The Story of Great Inventions Part 6

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.

And yet inventors have not learned the meaning of this law. They continue trying to invent perpetual-motion machines--machines that will produce work from nothing. This is what a perpetual-motion machine would be if such a machine were possible. For a machine without friction is impossible, and friction means wasted work--work changed into heat. A machine to keep itself running and supply the work wasted in friction must produce work from nothing. The great law of nature is that you cannot get something for nothing. Whether you get work, heat, electricity, or light, something must be used up to produce it. For whatever you get out of a machine you must give an equivalent. This law cannot be evaded, and from it there is no appeal.

Chapter V

GREAT INVENTIONS OF THE NINETEENTH CENTURY

The discoveries of Faraday prepared the way for the great inventions of the nineteenth century. By the middle of the century men knew how to control the wonderful power of electricity. They did not know what electricity is, nor do we know to-day, though we have made some progress in that direction; but to control it and make it furnish light, heat, and power was more important.

Before the inventions of James Watt made it possible to use steam-power, factories were built near falling water, so that water-power could be used. But the steam-engine made it possible to build great factories wherever a supply of water for the boilers could be obtained. Cities were built around the factories. Cities already great became greater.

With the growth of cities the need of a new means of producing light and power made itself felt. Electricity promised to become the Hercules that should perform the tasks of the modern world.

Discovery gave way to invention. During the second half of the nineteenth century many great inventions were made and industries were developed, while discoveries were few until near the close of the century. Within this period the great industries which characterize our modern civilization, and which arose out of the discoveries that science had made in the centuries preceding, attained a high degree of development. In this chapter we shall trace the applications of some of the discoveries with which we have now become familiar. This will lead us into the field of electrical invention, for we are dealing now with the beginning of the world's electrical age.

Electric Batteries

From the time of Volta to the time of Faraday the only means of producing an electric current was the "voltaic battery," so called in honor of Volta. The voltaic cell is the simplest form of electric battery. In this cell the zinc and copper plates are placed in sulphuric acid diluted with water. As the acid eats the zinc, hydrogen gas is formed. This gas collects in bubbles on the copper plate and weakens the current. The aim of inventors was to produce a steady current, to devise a battery in which no gas would collect on the copper plate. They saw the need of a battery that would give out a current of unchanging strength until the zinc or the acid was used up.

The first real improvement in the battery was made by Professor Daniell, of King's College, London. In the Daniell cell the zinc plate is in dilute sulphuric acid, and the copper plate is in a solution of blue vitriol or copper sulphate. Professor Daniell separated the two liquids by placing one of them in a tube formed of the gullet of an ox. This tube dipped into the other liquid. The hydrogen gas, as it was formed by the acid acting on the zinc, could go through the walls of the tube, but was stopped by the copper sulphate, and copper was deposited on the copper plate. This copper deposit in no way interfered with the current, so that the current was not weakened until the zinc plate or one of the solutions was nearly consumed. A cup of porous earthenware is now used in Daniell cells to separate the liquids (Fig. 37). By placing crystals of blue vitriol in the battery jar, the solution of blue vitriol can be kept up to its full strength for a very long time. The zinc in time is consumed, and must be replaced.

[Ill.u.s.tration: FIG. 37--A DANIELL CELL]

In the gravity cell (Fig. 38) the same materials are used as in the Daniell cell--copper in copper sulphate, and zinc in sulphuric acid; but there is no porous cup. The solutions are kept separate by gravity, the heavy copper sulphate being at the bottom. The gravity cell has until recently been extensively used in telegraphy, and continues in use in short-distance telegraphy and in automatic block signals. The gravity and Daniell cells are used for closed-circuit work--that is, for work in which the current is flowing almost constantly.

[Ill.u.s.tration: FIG. 38--A GRAVITY CELL]

The Dry Battery

Another important improvement was the invention of the dry battery. You will remember that the first battery, the one invented by Volta, was a form of dry battery; but it was a very feeble battery compared with the dry batteries now in use, so that we may call the dry battery a new invention. The dry battery is falsely named. There can be no battery without a liquid. In the dry battery the zinc cup forming the outside of the cell is one of the plates of the cell (Fig. 39). The battery appears to be dry because the solution of sal ammoniac is absorbed by blotting-paper or other porous substance in contact with the zinc. The inner plate is carbon, and this is surrounded by powdered carbon and manganese dioxide--the latter to remove the hydrogen gas which collects on the carbon plate. This gas weakens the current when the circuit has been closed for a short time, but is slowly removed when the circuit is broken. Thus the battery is said to "recover."

[Ill.u.s.tration: FIG. 39--SHOWING WHAT IS IN A DRY BATTERY]

The dry cell will give a strong current, but for a short time only. It recovers, however, if allowed to rest. It can be used, therefore, only in "open-circuit" work--such as door-bell circuits, and some forms of fire and burglar alarm. A door-bell circuit is open nearly all the time, the current flowing only while the b.u.t.ton is being pressed. Some forms of wet battery work in the same way as the dry battery, and are used like-wise for open-circuit work. In these batteries carbon and zinc plates in a solution of sal ammoniac are used, the same materials as in the dry battery. The only difference is that in the dry battery the solution is absorbed by some porous substance and the battery sealed so that it appears to be dry.

The Storage Battery

One of the greatest improvements in electric batteries is the storage battery. A simple storage battery may be made by placing two strips of lead in sulphuric acid diluted with water and connecting the lead strips to a battery of Daniell cells or dry cells. In a short time one of the lead strips will be found covered with a red coating. The surface of this lead strip is no longer lead but an oxide of lead, somewhat like the rust that forms on iron. If the lead strips are now disconnected from the other battery and connected to an electric bell, the bell will ring. We have here two plates, one of lead and one of oxide of lead, in dilute sulphuric acid. This forms a storage battery.

The first storage battery was made of two sheets of lead rolled together and kept apart by a strip of flannel. The lead strips thus separated were immersed in dilute sulphuric acid. A current from another battery was pa.s.sed through this cell for a long time--first in one direction, then in the other. This roughened the surface of the lead plates, so that the battery would hold a greater charge. The battery was then charged by pa.s.sing a current through it in one direction only for a considerable length of time. Feeble cells were used for charging. It took days, and sometimes weeks, to charge the first storage batteries.

Then the storage battery would give out a strong current lasting for a few hours. It slowly acc.u.mulated energy while being charged, and then gave out this energy rapidly in the form of a strong electric current.

For this reason the storage battery was called an "acc.u.mulator."

While charging the storage cell there was formed on the negative plate a coating of soft lead, and on the positive plate a coating of dark-brown oxide of lead. It was found better to apply these coatings to the lead plates before making up the battery. Later it was found that the battery would hold a still greater charge if the plates were made in the form of "grids" (Fig. 40), and the cavities filled with the active material--the negative with spongy lead, and the positive with dark-brown lead oxide.

Some excellent commercial storage batteries are made from lead plates by the action of an electric current, very much as Plante made his batteries. Fig. 41 shows one of these plates.

[Ill.u.s.tration: FIG. 40--A STORAGE BATTERY, SHOWING THE "GRIDS"]