Part 6 (1/2)
All this work occupied but ten days in the autumn of 1831, though years of preparation had gone before. In these ten days the foundation was laid for the induction-coil, modern dynamo-electric machinery, and electric lighting. Fig. 33 shows the laboratory in which Faraday did this work.
[Ill.u.s.tration: FIG. 33--FARADAY'S LABORATORY, WHERE THE FIRST DYNAMO WAS MADE From the water-color drawing by Miss Harriet Moore.]
Faraday continued to explore the field opened up before him. In one experiment two small pencils of charcoal lightly touching were connected to the ends of a secondary coil. A spark pa.s.sed between the charcoal points when the primary circuit was closed. This was the first transformer producing a tiny electric light (Fig. 34).
[Ill.u.s.tration: FIG. 34--THE FIRST TRANSFORMER]
Faraday discovered the induction-coil, the dynamo, and the transformer, and he showed that, in each of these, it is magnetism which produces the electric current. He had discovered the secret when he obtained a current by thrusting a magnet into a coil of wire. The s.p.a.ce about a magnet in which the magnet will attract iron he called the ”magnetic field” (Figs. 35 and 36). In every case of magnetism causing an electric current to flow in a coil of wire, the coil is in a magnetic field, and the magnetic field is changing--that is, the magnetic field is made alternately stronger and weaker, or the coil moves across the magnetic field. The point is that magnetism at rest will not produce an electric current. There must be a changing magnetic field or motion. In Faraday's dynamo a copper disk whirled between the poles of a magnet and the whirling of the disk in the magnetic field caused an electric current.
In the modern dynamo it is the whirling of a coil of wire in a magnetic field that causes a current to flow. In the induction-coil it is the change in the magnetic field that causes a current to flow in the secondary coil. A coil of wire with an electric current flowing through it will attract iron like a magnet. The primary coil with a current from a battery flowing through it acts in all respects like a magnet; but as soon as the current ceases to flow the magnetic field disappears--the coil is no longer a magnet. When we make and break the connection between the primary coil and the battery, then, we repeatedly make and destroy the magnetic field, and this changing magnetic field causes a current to flow in the secondary coil. The induction-coil is one form of transformer. We shall see later how the dynamo and the transformer developed in the nineteenth century.
[Ill.u.s.tration: FIG. 35--THE ”MAGNETIC FIELD” IS THE s.p.a.cE AROUND A MAGNET IN WHICH IT WILL ATTRACT IRON The iron filings over the magnet arrange themselves along the ”lines of force.”]
[Ill.u.s.tration: FIG. 36--MAGNETIC FIELD OF A HORSESHOE MAGNET]
When a boy, Faraday had pa.s.sed the current from his little battery through a jar of cistern-water, and saw in the water a ”dense white cloud” descending from the positive wire, and bubbles arising from the negative wire. Something was being taken out of the water by the electric current. When he tried the experiment later in his laboratory, he found that, whenever an electric current is pa.s.sed through water, bubbles of two gases, oxygen and hydrogen, rise through the water. He found that if the current is made stronger the bubbles are formed faster. The water in time disappears, for it has been changed or ”decomposed” into the two gases.
It was the current from a battery that would decompose water. The electricity from the electrical machine would do other things that he had never seen a battery current do. ”Do the battery and the electrical machine produce different kinds of electricity, or is electricity one and the same in whatever way it is produced?” This was the query that troubled him. The answer to this question had been so uncertain that the effect of the voltaic battery had been termed ”galvanism,” while that of the friction machine retained the name ”electricity.”
Faraday tried many experiments in searching for an answer to this question. He found that the electricity of the machine will produce the same effect as that of a battery if the machine is compelled to discharge slowly. An electrical machine or a battery of Leyden jars can be made to give out an electric current, and this current will affect a magnetic needle in the same way that a battery current will. It will magnetize steel. If pa.s.sed through water, it will decompose the water into the two gases oxygen and hydrogen. In short, a current from an electrical machine or a Leyden jar will do everything that a current from an electric battery will do. Faraday caused the Leyden jar to give a current instead of a spark by connecting the two metal coatings with a wet string. On the other hand, the discharge from a powerful electric battery will produce a spark and affect the human nerves in the same way as the discharge from the electrical machine. The same effects may be obtained from one as from the other.
In the discharge from the machine, a small quant.i.ty of electricity is discharged under high pressure, as water may be forced through a small opening by very high pressure. The voltaic cell, on the other hand, furnishes a large quant.i.ty of electricity at low pressure, as a street may be flooded by a broken water-main though the pressure is low. In fact, the quant.i.ty of electricity required to decompose a grain of water is equal to that discharged in a stroke of lightning, while the action of a dilute acid on the one-hundredth part of an ounce of zinc in a battery yields electricity sufficient for a powerful thunder-storm.
Many tests were made, and the result was a convincing proof that electricity is the same whatever its source, the different effects being due to difference in pressure and quant.i.ty. ”But in no case,” said Faraday, ”not even in those of the electric eel and torpedo, is there a production of electric power without something being used up to supply it.”
Faraday's professional work would have made him wealthy. In one year he made 1000 ($5000), and the amount would have increased had he sold his services at their market value. But then there would have been no Faraday the discoverer. The world would have had to wait, no one knows how long, for the laying of the foundations of electrical industries. He chose to give up wealth for the sake of discovery. He gave up professional work with the exception of scientific adviser to Trinity House, the body which has charge of Great Britain's lighthouse service.
Nor did he carry his discoveries to the point of practical application.
As soon as he discovered one principle, he set out in pursuit of others, leaving the practical application to the future.
Faraday loved the beauty of nature. The sunset he called the scenery of heaven. He saw the beauty of electricity, which he said lies not in its mystery, but in the fact that it is under law and within the control of the human intellect.
A Wonderful Law of Nature
Not long after Faraday made his first dynamo, Robert Mayer, a physician from Germany, was making a voyage to the East Indies which proved to be a voyage of discovery. He had sailed as the s.h.i.+p's physician, and after some months an epidemic broke out among the s.h.i.+p's company. In his treatment he drew blood from the veins of the arms. He was startled to see bright-red blood issue from the veins. He might almost have believed that he had opened an artery by mistake. It was soon explained to him by a physician who had lived long in the tropics that the blood in the veins of the natives, and of foreigners as well, in the tropics is of nearly the same color as arterial blood. In colder climates the venous blood is much darker than the arterial.
He reasoned upon this curious fact for some time, and came to the conclusion that the human body does not make heat out of nothing, but consumes fuel. The fuel is consumed in the blood, and there the heat is produced. In the tropics less heat is needed, less fuel is consumed, and therefore there is less change in the color of the blood.
When a man works he uses up fuel. If a blacksmith heats a piece of iron by hammering, the heat given to the iron and the heat produced in his body are together equal to the heat of the fuel consumed in his blood.
The work a man does, as well as the heat of his body, comes from the burning of the fuel in his blood.
What is true of a man is true of an engine. The work the engine does, as well as the heat it produces, comes from the heat of the fuel in the furnace. Mayer found that one hundred pounds of coal in a good working engine produces the same amount of heat as ninety-five pounds in an engine that is not working. In the working engine the heat of the five pounds of coal is used up in the work of running the engine, and therefore does not heat the engine. Heat that is used in running the engine is no longer heat, but work. So Mayer said the heat is not destroyed, but only changed into work. He said, further, that the work of running the engine may be changed again into heat.
Mayer's theory was opposed by many scientific men of Europe. One great scientist said to him that if his theory were correct water could be warmed by shaking. He remembered what the helmsman had remarked to him on the voyage to Java, that water beaten about by a storm is warmer than quiet sea-water; but he said nothing. He went to his laboratory, tried the experiment, and some weeks later returned, exclaiming: ”It is so! It is so!” He had warmed water simply by shaking it.
These results mean that work or energy cannot be destroyed. Though it changes form in many ways, it is never destroyed. Neither can man create energy; he can only direct its changes as the engineer, by the motion of his finger in opening a valve, sets the locomotive in motion. He does not move the locomotive. He directs the energy already in the steam.
Since the time of Galileo, men had caught now and then a glimpse of this great law. Galileo had stated his law of machines; that, when a machine does work, a man or a horse or some other power does an equal amount of work upon the machine. Count Rumford had performed his experiment with the cannon, showing that heat is produced by the work of a horse. Davy had proved that, in the voltaic battery, something must be used up to produce the current--the mere contact of the metals is not sufficient.
Faraday had said that in no case is there a production of electrical power without something being used up to supply it. Mayer stated clearly this law of energy when he said that energy cannot be created or destroyed, but only changed from one form to another.