habit of traveling in circles. Sometimes these circles
are so big that the part of them we see looks like a straight line,
but it is not. Even parallel lines, according to the mathematicians,
"meet in infinity." Take the instance of the water wheel which the
farmer has installed under the fall of his brook. The power which
turns the wheel has the strength of many horses. It is there in a
handy place for use, because the Sun brought it there. The Sun, by its
heat, lifted the water from sea-level, to the pond where we find
it--and we cannot get any more power out of this water by means of a
turbine using its pressure and momentum in falling, than the Sun
itself expended in raising the water against the force of gravity.

Once we have installed the wheel to change the energy of falling water
into mechanical power, the task of the dynamo is to turn this
mechanical power into another mode of motion--electricity. And the
task of electricity is to change this mode of motion back into the
original heat and light of the Sun--which started the circle in the
beginning.

Astronomers refer to the Sun as "he" and "him" and they spell his name
with a capital letter, to show that he occupies the center of our
small neighborhood of the universe at all ti