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 times.
Magnets and Magnetism
The dynamo is a mechanical engine, like the steam engine, the water turbine or the gas engine; and it converts the mechanical motion of the driven wheel into electrical motion, with the aid of a magnet. Many scientists say that the full circle of energy that keeps the world spinning, grows crops, and paints the sky with the Aurora Borealis, begins and ends with magnetism—that the sun's rays are magnetic rays. Magnetism is the force that keeps the compass needle pointing north and south. Take a steel rod and hold it along the north and south line, slightly inclined towards the earth, and strike it a sharp blow with a hammer, and it becomes a magnet—feeble, it is true, but still a magnet.
Take a wire connected with a common dry battery and hold a compass needle under it and the needle will immediately turn around and point directly across the wire, showing that the wire possesses magnetism encircling it in invisible lines, stronger than the magnetism of the earth.