Kay Bergman, age 11, of Spokane, Wash., for her question:

How does electricity flow?

Mankind learned to use fire before the dawn of history. But he did not know what it was or how it worked. He wondered about it while he used and controlled it through countless generations. But not until the modern age of Science did man learn the nature of fire and how it works.

Electricity was also discovered and put to use before anyone understood what it was. The first experiments with electric current were rated as parlor tricks. The first electric battery was a pile of metal discs sandwiched between brine soaked paper. The small current was led to and from the battery by a circuit of copper wire. When the circuit was closed, a mysterious electric current charged the copper wire. It stopped when the circuit was opened or broken.

This tiny battery seemed no use at all. But man soon began to realize that he had tapped a mighty force of nature. The powerful force of electricity loomed as a tremendous titan. A certain jolt, later called voltage, would send this mighty force into a circuit of copper wire. All that was needed to got more power was to create bigger circuits and more voltage.

This problem was solved when the dynamo was invented. It was known that an electric current is related to magnetism. An electric current acts like a magnet. With the dynamo, magnetism was used to create voltage, plenty of voltage. This ended the limits of the small battery.

Bigger and better dynamos were made. Miles of copper wire carried electric current to light cities and soon to run machinery. But still we did not know what made the miracle happen. We knew that voltage caused current in the circuit and we know how to make it work. But no one was sure what happened‑inside the copper wire carrying the current.

Part of this mystery was solved in 1909 by Dr. R.A. Millikan, the great American scientist. Dr. Millikan showed that an electric current was paused by electrons within the copper. Electrons are atomic particles of negative electricity. F"_ h popper atom has 29 of ten arranged in shells about its nucleus.

The inside shell of the copper atom is complete with two electrons. The second is complete with eight and the third with 18 electrons. This leaves one lone electron in the outside fourth shell. For same mysterious reason, the jolt of voltage jogs this lone electron. When voltage is applied to a circuit, countless numbers of these 29ers are jolted. This is the energy which makes an electric current.

In direct current, the electrons move in one direction only. In alternating current, they move together forward than backwards. The electrons in a normal house current move back and forth 60 times a second. To light an ordinary bulb, three billion billion electrons must dance back and forth 60 times every second.

Electric current, then, is caused by moving electrons. They are pus had by voltage from a generator or dynamo. To make a current, there must be an unbroken circuit of wire to and from the generator. We know how to make this trick work, but we still do not know why the voltage power makes the electrons move.