Read an Excerpt
The Story of Electricity
With 20 Easy-to-Perform Experiments
By George deLucenay Leon
Dover Publications, Inc.Copyright © 1983 George deLucenay Leon
All rights reserved.
A Stactic Attraction
Early humans were astounded by four distinct wonders that we now know to be electrical:
2. The way amber attracted light objects.
3. "St. Elmo's Fire"—a glow or a flame sometimes seen on the tips of masts during stormy weather. (St. Elmo was the patron saint of sailors.)
4. The way certain fishes, such as the electric eel and the torpedo-fish, stunned their prey.
Originally, many of these phenomena were explained by myths. For example, the Vikings believed that Thor, the god of thunder, owned a magic hammer. He would hurl it down to earth, creating lightning as it spun down. The Dutch settlers up the Hudson River invented a humorous folk tale in which thunder was caused by the gods of the nearby hills who were knocking down pins in a bowling game.
Not until the eighteenth century was it realized that lightning was indeed electricity—millions of volts being discharged from one cloud to another or from a cloud to earth.
Electricity began to be recognized for what it was less than 300 years ago. Magnetism, on the other hand—or what was thought to be magnetism—has been studied for about 2,600 years. It was this study that led to the discovery of how to generate electricity.
Electricity does not naturally exist in quantities that we can control and use for our benefit. There is no rock, no liquid, no kind of air that gives us electricity directly. We can generate electricity from the sun, from waterfalls, from coal and oil, but only after many intermediary steps.
Over the centuries, many men experimented with electricity and magnetism. They developed theories and tested them with experiments. From the results, they could tell if they were on the right track. They would then develop further theories and make another little stride along the road of knowledge.
Using this book, you will be able to understand these men's thoughts by repeating their experiments.
(Weren't there any women studying magnetism and electricity? Unfortunately, for centuries women were not allowed to study science. It was considered exclusively a man's subject. It was not until 1911, when Marie Curie won a Nobel prize in chemistry, that women came to be recognized as significant contributors in the area of science.)
Thales "Discovers" Static Electricity
To begin with, we must travel backward in time to Greece in the seventh century B.C.—almost 2,600 years ago. The place is Miletus, an ancient city on the west coast of Asia Minor, where a famous philosopher and mathematician named Thales lived. He lived from 640 to 546 B.C. and was the first person to have recorded interesting things about static electricity and magnetism. There were probably people before Thales who were aware of static electricity and magnetism as curiosities, but they left no writings to tell us about their experiments.)
Thales found that amber will attract light objects such as feathers, bits of dried grass, and straw. We can only guess at the events that led to his discovery. One day, Thales was perhaps polishing some amber with a piece of fur or wool. To his surprise, when he laid the stone near a straw, it jumped and clung to the amber. Curious, he wanted to see what amber would do to other light objects. Feathers and dozens of other objects were tried. The results were the same. The light objects fastened themselves onto the amber.
He repeated the experiment, but this time without rubbing the amber. Nothing happened. Again he rubbed the amber, and again the feather and other objects responded. He must have repeated his experiments countless times to make certain that what he was observing was not just lucky chance. Eventually, Thales came to the conclusion that it was his rubbing that made amber "magnetic." (Actually, as you will see in awhile, rubbing the amber created a static electric charge and not magnetism.) You can duplicate Thales' experiments in Experiment No. 1.
Every good experimenter repeats his experiments several times. To be of value, the results must be the same each time.
Thales noticed that while rubbed amber attracted light objects, it did not attract metal. But when he picked up a piece of lodestone (an iron ore with a silvery finish, also called magnetite), he found he could attract pieces of iron. He also noted that lodestone attracts iron without being rubbed.
Later, other experimenters found that a variety of substances, such as diamonds, were able to attract the same way that amber did. Such substances we now call insulators. They do not conduct electricity. The rubber around an electric cord is one example of an insulator. It prevents electricity from escaping from the wire to anything near the wire. On the other hand, lots of substances do not attract metals, paper, feathers, or anything else, no matter how long you rub. We call these substances conductors. A conductor is able to allow electricity to flow through it. Examples of conductors are copper, silver, or gold wire.
Until the seventeenth century, it was believed that rubbed amber and magnets such as the lodestone had one thing in common—the ability to attract other objects. The explanation then was that magnets and amber did something to the air around them, and this was what caused the attraction. No difference was found between the action of the amber and the lodestone.
Walk across a nylon or wool rug on a cold dry day. Now touch a doorknob, or any metallic object. You will get a slight shock, and sometimes you will hear a small crackling noise. If you have an AM radio nearby, you might hear the crackling sound amplified through the loudspeaker. If you do this experiment in a dark room, you will see a spark leap from the tip of your finger to the metal, like a tiny bolt of lightning. This type of electricity is called static electricity; static is derived from a Greek word meaning "standing."
The electricity is at rest and moves only from you to the metal you touched in one fast movement. Touch the metal again and nothing happens. You "discharged" yourself the first time. Walk across the rug and the discharge will take place once again.
Why? All matter is made up of atoms. The book you are holding, the chair you are sitting in and you, yourself, all are made up of atoms. The atom is the smallest particle into which an element can be divided and still have the chemical properties of that element. Some elements you may be familiar with are oxygen, hydrogen, iron, gold, carbon, and many others. So far, scientists have found 96 elements on our planet.
Atom is a Greek word meaning "indivisible." When atoms were first discovered, scientists believed nothing was smaller. Since we can't see an atom, it is easy to understand why they thought so.
An atom has a tiny, dense core having a positive electrical charge. Its weight accounts for almost 95 percent of the total weight of the atom. This core, or nucleus, is surrounded by one or more negatively charged particles called electrons (see Figure 1). The negative electrons and the positive nucleus balance each other. They remain that way until we scrape our feet across the rug or rub a piece of amber or plastic. At that moment, the material being rubbed picks up negative charges from the material used in the rubbing.
When the atoms are out of balance there is a sudden, very tiny discharge that balances the atoms once again, as the rubbed object gives up electrons to the rubbing material. That is why you felt the small shock when you touched the doorknob.
Experiment No. 2 is going to prove something very important about static electricity. First, you will show that when two objects have like or similar charges they will repel each other. In other words, if they are both negative or are both positive, they will push away from one another. On the other hand, if the one is positive and the other negative, they will attract each other. This attraction will continue only until they have exchanged electrons and have the same charge. Then they will shove each other away. EXPERIMENT NO. 2: GETTING A CHARGE OUT OF POLYETHYLENE AND WOOLCHAPTER 2
Which Way Is North?
We are now going to jump 300 years and thousands of miles to China in the fourth century B.C. It seems there was a powerful Chinese general waging war against the barbarians of the north around 376 B.C. His name was Huang-ti, meaning the "Yellow Emperor." Huang-ti was supposed to be the first to use lodestone as a compass.
There are two ways his compass could have been mounted inside his chariot. One version of the story says that a piece of highly polished lodestone rested on a piece of wood that was so polished that it was slick to the touch. The lodestone-compass turned easily on the polished mounting so it was pointing north. The other version is that the lodestone rested in a wooden bowl that floated in a tank filled with water. As the lodestone turned, it would force the bowl to turn also.
Why did the lodestone point north? This type of iron—magnetite—has permanent poles. One end always points north and the other south. Look at the drawing in Figure 3A. All of the particles are lined up in the same direction. What happens then is that the north pole of the lodestone points south. Like poles repel each other. The south pole of the lodestone points north.
If lodestone is hit hard enough, it will shift some of the particles. Some would point north, some south, and others in every other direction. The lodestone loses its magnetism (see Fig. 3B).
This first compass was used by military commanders during the Han dynasty, a ruling group that controlled China from 206 B.C. to A.D. 220. Strangely, lodestone was not used for ship navigation until 900 years later. It was employed only on land by the generals and by magicians, who used it to find the right place to erect a temple or the right burial places.
Not until the thirteenth century A.D. (about the same time that Italian trader Marco Polo was exploring the Far East) was the compass employed by Chinese navigators for the first time. By this time, they had discovered that a needle could be magnetized and used in a compass by rubbing it with lodestone.
Arab sailors saw the advantages of the compass, adopted it, and brought it to Europe. This resulted in the great period of European exploration. For the first time, shipmasters could easily find their way across the sea without needing to hug the shore. Christopher Columbus undoubtedly used the compass when he left Spain trying to find an easier route to the Indies.
It is very easy to make a compass like the one Columbus may have used. What we're going to do is magnetize an ordinary needle, not with lodestone but with a magnet. In the compass, the needle is delicately balanced so that it is free to move. The needle will point north unless there is a large amount of iron or steel nearby. (See Experiment No. 3 for directions on making a compass).
Experiment No. 4 will illustrate the fields of force that surround each pole of a magnet. We will see why this is important later in the story of electricity.CHAPTER 3
Mr. Gilbert Makes His Mark
Inventions and Discoveries
The next stop in our time travel is sixteenth-century England. While scientists had continued to study magnetic effects, no specific progress was made until William Gilbert (1544-1603) came along. He lived during the time of Shakespeare and was one of Queen Elizabeth's physicians. Like many doctors of his time, he was deeply interested in magnetism. It was thought that since magnetism had certain effects on objects, it might have healing powers for the human body.
He discovered that many substances besides amber could attract light objects, for example (listed alphabetically): amethyst, diamond, glass, jet, opal, rock crystal, sapphire, sulfur, and hard sealing wax. He found that many semiprecious stones could be added to his list. Not all of these substances attracted equally, and he carefully separated them in the order of their ability to attract.
To help gauge the ability of objects to attract, Gilbert invented the versorium (see Fig. 6). This is probably the first electrical instrument to be invented. Versorium is a Latin word meaning "turn about." That is exactly what it did: it turned around. It looked like a mariner's compass, but while the compass employed a magnetized needle, the versorium did not.
Gilbert's invention used a pointer made of almost any solid material, even light wood. Before Gilbert came up with his invention, the way to find whether a rubbed material would attract a light object was to place the two close together and see whether any motion took place. The versorium went one better. A thin pointer balanced at its midpoint would react to the presence of attraction even if there was not enough force to lift the lightest body.
Gilbert describes his invention so well in his book De Magnete (On the Magnet), 1600, that it is easily duplicated. (In those days important matter was always written in Latin. Educated people read and wrote in Latin as easily as we do in English.)
Gilbert described his versorium in such detail that anyone could copy it. But it seems no one did. Almost 100 years were to pass before other electrics were discovered. Other writers just copied Gilbert's list without performing his experiment.
The electroscope, a modern form of Gilbert's versorium, is now used to study atomic particles.
Apart from this invention, Gilbert deserves credit for making up the word electricity. He used the word to describe objects placed near his versorium. Those that were not attracted he called nonelectrics. Those that were attracted, such as paper, straw, and sealing wax, were called electrics because they were attracted to the pointer and made it move.
He discovered other important things during his studies. He found that it was not the heat given off by the rubbing that made amber attract other light objects, but the friction. He also dispelled the theory that air was displaced by the amber or that the attractive quality was owned only by the amber. He proved that substances very different from amber were also electrics.
A Scientific Approach
Gilbert was different from other scientists of his time in his attitude toward his work. After he developed a theory, he would perform various experiments himself in order to find out whether the theory was right or wrong. Most other scientists (or "philosophers," as they called themselves) would work out a theory, but felt it was beneath them to become "workmen" and build the necessary equipment to prove their point.
Gilbert also developed the idea that extensive experimenting should come before coming up with a basis for a theory. You might think you know the reason for the behavior of a substance or the explanation for the action of some natural force. But in order to prove that your theory is true, you have to make up an experiment and repeat it many times, changing it slightly each time.
As an example: Let's say you believe that it is the movement of the trees that makes the wind. You say, "Look, the trees move and there's a wind. I can feel it. Doesn't it prove I'm right?"
To prove or disprove your theory, you must do an experiment. You go to places where there are no trees. There you can feel the wind on your face. Since there is a wind and no trees, it must prove that the wind exists without trees. Of course, to be really scientific, you would have to go to several different places, such as plains, deserts, and mountaintops. You repeat the experiment to check on the accuracy of your observations.
And that's what William Gilbert did. He brought a truly scientific approach to the study of what in those days was still called magnetism, but which today we know to be static electricity. In his honor, a unit of magnetic intensity is called a gilbert.
Excerpted from The Story of Electricity by George deLucenay Leon. Copyright © 1983 George deLucenay Leon. Excerpted by permission of Dover Publications, Inc..
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