The Story of Great Inventions

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.

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.

FIG. 38–A GRAVITY CELL 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."

FIG. 39–SHOWING WHAT IS IN A DRY BATTERY 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 button 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 passed 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 passing 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 accumulated 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 "accumulator."

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 PlantÉ made his batteries. Fig. 41 shows one of these plates.

FIG. 40–A STORAGE BATTERY, SHOWING THE "GRIDS" FIG. 40–A STORAGE BATTERY, SHOWING THE "GRIDS"

FIG. 41–A STORAGE-BATTERY PLATE MADE FROM A SHEET OF LEAD FIG. 41–A STORAGE-BATTERY PLATE MADE FROM A SHEET OF LEAD

The storage battery does not store up electricity. It produces a current in exactly the same way as any other battery—by the action of the acid on the plates. When this action ceases it is no longer a battery, though it may be made one again by passing a current through it in the opposite direction from that which it gives out. In this it differs from the voltaic battery, for when such a battery is run down it can be restored only by adding new solution or new plates. The storage battery is especially useful for "sparking" in gas or gasolene motors.

Edison has invented a storage battery that will do as much work as a lead battery of twice its weight. Edison's battery is intended especially for use in electric automobiles. By reducing the weight of the battery which the machine must carry the weight of the truck may also be reduced. In the Edison battery the positive plates are made of a grid of nickel-plated steel containing tubes filled with pure nickel. The negative plate consists of a nickel-plated steel grid containing an oxide of iron similar to common iron-rust.

After working a number of years on this battery and making nine thousand experiments, Edison thought he had it perfected, and indeed it was a great improvement over the storage batteries that had been used—much lighter and cheaper, and more successful in operation. Two hundred and fifty automobiles were equipped with it, and it proved superior to lead batteries for this purpose. But it was not to Edison's liking. He threw the machinery, worth thousands of dollars, on the scrap-heap, and worked on for six years. He had then produced a battery as much better than the first as the first was better than the lead battery, and he was content to have the new battery placed on the market.

The Dynamo

For the purpose of lighting and power the electric battery proved too costly. Davy produced an arc light with a battery of four thousand cells. The arc was about four inches in length and yielded a brilliant light, but as the cost was six dollars a minute it was not thought practical. Attempts were made early in the century to use a battery current for power, but they failed because of the cost and the fact that no good working motor had been invented.

Light and power were needed. Electricity could supply both. But how overcome the difficulty of cost, and produce an electric current from burning coal or falling water? For answer man looked to the great discovery of Faraday and his "new electrical machine." Inventors in Germany, France, England, Italy, and America made improvements until from the disk dynamo of Faraday there had evolved the modern dynamo.

Electroplating and the telegraph are the only applications of the electric current that became factors in the world's industry before the dynamo, yet in long-distance telegraphy and in electroplating to-day the dynamo is used. Without the dynamo, electric lighting, electric power, and electric traction as developed in the nineteenth century would have been impossible; in fact, the dynamo with the electric motor (which, as we shall see, is only a dynamo reversed) is master of the field.

The way had been prepared for the application of Faraday's discovery by William Sturgeon, an Englishman, and Joseph Henry, an American. Sturgeon discovered that soft iron is more quickly magnetized than steel, and found that the strength of an electromagnet can be greatly increased by making the core of a soft-iron rod and bending the rod into the form of a horseshoe (Fig. 42). The iron rod was coated with sealing-wax and wound with a single layer of copper wire, the turns of wire not touching. This was in 1825, before Faraday discovered the principle of the dynamo.

FIG. 42–STURGEON'S ELECTROMAGNET FIG. 42–STURGEON'S ELECTROMAGNET

Professor Henry still further increased the strength of the electromagnet by covering the wire with silk, which made it possible to wind several layers of wire on the iron core, and many times the length of wire that had been used by Sturgeon. Fig. 43 shows such a magnet. One of Henry's magnets weighed fifty-nine and a half pounds, and would hold up a ton of iron. Sturgeon said: "Professor Henry has produced a magnetic force which completely eclipses every other in the whole annals of magnetism." With Professor Henry's invention the electromagnet was ready for use in the dynamo. Fig. 44 shows a strong electromagnet.

FIG. 43–AN ELECTROMAGNET WITH MANY TURNS OF INSULATED WIRE FIG. 43–AN ELECTROMAGNET WITH MANY TURNS OF INSULATED WIRE

FIG. 44–AN ELECTROMAGNET LIFTING TWELVE TONS OF IRON FIG. 44–AN ELECTROMAGNET LIFTING TWELVE TONS OF IRON

A moving magnet causes a current to flow in a coil, but a magnet at rest has no effect. A moving magnet is equal to a battery. In Faraday's experiments a current was induced in a coil of wire by moving a magnet in the coil or by making and breaking the circuit in another coil wound on the same iron core. A current was induced in a metal disk by revolving it between the poles of a magnet. In every case there was motion in a magnetic field, or the field itself was changed. A changing magnetic field is equal to a moving magnet. What is needed to induce a current in a coil, whether it be in a dynamo, an induction-coil, or a transformer, is a changing magnetic field about the coil or motion of the coil in the magnetic field.

If fine iron filings are sprinkled over the poles of a magnet the filings arrange themselves in definite lines. This is a simple experiment which any boy can try for himself. Faraday called the lines marked out by the iron filings "lines of force" (the lines of force of a horseshoe magnet are shown in Fig. 36), because they indicate the direction in which the magnet pulls a piece of iron—that is, the direction of the magnetic force. Now, if a current is to be induced in a wire, the wire must move across the lines of force. If the wire moves along the lines marked out by the iron filings, there will be no current. When a coil rotates between the poles of a magnet, the wire moves across the lines of force and a current is induced in the coil if the circuit is closed. This is the way a current is produced in a dynamo.

Faraday produced a current by rotating a coil between the poles of a steel magnet. He made a number of such machines, and used them with some success in producing lights for lighthouses, but the defects of these machines were so great that the lighting of a city or the development of power on a large scale was impractical. The electromagnet was needed to solve the problem.

Siemens' Dynamo

The war of 1866 between Austria and Prussia and the certainty of a coming struggle with France turned the attention of German inventors to the use of electricity in warfare. Werner von Siemens, an artillery officer, was improving an exploding device for mines. An electric current was needed to produce a spark or heat a wire to redness in the powder. Faraday had used a coil of wire turning between the poles of a steel magnet to produce a current. In England a coil turning between the poles of an electromagnet had been used, but the electromagnet received its current from another machine in which a steel magnet was used. Siemens found that the steel magnet could be dispensed with, and that a coil turning between the poles of an electromagnet could furnish the current for the electromagnet. Two things are needed, then, to make a dynamo: an electromagnet and a coil to turn between the poles of that magnet. The rotating coil, which usually contains a soft-iron core, is called the "armature." The coil will furnish current for the magnet and some to spare; in fact, only a small part of the current induced in the coil is needed to keep the magnet up to its full strength, and the greater part of the current may be used for lighting or power. The new machine was named by its inventor "the dynamo-electric machine." The name has since been shortened to "dynamo." The first practical problem which the dynamo solved was the construction of an electric exploding apparatus without the use of steel magnets or batteries. A dynamo with Siemens' armature is shown in Fig. 45.

FIG. 45–A DYNAMO WITH SIEMENS' ARMATURE FIG. 45–A DYNAMO WITH SIEMENS' ARMATURE

In his first enthusiasm the inventor dreamed of great things for the new machine, among others an electric street railway in Berlin. But the dynamo was not yet ready. The difficulty was the heating of the iron core of the armature, caused by the action of induced currents. There are induced currents in the iron core as well as in the coil, and, for the same reason, the coil and the iron core within it are both moving in a magnetic field. These little currents circling round and round in the iron core produce heat. The rapid changing of the magnetism of the iron also heats the iron.

It remained for Gramme, in France, to apply the proper remedy. This remedy was an armature in which the coil was wound on an iron ring, invented by an Italian, Pacinotti. Gramme applied the principle discovered by Siemens to Pacinotti's ring, and produced the first practical dynamo for strong currents. This was in 1868. A ring armature is shown in Fig. 46. The first dynamo patented in the United States is shown in Fig. 47. This dynamo is only a curiosity.

FIG. 46–RING ARMATURE FIG. 46–RING ARMATURE

FIG. 47–FIRST DYNAMO PATENTED IN THE UNITED STATES FIG. 47–FIRST DYNAMO PATENTED IN THE UNITED STATES

Intended to be used for killing whales.

Photo by Claudy.

The Drum Armature

An improvement in the Siemens armature was made four years later by Von Hefner-Alteneck, an engineer in the employ of Siemens. This improvement consisted in winding on the iron core a number of coils similar to the one coil of the Siemens armature, but wound in different directions. This is called the "drum armature" (Fig. 48). The heating of the core is prevented by building it up of a number of thin iron plates insulated from one another and by air-spaces within the core. The insulation prevents the small currents from flowing around in the core. The air-spaces serve for cooling. The drum armature was a great improvement over both the Siemens and the Gramme armatures. With the Siemens one-coil armature there is a point in each revolution at which there is no current. The current, therefore, varies during each revolution of the armature from zero to full strength. In the Gramme armature only half the wire, the part on the outside of the ring, receives the full effect of the magnetic field. The inner half is practically useless, except to carry the current which is generated in the outer half. Both these difficulties are avoided in the drum armature. The dynamos of to-day are modifications of the two kinds invented by Siemens and Gramme. Many special forms have been designed for special kinds of work.

FIG. 48–A DRUM ARMATURE, SHOWING HOW AN ARMATURE OF FOUR COILS IS WOUND FIG. 48–A DRUM ARMATURE, SHOWING HOW AN ARMATURE OF FOUR COILS IS WOUND

Edison's Compound-Wound Dynamo

Edison, in his work on the electric light and the electric railway, made some important improvements in the dynamo. The armature of a dynamo is usually turned by a steam-engine. Edison found that much power was wasted in the use of belts to connect the engine and the dynamo. He therefore connected the engine direct to the dynamo, placing the armature of the dynamo on the shaft of the engine. He also used more powerful field-magnets than had been used before. His greatest improvement, however, was in making the dynamo self-regulating, so that the dynamo will send out the strength of current that is needed. Such a dynamo will send out more current when more lights are turned on. Whether it supplies current for one light or a thousand, it sends out just the current that is needed—no more, no less. It will do this if no human being is near. An attendant is needed only to keep the machinery well oiled and see that each part is in working order. Edison brought about this improvement by his improved method of winding. This method is known as "compound winding."

To understand compound winding we must first understand two other methods of winding. In the series winding (Fig. 49), all the current generated in the armature flows through the coils of the field-magnet. There is only one circuit. The same current flows through the coils of the magnet and through the outer circuit, which may contain lights or motors. Such a dynamo is commonly used for arc lights. It will not regulate itself. If left to itself it will give less electrical pressure when more pressure is needed. It requires a special regulator.

FIG. 49–A SERIES-WOUND DYNAMO FIG. 49–A SERIES-WOUND DYNAMO

In the second form of winding the current is divided into two branches. One branch goes through the coils of the field-magnet. The other branch goes through the line wire for use in lights or motors. This is called the "shunt winding" (Fig. 50). The shunt-wound dynamo is used for incandescent lights. It also requires a special regulator, for if left to itself it gives less electrical pressure when the pressure should be kept the same.

FIG. 50–A SHUNT-WOUND DYNAMO FIG. 50–A SHUNT-WOUND DYNAMO

The compound winding (Fig. 51), which was first used by Edison, is a combination of the series and shunt windings.

FIG. 51–A COMPOUND-WOUND DYNAMO FIG. 51–A COMPOUND-WOUND DYNAMO

The current is divided into two branches. One branch goes only through the field-coils. The other branch goes through additional coils which are wound on the field-magnet, and also through the external circuit. Such a dynamo can be made self-regulating, so that it will give always the same electrical pressure whatever the number of lamps or motors thrown into the circuit. In maintaining always the same pressure it of course supplies more or less current, according to the amount of current that is needed. This is clear if we compare the flow of electric current with the flow of water. Open a water-faucet and notice how fast the water flows. Then open several other faucets connected with the same water-pipe. Probably the water will not flow so fast from the first faucet. That is because the pressure has been lowered by the flow of water from the other faucets. If we could make the water adjust its own pressure and keep the pressure always the same, then the water would always flow at the same rate through a faucet, no matter how many other faucets were opened. This is what happens in the Edison compound-wound dynamo. Turn on one 16-candle-power carbon lamp. It takes about half an ampere of current. Turn on a hundred lamps connected to the same wires, and the dynamo of its own accord keeps the pressure the same, and supplies fifty amperes, or half an ampere for each lamp. With this invention of Edison the dynamo was practically complete, and ready to furnish current for any purpose for which current might be needed. Fig. 52 shows one of Edison's first dynamos. Fig. 53 shows a dynamo used for lighting a railway coach.

FIG. 52–ONE OF EDISON'S FIRST DYNAMOS FIG. 52–ONE OF EDISON'S FIRST DYNAMOS

Permission of Association of Edison Illuminating Companies.

FIG. 53–A DYNAMO MOUNTED ON THE TRUCK OF A RAILWAY CAR FIG. 53–A DYNAMO MOUNTED ON THE TRUCK OF A RAILWAY CAR

The dynamo furnishes current for the electric lights in the car. When the train is not running the current is furnished by a storage battery.

Electric Power

It has been said that the nineteenth century was the age of steam, but the twentieth will be the age of electricity. Before the end of the nineteenth century, however, electric power had become a reality, and there remained only development along practical lines.

We must turn to Oersted, AmpÈre, and Faraday to find the beginning of electric power. In Oersted's experiment, motion of a magnet was produced by an electric current. AmpÈre found that electric currents attract or repel each other, and this because of their magnetic action. Faraday found that one pole of a magnet will spin round a wire through which a current is flowing. Here was motion produced by an electric current. These great scientists discovered the principles that were applied later by inventors in the electric motor.

A number of motors were invented in the early years of the century, but they were of no practical use. It was not until after the invention of the Gramme and Siemens dynamos that a practical motor was possible. It was found that one of these dynamos would run as a motor if a current were sent through the coils of the armature and the field-magnet; in fact, the current from one dynamo may be made to run another similar machine as a motor. Thus the dynamo is said to be reversible. If the armature is turned by a steam-engine or some other power, a current is produced. If a current is sent through the coils, the armature turns and does work. If the machine is used to supply an electric current, it is a dynamo. If used to do work—as, for example, to propel a street-car and for that purpose receives a current—it is a motor. The same machine may be used for either purpose. In practice there are some differences in the winding of the coils of dynamos and motors, yet any dynamo can be used as a motor and any motor can be used as a dynamo. This discovery made it possible to transmit power to a distance with little waste as well as to divide the power easily. The current from one large dynamo may light streets and houses, and at the same time run a number of motors in factories or street-cars at great distances apart. A central-station dynamo may run the motors that propel hundreds of street-cars. Dynamos at Niagara furnish current for motors in Buffalo and other cities. One great scientist, who no doubt fore-saw the wonders of electricity which we know so well to-day, said that the greatest discovery of the nineteenth century was that the Gramme machine is reversible.

The First Electric Railway

The electric railway was made possible by the invention of the dynamo and the discovery that the dynamo is reversible. At the Industrial Exposition in Berlin in 1879 there was exhibited the first practical electric locomotive, the invention of Doctor Siemens. The locomotive and its passenger-coach were absurdly small. The track was circular, and about one thousand feet in length. This diminutive railway was referred to by an American magazine as "Siemens' electrical merry-go-round." But the electrical merry-go-round aroused great interest because of the possibilities it represented (Fig. 54).

FIG. 54–FIRST ELECTRIC LOCOMOTIVE FIG. 54–FIRST ELECTRIC LOCOMOTIVE

The current was generated by a dynamo in Machinery Hall, this dynamo being run by a steam-engine. An exactly similar dynamo mounted on wheels formed the locomotive. The current from the dynamo in Machinery Hall was used to run the other as a motor and so propel the car. The rails served to conduct the current. A third rail in the middle of the track was connected to one pole of the dynamo and the two outer rails to the other pole. A small trolley wheel made contact with the third rail. The rails were not insulated, but it was found that the leakage current was very small, even when the ground was wet.

The success of this experiment aroused great interest, not only in Germany, but in Europe and America. America's greatest inventor, Edison, took up the problem. Edison employed no trolley line or third rail, but only the two rails of the track as conductors, sending the current out through one rail and back through the other. Of course, this meant that the wheels must be insulated, so that the current could flow from one rail to the other only through the coils of the motor.

As in Siemens' experiment, the motor was of the same construction as the dynamo. The rails were not insulated, and it was found that, even when the track was wet, the loss of electric current was not more than 5 per cent. Edison found that he could realize in his motor 70 per cent. of the power applied to the dynamo, whereas the German inventor was able to realize only 60 per cent. The improvement was largely due to the improved winding. Edison was the first to use in practical work the compound-wound dynamo, and this was done in connection with his electric railway. Fig. 55 shows Edison's first electric locomotive.

FIG. 55–FIRST EDISON ELECTRIC LOCOMOTIVE FIG. 55–FIRST EDISON ELECTRIC LOCOMOTIVE

The question of gearing was a troublesome one. The armature shaft of the motor was at first connected by friction gearing to the axle of two wheels of the locomotive. Later a belt and pulleys were used. An idler pulley was used to tighten the belt. When the motor was started and the belt quickly tightened the armature was burned out. This happened a number of times. Then Mr. Edison brought out from the laboratory a number of resistance-boxes, placed them on the locomotive, and connected them in series with the armature. These resistances would permit only a small current to flow through the motor as it was starting, and so prevent the burning-out of the armature coils. The locomotive was started with the resistance-boxes in circuit, and after gaining some speed the operator would plug the various boxes out of circuit, and in that way increase the speed. When the motor is running there is a back-pressure, or a pressure that would cause a current to flow in the opposite direction from that which is running the motor. Because of this back-pressure the current which actually flows through the motor is small, and the resistance-boxes may be safely taken out of the circuit. Finding the resistance-boxes scattered about under the seats and on the platform as they were a nuisance, Mr. Edison threw them aside, and used some coils of wire wound on the motor field-magnet which could be plugged out of the circuit in the same way as the resistance-boxes. This device of Edison's was the origin of the controller, though in the controller now used on street-cars not only is the resistance cut out as the speed of the car increases, but the electrical connections of the motor are changed in such a way as to increase its speed gradually. Fig. 56 shows Edison's first passenger locomotive.

FIG. 56–EDISON'S FIRST PASSENGER LOCOMOTIVE FIG. 56–EDISON'S FIRST PASSENGER LOCOMOTIVE

The news of the little electric railway at the Industrial Exposition in Berlin was soon noised abroad, and the German inventor received inquiries from all parts of the world, indicating that efforts would be made in other countries to develop practical electrical railways. The firm of Siemens & Halske therefore determined to build a line for actual traffic, not for profit, but that Germany might have the honor of building the first practical electric railway. The line was built between Berlin and Lichterfelde, a distance of about one and a half miles. A horse-car seating twenty-six persons was pressed into service. A motor was mounted between the axles, and a central-station dynamo exactly like the motor was installed. As in Edison's experimental railway, the two rails of the track were used to carry the current. This electric line replaced an omnibus line, and was immediately used for regular traffic, and thus the electric railway was launched upon its remarkable career. The first electric car used for commercial service is shown in Fig. 57.

FIG. 57–FIRST COMMERCIAL ELECTRIC RAILWAY FIG. 57–FIRST COMMERCIAL ELECTRIC RAILWAY

An old horse-car converted into an electric car.

Electric Lighting

From the time when the night-watchman carried a lantern to the time of brilliantly lighted streets was less than a century. It was a time when the rapid growth of railways and commerce brought about a rapid growth of cities, and with the growth of cities the need of illumination. Factories must run at night to meet the world's demands. Commerce cannot stop when the sun sets. The centres of commerce must have light.

During this time scientists were at work in their laboratories developing means for producing a high vacuum. They were able to pump the air out of a glass bulb until less than a millionth part of the air remained. They little dreamed that there was any connection between the high vacuum and the problem of lighting. Discoverers were at work bringing to light the principles now utilized in the dynamo. In the fulness of time these factors were brought together to produce an efficient system of lighting.

For a time gas replaced the lantern of the night-watchman, only to yield the greater portion of the field to its rival, electricity.

The first efforts were in the direction of the arc light. From the earliest times the light given out by an electric spark had been observed. It was the aim of inventors to produce a continuous spark that should give out a brilliant light. It was thought for a time that the electric battery would solve the problem, but the cost of the battery current was too great. Again we are indebted to Faraday, for it was the dynamo that made electric lighting possible.

An arc light is produced by an electric current flowing across a gap between two sticks of carbon. The air offers very great resistance to the flow of electric current across this gap. Now whenever an electric current flows through something which resists its flow, heat is produced. The high resistance of the air-gap causes such intense heat that the tips of the carbons become white hot and give out a brilliant light. If examined through a smoked glass a beautiful blue arc of carbon vapor may be seen between the carbon tips. If the current flows in one direction only, one of the carbons, the positive, becomes hotter and brighter than the other.

In 1878 the streets of Paris were lighted with the "Jablochkoff candle," a form of arc light supplied with current by the Gramme machine. In the same year the Brush system of arc lighting was given to the public. This was the beginning of our present system of arc lighting.

The electric arc is suitable for lighting streets and for large buildings, but cannot be used for lighting houses. The light is too intense. One arc would furnish enough light for a number of houses if the light could be divided so that there might be just the right amount of light in each room. But this is impossible with the electric arc. The Edison system of incandescent lighting was required to solve the problem of lighting houses by electricity.

In 1880 the Edison system was brought out for commercial use. Edison's problem was to produce a light that could be divided into a number of small lights, and one that would require less attention than the arc light. He tried passing a current through platinum wire enclosed in a vacuum. This gave a fairly good light, but was not wholly satisfactory. He sat one night thinking about the problem, unconsciously fingering a bit of lampblack mixed with tar which he had used in his telephone. Not thinking what he was doing, he rolled this mixture of tar and lampblack into a thread. Then he noticed what he had done, and the thought occurred to him: "Why not pass an electric current through this thread of carbon?" He tried it. A faint glow was the result. He felt that he was on the right track. A piece of cotton thread must be heated in a furnace in an iron mold, which would prevent the thread from burning by keeping out the air. Then all the other elements that were in the thread would be driven out and only the carbon remain. For three days he worked without sleep to prepare this carbon filament. At the end of two days he succeeded in getting a perfect filament, but when he attempted to seal it in the glass bulb it broke. He patiently worked another day, and was rewarded by securing a good carbon filament, sealed in a glass globe. He pumped the air out of this globe, sealed it, and sent a current through the carbon thread. He tried a weak current at first. There was a faint glow. He increased the current. The thread glowed more brightly. He continued to increase the current until the slender thread of carbon, which would crumble at a touch, was carrying a current that would melt a wire of platinum strong enough to support a weight of several pounds. The carbon gave a bright light. He had found a means of causing the electric current to furnish a large number of small lights. Fig. 58 is an excellent photograph of Edison at work in his laboratory. Fig. 59 shows some of Edison's first incandescent lamps. He next set out in search of the best kind of carbon for the purpose. He carbonized paper and wood of various kinds—in fact, everything he could find that would yield a carbon filament. He tried the fibres of a Japanese fan made of bamboo, and found that this gave a better light than anything he had tried before. He then began the search for the best kind of bamboo. He learned that there are about twelve hundred varieties of bamboo. He must have a sample of every variety. He sent men into every part of the world where bamboo grows. One man travelled thirty thousand miles and had many encounters with wild beasts in his search for the samples of bamboo. At last a Japanese bamboo was found that was better than any other. The search for the carbon fibre had cost about a hundred thousand dollars. Later it was found that a "squirted filament" could be made that worked as well as the bamboo fibre. This was made by dissolving cotton wool in a certain solution, and then squirting this solution through a small hole into a small tank containing alcohol. The alcohol causes the substance to set and harden, and thus forms a carbon thread the size of the hole. Fig. 60 shows the first commercial electric-lighting plant, which was installed on the steamship Columbia in 1880.

FIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORY FIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORY

FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870 FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870

FIG. 60–FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880 FIG. 60–FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880

The carbon thread in the incandescent light is heated to a white heat, and because it is so heated it gives out light. In air such a tiny thread of white-hot carbon would burn in a fraction of a second. The carbon must be in a vacuum, and so the air is pumped out of the light bulb with a special kind of air-pump invented not long before Edison began his work on the electric light. This pump is capable of taking out practically all the air that was in the bulb. Perhaps a millionth part of the original air remains.

A great invention is never completed by one man. It was to be expected that the electric light would be improved. A number of kinds of incandescent light have been devised, using different kinds of filaments and adapted to a variety of uses. The original Edison carbon lamp, however, continues in use, being better adapted to certain purposes than the newer forms.

The mercury vapor light deserves mention as a special form of arc light. In the ordinary arc light the arc is formed of carbon vapor, and the light is given out from the tips of the white-hot carbons. In the mercury vapor light the light is given out from the mercury vapor which forms the arc. This arc may be of any desired length, and yields a soft, bluish-white light which is a near approach to daylight.

The Telegraph

The need of some means of giving signals at a distance was early felt in the art of war. Flag signals such as are now used by the armies and navies of the world were introduced in the middle of the seventeenth century by the Duke of York, admiral of the English fleet, who afterward became James II. of England. Other methods of communicating at a distance were devised from time to time, but the distance was only that at which a signal could be seen or a sound heard. No means of communicating over very long distances was possible until the magnetic action of an electric current was discovered. When Oersted's discovery was made known men began to think of signalling to a distance by means of the action of an electric current on a magnetic needle. A current may be sent over a very long wire, and it will deflect a magnetic needle at the other end. The movements of the needle may be controlled by opening and closing the circuit, and a system of signals or an alphabet may be arranged. A number of needle telegraphs were invented, but they were too slow in action. Two other great inventions were needed to prepare the way for the telegraph. One was the electromagnet in the form developed by Professor Henry, a horseshoe magnet with many turns of silk-covered wire around the soft-iron core, so that a very feeble current will produce a magnet strong enough to move an armature of soft iron. The magnet has this strength because the current flows so many times around the iron core. Another need was that of a battery that could be depended on to give a constant current for a considerable length of time. This need was met by the Daniell cell.

The electromagnet made the telegraph possible. The locomotive made it a necessity. Without the telegraph it would be impossible to control a railway system from a central office. A train after leaving the central station would be like a ship at sea before the invention of the wireless telegraph. Nothing could be known of its movements until it returned. The need of a telegraph was keenly felt in America when the new republic was extended to the Pacific Coast. An English statesman said, after the United States acquired California, that this marked the end of the great American Republic, for a people spread over such a vast area and separated by such natural barriers could not hold together. He did not know that the iron wire of the telegraph would bind the new nation firmly together.

The Morse telegraph system now in use throughout the civilized world was made possible by the work of Sturgeon and Henry. Sturgeon's electromagnet might have been used for telegraphy through very short distances, but Henry's magnet, with its coils of many turns of insulated wire, was needed for long-distance signalling. In one of the rooms of the Albany Academy, Professor Henry caused an electromagnet to sound a bell when the current was transmitted through more than a mile of wire. This might be called the first electromagnetic telegraph. But the application to actual practice was made by Morse, and the man who first makes the practical application of a principle is the true inventor.

In 1832, on board the packet-ship Sully, Samuel F. B. Morse, an American artist, forty-one years of age, was returning from Europe. In conversation a Doctor Jackson referred to the electrical experiments of AmpÈre, which he had witnessed while in Europe, and, in reply to a question, said that electricity passes instantaneously over any known length of wire. The thought of transmitting words by means of the electric current at once took possession of the artist's mind. After many days and sleepless nights he showed to friends on board the drawings and notes he had made of a recording telegraph.

In New York, in a room provided by his brothers, he gave himself up to the working-out of his idea, sleeping little and eating the simplest food. Receiving an appointment as professor in the University of the City of New York, he moved to one of the buildings of that university and continued his experiments in extreme poverty, and at times facing starvation, as his salary depended on the tuition fees of his pupils.

A story told by one of his pupils describes his condition at the time.

"I engaged to become one of Morse's pupils. He had three others. I soon found that the professor had little patronage. I paid my fifty dollars; that settled one quarter's tuition. I remember, when the second was due, my remittance from home did not come as expected, and one day the professor came in and said, courteously:

"'Well, Strother, my boy, how are we off for money?'

"'Why, professor, I am sorry to say I have been disappointed; but I expect a remittance next week.'

"'Next week!' he repeated, sadly; 'I shall be dead by that time.'

"'Dead, sir?'

"'Yes; dead by starvation!'

"I was distressed and astonished. I said, hurriedly: 'Would ten dollars be of any service?'

"'Ten dollars would save my life; that is all it would do.'"

The money was paid, all the student had, and the two dined together. It was Morse's first meal in twenty-four hours.

The Morse telegraph sounder (Fig. 61) consists of an electromagnet and a soft-iron armature. When no current is flowing the armature is held away from the magnet by a spring. When the circuit is closed a current flows through the coils of the magnet and the armature is attracted, causing a click. When the circuit is broken the spring pulls the armature away from the magnet, causing another click. The circuit is made and broken by means of a key at the other end of the line. In Morse's first instrument (Fig. 62) the armature carried a pen, which was drawn across a ribbon of paper when the armature was attracted by the magnet. If the pen was held by the magnet for a very short time, a dot was made; if for a longer time, a dash. The pen was soon discarded, and the message taken by sound only. The Morse alphabet now in use was devised by a Mr. Vail, who assisted Morse in developing the telegraph. The thought occurred to Mr. Vail that he could get help from a printing-office in deciding the combinations of dots and dashes that should be used for the different letters. The letters requiring the largest spaces in the type-cases are the ones that occur most frequently, and for these letters he used the simplest combinations of dots and dashes.

A pen was attached to the pendulum and drawn across the strip of paper by the action of the electromagnet. The lead type shown in the lower right-hand corner was used in making electrical contact when sending a message. The modern instrument shown in the lower left-hand corner is the one that sent a message around the world in 1896.

Photo by Claudy.

Morse repeatedly said that, if he could make his telegraph work through ten miles, he could make it work around the world. This promise of long-distance telegraphy he fulfilled by the use of the relay. The relay works in the same way as the sounder. The current coming over a long line may be too feeble to produce a click that can be easily heard, yet strong enough to magnetize the coils of the relay and cause the armature to close another circuit. This second circuit includes the sounder and a battery in the same station as the sounder, which we shall call "the local battery." The relay simply acts as a contact key, and closes the circuit of the local battery. Thus the current from the local battery flows through the sounder and produces a loud click. Sometimes a relay is used to control a second very long circuit. At the farther end of the second circuit may be a sounder or a second relay which controls a third circuit. Any number of circuits may be thus connected by means of relays. This is a form of repeating system used for telegraphing over very long distances. Fig. 63 shows a circuit with relay and sounder.

FIG. 63–A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDER FIG. 63–A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDER

In the telegraphic circuit only one connecting wire is needed. The earth, being a good conductor of electricity, is used as part of the circuit. It is necessary, therefore, to make a ground connection at each end of the line, the instruments being connected between the line wire and the earth. For long-distance telegraphy a current from a dynamo is used instead of a battery current. Fig. 64 shows a simple telegraphic circuit.

FIG. 64–A SIMPLE TELEGRAPHIC CIRCUIT FIG. 64–A SIMPLE TELEGRAPHIC CIRCUIT

Two keys are shown at K K, and two switches at S S. When one key is to be used the switch at that station must be open, and the switch at the other station closed.

A telegraphic message travels with the speed of light, for the speed of electricity and the speed of light are the same. A telegraphic signal would go more than seven times around the earth in one second if it travelled on one continuous wire. The relays that must be used, however, cause some delay.

In 1835 Morse's experimental telegraph was completed, and in 1837 it was exhibited to the public, but seven years more passed before a line was established for public use. Aid from Congress was necessary. Going to Washington, Morse exhibited his instrument in the halls of the Capitol, sending messages through ten miles of wire wound on a reel. The invention was ridiculed, but the inventor did not despair. A bill for an appropriation to establish a telegraphic line between Washington and Baltimore passed the House by a small majority. The last day of the session came. Ten o'clock at night, two hours before adjournment, and the Senate had not acted. A senator advised Morse to go home and think no more of it, saying that the Senate was not in sympathy with his project. He went to his hotel, counted his money, and found that he could pay his bill, buy his ticket home, and have thirty-seven cents left. All through his work he had firmly believed that a Higher Power was directing his work, and bringing to the world, through his invention, a new and uplifting force; and so when all seemed lost he did not lose heart.

In the morning a friend, Miss Ellsworth, called and offered her congratulations that the bill had been passed by the Senate and thirty thousand dollars appropriated for the telegraph. Being the first to bring the news of his success, Mr. Morse promised her that the first message over the new line should be hers. In about a year the line was completed, and Miss Ellsworth dictated the now famous message: "What hath God wrought!"

Soon afterward the Democratic Convention, in session in Baltimore, received a telegraphic message from Senator Silas Wright, in Washington, declining the nomination for the Vice-Presidency, which had been tendered him. The convention refused to accept a message sent by telegraph, and sent a committee to Washington to investigate. The message was confirmed, and Morse and his telegraph became famous. Fig. 65 shows the first telegraph instrument used for commercial work.

FIG. 65–FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL WORK FIG. 65–FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL WORK

Photo by Claudy.

The desire to telegraph across the ocean came with the introduction of the telegraph on land. Bare wires in the air with glass insulators at the poles are used for land telegraphy, but bare wires in the water could not be used, for ocean water will conduct electricity. Something was needed to cover the wire, protect it from the water, and prevent the escape of the electric current. Just when it was needed such a substance was discovered. In 1843, when Morse was working on his telegraph, it was found that the juice of a certain kind of tree growing in the Malayan Archipelago formed a substance somewhat like rubber but more durable, and especially suited to the insulation of wires in water. This substance is gutta-percha. Ocean cables are made of a number of copper wires, each wire covered with gutta-percha, the wires twisted together and protected with tarred rope yarn and an outer layer of galvanized iron wires. The earth is used for the return circuit, as in the land telegraph.

Duplex Telegraphy

The telegraph was a success, but many improvements were yet to be made. Economy of construction was the thing sought for. To make one wire do the work of two was accomplished by the invention of the duplex system. In duplex telegraphy two messages may be sent in opposite directions over the same wire at the same time. Let us take a look at some of the methods by which this is accomplished.

One method with a long name but very simple in its working is the differential system (Fig. 66). In the differential system the current from the home battery divides into two branches passing around the coils of the electromagnet in opposite directions. Now if these two branches are so arranged that the currents flowing through them are equal, the relay will not be magnetized, because one current would tend to make the end A a north pole, and the other current would tend to make the same end a south pole. The result is that the relay coil is not magnetized, and does not attract the armature. But the current from the distant battery comes over one of these branches only, and will magnetize the relay. Hence, with a similar arrangement at the second station, two messages may be sent at the same time in opposite directions.

FIG. 66–HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME FIG. 66–HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME

Another method not quite so simple in principle is the bridge method. When the key at station A (see Fig. 67) is closed, the current from the battery at station A divides at C, and if the resistances 1 and 2 are equal, and the resistance 3 is equal to the resistance of the line, no current will flow through the sounder. But if a current comes over the line from the distant station this current divides at D, and a part goes through the sounder, causing it to click. The sounder is not affected, therefore, by the current from the home battery, but is affected by the current from the distant battery. Therefore, a message may be sent and another received at the same time. If there is a similar arrangement at the other station, two messages may travel over the line in opposite directions at the same time.

FIG. 67–HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME. BRIDGE METHOD FIG. 67–HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME. BRIDGE METHOD

The differential method is used in land telegraphy, the bridge method almost exclusively in submarine telegraphy. The next step was a quadruplex system, by means of which four messages may be transmitted over one wire at the same time. The first quadruplex system was invented by Edison in 1874, and in four years it saved more than half a million dollars. Other systems have been invented which make it possible to send even a larger number of messages at one time over a single wire.

The Telephone

The idea of "talking by telegraph" began to grow in the minds of inventors soon after the Morse instrument came into use. The sound of the voice causes vibrations in the air. (This is simply shown in the string telephone. This telephone is made by stretching a thin membrane, such as thin sheepskin, or gold-beaters' skin, over a round frame of wood or metal. Two such instruments are connected by a string, the end of the string being fastened to the middle of the stretched membrane. The sound of the voice causes this membrane to vibrate. As the membrane moves rapidly back and forth, it pulls and releases the string, and so causes the membrane at the other end to vibrate and give out the sound. This is the actual carrying of the sound vibrations along the string.) In the telephone it is not sound vibrations but an electric current that travels over the line wire. The telephone message, therefore, travels with the speed of electricity, not with the speed of sound. If it travelled with the speed of sound in air, a message spoken in Chicago would be heard in New York one hour later; but we know that a message spoken in Chicago may be heard in New York the instant it is spoken.

The telephone, like the telegraph, depends on the electromagnet. The thought of inventors at first was to make the vibrations of a thin membrane, caused by the sound of the voice, open and close a telegraphic circuit. An electromagnet at the other end of the line would cause a thin membrane with a piece of soft iron attached to it to vibrate, just as the magnet in the telegraph receiver pulls and releases the soft-iron armature as the circuit is made and broken. The thin membrane caused to vibrate in this way would give out the sound. A telephone on this principle was invented by Philip Reis, a schoolmaster in Germany. The transmitter was carved out of wood in the shape of a human ear, the thin membrane being in the position of the ear-drum. Musical sounds and even words were transmitted by this telephone, but it could never have been successful as a practical working telephone. The membrane in the receiver would vibrate with the same speed as the membrane in the transmitter, but sound depends on something more than speed of vibration.

The Bell telephone, as known to-day, began with a study of the human ear. Alexander Graham Bell was a teacher of the deaf. His aim was to teach the deaf to use spoken language, and for this purpose he wished to learn the nature of the vibrations caused by the voice. His plan was to cause the ear itself to trace on smoked glass the waves produced by the different letters of the alphabet, and to use these tracings in teaching the deaf. Accordingly, a human ear was mounted on a suitable support, the stirrup-bone removed, leaving two bones attached, and a stylus of wheat straw attached to one of the bones. The ear-drum, caused to vibrate by the sound, moved the two small bones and the pointer of straw, so that when he sang or talked to the ear delicate tracings were made on the glass.

This experiment suggested to Mr. Bell that a membrane heavier than the ear-drum would move a heavier weight. If the ear-drum, no thicker than tissue-paper, could move the bones of the ear, a heavier membrane might vibrate a piece of iron in front of an electromagnet. He was at the same time devising a telegraph for transmitting messages by means of musical sounds. In this telegraph he was using an electromagnet in the transmitter and another electromagnet in the receiver. He attached the soft-iron armature of each electromagnet to a stretched membrane of gold-beaters' skin, expecting that the sound of his voice would cause the membrane of the transmitter to vibrate, and that, by means of the electromagnets, the membrane of the receiver would be made to vibrate in the same way (Fig. 68). At first he was disappointed, but after making some changes in the armatures a distinct sound was heard in the receiver. Later the membrane was discarded, and a thin iron disk used with better effect.

FIG. 68–FIRST BELL TELEPHONE RECEIVER AND TRANSMITTER FIG. 68–FIRST BELL TELEPHONE RECEIVER AND TRANSMITTER

The receiver is on the left in the picture. A thin membrane of gold-beaters' skin tightly stretched and fastened with a cord can be seen on the end of the transmitter and of the receiver. An electromagnet is also shown over each membrane. This thin membrane, with a piece of soft iron attached, was used in place of the soft-iron disk of the modern receiver.

The story of Bell's struggles might seem like the repetition of the life story of many another great inventor. He knew that he had discovered something of great value to the world. He devoted his time to the perfecting of the telephone, neglecting his professional work and finally giving it up, that he might give his whole time to his invention. He was forced to endure poverty and ridicule. He was called "a crank who says he can talk through a wire." Men said his invention could never be made practical. Even after he succeeded in finding a few purchasers and some of the telephones were in actual use, people were slow to adopt it. The idea of talking at a piece of iron and hearing another piece of iron talk seemed like a kind of witchcraft.

In the telephone we see another use of the electromagnet. A very thin iron disk near the poles of an electromagnet forms the telephone receiver (Fig. 69). An electric current travels over the telephone wire. If the current grows stronger, the magnet is made stronger and pulls the disk toward it. If the current grows weaker, the magnet becomes weaker and does not pull so hard on the disk. The disk then springs back from the magnet. If these changes take place rapidly the disk moves back and forth rapidly and gives out a sound. The sound of the voice at the other end of the line sets the disk in the mouthpiece vibrating. The vibrations of this disk cause the changes in the electric current flowing over the line-wire, and the changes in the electric current cause the disk of the receiver to vibrate in exactly the same way as the disk at the mouthpiece. Thus the words spoken into the mouthpiece may be heard at the receiver.

FIG. 69–A TELEPHONE RECEIVER FIG. 69–A TELEPHONE RECEIVER

The transmitter used by Bell was like the receiver. Two receivers from the common telephone connected by two wires may be used as a telephone without batteries. Fig. 70 shows a complete telephone made of two receivers connected by two wires. The disk in one receiver which is now used as a transmitter is made to vibrate by the sound of the voice. Now when a piece of iron moves back and forth in a magnetic field it strengthens and weakens the field. So the magnetic field in the transmitter is rapidly changed by the movement of the iron disk. Now we have found that whenever a coil of wire is in a changing magnetic field a current is induced in the coil. The small coil in the transmitter, therefore, has a current induced in it. We have also found that when the magnetic field is made stronger the induced current flows in one direction, and when the field is made weaker the current flows in the opposite direction. Since the field in the transmitter is made alternately stronger and weaker, the current in the coil flows first in one direction, then in the opposite direction—that is, we have an alternating current. This alternating current, of course, flows over the line-wire and through the coil in the receiver. In the receiver the alternating current will alternately strengthen and weaken the magnetic field, and as it does so the pull of the magnet on the iron disk is strengthened and weakened. The iron disk in the receiver, therefore, vibrates in exactly the same way as the disk in the transmitter, and so gives out a sound just like that which is acting on the transmitter.

FIG. 70–TWO RECEIVERS USED AS A COMPLETE TELEPHONE FIG. 70–TWO RECEIVERS USED AS A COMPLETE TELEPHONE

In the Blake transmitter, which is now commonly used, the disk moves a pencil of carbon which presses against another pencil of carbon. This varies the pressure between the two pencils of carbon. A battery current flows through the two carbons, and as the pressure of the carbons changes the strength of the current changes. When the carbons are pressed together more closely the current is stronger. When the pressure is less the current is weaker. We have, then, a varying current through the carbons. This current flows through the primary coil of an induction-coil, the secondary being connected to the line-wire. Now a current of varying strength in the primary induces an alternating current in the secondary. We have, then, an alternating current flowing over the line-wire. This alternating current acts on the magnetic field of the receiver in the way described before, causing the disk in the receiver to vibrate and give out the sound.

For long-distance work a carbon-dust transmitter (Fig. 71) is used. In this there are many granules of carbon, so that instead of two carbon-points in contact there are many. This makes the transmitter more sensitive.

FIG. 71–CARBON-DUST TRANSMITTER FIG. 71–CARBON-DUST TRANSMITTER

The strength of current required for the telephone is very small. To transmit a telephone message requires less than a hundred-millionth part of the current required for a telegraphic message. The work done in lifting the telephone receiver a distance of one foot, if changed into an alternating current, would be sufficient to keep up a sound in the receiver for a hundred thousand years. Because of its extreme sensitiveness the telephone requires a complete wire circuit. The earth cannot be used for the return circuit, as in the case of the telegraph. Disturbances in the earth, vibration, leakage currents from trolley lines, and so forth, would interfere seriously with the action of the telephone.

When the telephone was invented it was commonly remarked that it could not take the place of the telegraph in commerce, for the latter gave the merchant some evidence of a business transaction, while the telephone left no sign. There was a time when men feared to trust each other, but now large business deals are made by telephone; products of the farm, the factory, and the mine are bought and sold in immense quantities without a written contract or even the written evidence of a telegram. Thus the telephone has developed a spirit of business honor.

The Phonograph

The phonograph grew out of the telephone. It is said to be the only one of Edison's inventions that came by accident, yet only a man of genius would have seen the meaning of such an accident. He was singing into the mouthpiece of a telephone when the vibrations of the disk caused a fine steel point to pierce one of his fingers held just behind the disk. This set him to thinking. If the sound of his voice could cause the disk to vibrate with force enough to pierce the skin, would it not make impressions on tin-foil, and so make a record of the voice that could be reproduced by passing the point rapidly over the same impressions? He gave his assistants the necessary instructions, and soon the first phonograph was made.

This disk in the phonograph is set in vibration by sound vibrations in the air in the same way as the disk in the telephone transmitter. Attached to the disk is a needle-point which, of course, vibrates with the disk. If a cylinder with a soft surface is turned rapidly under the steel point as it vibrates, impressions are made in the cylinder corresponding to the movements of the disk. The cylinder must move forward as it turns, so that its path will be a spiral. If, now, the stylus is placed at the starting-point and the cylinder turned rapidly the stylus will move rapidly up and down as it goes over the indentations in the cylinder, and so cause the metal disk to vibrate and give out a sound like that received at first. In the earliest phonographs the cylinder was covered with tin-foil. Later the so-called "wax records" came into use. These cylinders are not made of wax, but of very hard soap. Fig. 72 shows an instrument in which the sound of the voice caused a pencil-point to trace a wavy line on a cylinder. This instrument may be called a forerunner of the phonograph. Fig. 73 shows Edison's first phonograph with a modern instrument placed beside it for comparison.

FIG. 72–THE PHONAUTOGRAPH, A FORERUNNER OF THE PHONOGRAPH FIG. 72–THE PHONAUTOGRAPH, A FORERUNNER OF THE PHONOGRAPH

FIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENT FIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENT

Photo by Claudy.

Gas-Engines

Cannons are the oldest gas-engines. Indeed, the principle of the cannon is the same as that of the modern gas-engine, the piston in the engine taking the place of the cannon-ball. The power in each case is obtained by explosion—in the cannon the explosion of powder, in the engine the explosion of a mixture of air and gas. Powder-engines with pistons were proposed in the seventeenth century, and some were actually built, but it proved too difficult to control them, and the idea of the gas-engine was abandoned for more than a hundred years.

The discovery of coal-gas near the close of the eighteenth century gave a new impetus to the gas-engine. John Barber, an Englishman, built the first actual gas-engine. He used gas distilled from wood, coal, or oil. The gas, mixed with the proper proportion of air, was introduced into a tank which he called the exploder. The mixture was fired and issued out in a continuous stream of flame against the vanes of a paddle-wheel, driving them round with great force.

In 1804 Lebon, a French engineer, was assassinated, and the progress of the gas-engine set back a number of years, for this engineer had proposed to compress the mixture of gas and air before firing, and to fire the mixture by an electric spark. This is the method used in gas-engines to-day.

The first practical working gas-engine was invented by Lenoir, a Frenchman, in 1860. From this time to the end of the century the gas-engine developed rapidly, receiving a new impulse from the increasing demand for the motor-car.

The engine of the German inventors, Otto and Langen, brought out in 1876, marked the beginning of a new era. The greater number of engines used in automobiles to-day are of the kind known as the Otto cycle, or four-cycle, engine. This engine is called four-cycle because the piston makes four strokes for every explosion. There is one stroke to admit the mixture of gas and air to the cylinder, another to compress the gas and air, at the beginning of the third stroke the explosion takes place, and in the fourth stroke the burned-out gases are driven out of the cylinder. The working of the four-cycle gas-engine is made clear in Figs. 74, 75, 76, and 77.

FIG. 74–FIRST STROKE. GAS AND AIR ADMITTED TO THE CYLINDER FIG. 74–FIRST STROKE. GAS AND AIR ADMITTED TO THE CYLINDER
FIG. 75–SECOND STROKE. MIXTURE OF GAS AND AIR COMPRESSED
FIG. 76–THIRD STROKE. THE MIXTURE IS EXPLODED AND EXPANDS, DRIVING THE PISTON FORWARD
FIG. 77–FOURTH STROKE, EXHAUST. THE BURNED-OUT MIXTURE OF GAS AND AIR EXPELLED FROM THE CYLINDER

THE FOUR-CYCLE GAS-ENGINE

In such a gas-engine the power is applied to the piston only in one stroke out of every four, while in the steam-engine the power is applied at every stroke. It would seem, therefore, that a steam-engine would do more work than a gas-engine for the same amount of heat, but such is not the case; in fact, a good gas-engine will do about twice as much work as a good steam-engine for the same amount of fuel. The reason is that the steam-engine wastes its heat. Heat is given to the condenser, to the iron of the boiler, to the connecting pipes and the air around them, while in the gas-engine the heat is produced in the cylinder by the explosion and the power applied directly to the piston-head. More than this, a steam-engine when at rest wastes heat; there must be a fire under the boiler if the engine is to be ready for use on short notice. When a gas-engine is at rest there is no fire, nothing is being used up, and yet the engine can be started very quickly. A gas-engine can be made much lighter than a steam-engine of the same horse-power. The automobile and the flying-machine require very light engines. Without the gas-engine the automobile would have remained imperfect and crude, while the flying-machine would have been impossible.

In a two-cycle gas-engine there is an explosion for every two strokes of the piston, or one explosion for every revolution of the crank-shaft. During one stroke the mixture of gas and air on one side of the piston is compressed and a new mixture enters on the opposite side of the piston. At the end of this stroke the compressed mixture is exploded, and power is applied to the piston during about one-fourth of the next stroke. During the remainder of the second stroke the burned-out gas escapes, and the fresh mixture passes over from one side of the piston to the other ready for compression. The two-cycle engine is simpler in construction than the four-cycle, having no valves. It also has less weight per horse-power. The cylinder of a two-cycle engine is shown in Fig. 78.

FIG. 78–TWO-CYCLE GAS-ENGINE. CRANK AND CONNECTING-ROD ARE ENCLOSED WITH THE PISTON FIG. 78–TWO-CYCLE GAS-ENGINE. CRANK AND CONNECTING-ROD ARE ENCLOSED WITH THE PISTON

A steam-engine is self-starting. The engineer has only to turn the steam into the cylinder, but the gas-engine requires to be turned until at least one explosion takes place, for until there is an explosion of gas and air in the cylinder there is no power.

A gas-engine may have a number of cylinders. Four-cylinder and six-cylinder engines are common. In a four-cylinder, four-cycle engine, while one cylinder is on the power stroke the next is on the compression stroke, the third on the admission stroke, and the fourth on the exhaust stroke. Fig. 79 shows the Selden "explosion buggy" propelled by a gas-engine. This machine was the forerunner of the modern automobile.

FIG. 79–SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE MODERN AUTOMOBILE FIG. 79–SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE MODERN AUTOMOBILE

The Steam Locomotive

Late in the eighteenth century a mischievous boy put some water in a gun-barrel, rammed down a tight wad, and placed the barrel in the fire of a blacksmith's forge. The wad was thrown out with a loud report, and the boy's play-mate, Oliver Evans, thought he had discovered a new power. The prank with the gun-barrel set young Evans thinking about the power of steam. It was not long until he read a description of a Newcomen engine. In the Newcomen engine, you will remember, it was the pressure of air, not the pressure of steam, that lifted the weight. Evans soon set about building an engine in which the pressure of steam should do the work. He is sometimes called the "Watt of America," for he did in America much the same work that Watt did in Scotland. Evans built the first successful non-condensing engine—that is, an engine in which the steam, after driving the piston, escapes into the air instead of into a condenser. The non-condensing engine made the locomotive possible, for a locomotive could not conveniently carry a condenser. Evans made a locomotive which travelled very slowly. He said, however: "The time will come when people will travel in stages moved by steam-engines from one city to another, almost as fast as birds can fly, fifteen or twenty miles an hour."

The inventor who made the first successful locomotive was George Stephenson, and it is worth noting that one of his engines, the "Rocket," possessed all the elements of the modern locomotive. He combined in the "Rocket" the tubular boiler, the forced draft, and direct connection of the piston-rod to the crank-pin of the driving-wheel.

The "Rocket" was used on the first steam railway (the Stockton & Darlington, in England), which was opened in 1825. There had been other railways for hauling coal by means of horses over iron tracks, and other locomotives that travelled over an ordinary road; but this was the first road on which a steam-engine pulled a load over an iron track, the first real railroad. Fig. 80 shows the "Rocket" and two other early locomotives.

FIG. 80–SOME EARLY LOCOMOTIVES FIG. 80–SOME EARLY LOCOMOTIVES

The one on the right is Stephenson's "Rocket."

Photo by Claudy.

In order to build a railroad between Liverpool and Manchester for carrying both passengers and freight it was necessary to secure an act of Parliament. Stephenson was compelled to undergo a severe cross-examination by a committee of Parliament, who feared there would be great danger if the speed of the trains were as high as twelve miles an hour. He was asked:

"Have you seen a railroad that would stand a speed of twelve miles an hour?"

"Yes."

"Where?"

"Any railroad that would bear going four miles an hour. I mean to say that if it would bear the weight at four miles an hour it would bear it at twelve."

"Do you mean to say that it would not require a stronger railway to carry the same weight at twelve miles an hour?"

"I will give an answer to that. I dare say every person has been over ice when skating, or seen persons go over, and they know that it would bear them better at a greater velocity than it would if they went slower; when they go quickly the weight, in a measure, ceases."

"Would not that imply that the road must be perfect?"

"It would, and I mean to make it perfect."

For seven miles the road must be built over a peat bog into which a stone would sink to unknown depths. To convince the committee, however, and secure the act of Parliament was more difficult than to build the road. But Stephenson was one of the men who do things because they never give up, and the road was built.

How a Locomotive Works

To understand how a locomotive works, let us consider how the steam is produced, how it acts on the piston, and how it is controlled. The steam is produced in a locomotive in exactly the same way that steam is produced in a tea-kettle. Now everybody knows that a quart of water in a tea-kettle with a wide bottom placed on a stove will boil more quickly than the same amount of water in a tea-pot with a narrow bottom. The greater the heating-surface—that is, the greater the surface of heated metal in contact with the water—the more quickly the water will boil and the more quickly steam can be produced. In a locomotive the aim is to use as large a heating-surface as possible. This is done by making the fire-box double and allowing the water to circulate in the space between the inner and outer parts, except underneath; also by placing tubes in the boiler through which the heated gases and smoke from the fire must pass. An ordinary locomotive contains two hundred or more of these tubes. The water surrounds these tubes, and is therefore in contact with a very large surface of heated metal. In some engines the water is in the tubes, and the heated gases surround the tubes.

The steam as it enters the cylinder should be dry—that is, it should not contain drops of water. This is accomplished by allowing the steam from the boiler to pass into a dome above the boiler. Here the steam, which is nearly dry, enters a steam-pipe leading to the cylinder (Fig. 81). The steam is admitted to the cylinder by means of a slide-valve. From the diagram it can easily be seen that the valve admits steam first on one side of the piston, then on the other. It can also be seen that the valve closes the admission-port, and so cuts off the steam before the piston has made a full stroke. The steam that is shut up in the cylinder continues to expand and act on the piston. At the same time the valve opens the exhaust-port, allowing the steam to escape from the other side of the piston; but it closes this port before the piston has quite finished the stroke. The small quantity of steam thus shut up acts like a cushion to prevent the piston striking the end of the cylinder with too great force. The exhaust-steam escapes through a blast-pipe into the chimney, drives the air before it up the chimney, and thus makes a greater draft of air through the fire-box. This is called the forced draft. The escape of the exhaust-steam causes the puffing of the locomotive just after starting. After the engine is under way the engineer partly shuts off the steam by means of the reversing lever and the puffing is less noticeable.

FIG. 81–HOW A LOCOMOTIVE WORKS FIG. 81–HOW A LOCOMOTIVE WORKS

The arrows show the course of the steam.

The action of the steam may be summed up as follows:

1. Steam admitted to the cylinder (admission).

2. Valve closes admission-port (cut-off).

3. Steam shut up in the cylinder expands, acting on the piston (expansion period).

4. Valve opens exhaust-port to allow used steam to escape (exhaust).

The devices for controlling the steam are the throttle-valve and the valve-gear. The throttle-valve is at the entrance to the steam-pipe in the steam-dome. This valve is opened and closed by means of a rod in the engineer's cab.

Stephenson's link-motion valve-gear is used on most locomotives. The forward rod in the diagram is in position to act upon the valve-rod through the lever L. Suppose the reversing-lever is drawn back to the dotted line; then the forward rod will be raised and the backward rod will come into position to act on the lever L. If this is done while the locomotive is at rest the valve is moved through one-half a complete stroke. In the diagram the steam enters the cylinder on the right of the piston. After this movement of the valve the steam would enter on the left side of the piston. In the present position the locomotive would move forward, but if the valve is changed so as to admit steam to the left of the piston while the connecting-rod is in the position shown then the engine will move backward. Thus the direction can be controlled by the engineer in the cab. Of course, this can be done while the engine is in motion. The forward rod and the backward rod are each moved by an eccentric on the axle of the front driving-wheel. The two eccentrics are in opposite positions on the axle. An eccentric acts just like a crank, causing the rod to move forward and backward as the axle turns, and of course this motion is given to the valve-rod through the lever. When the link is set midway between the forward and the backward rod the valve cannot move. When the link is raised or lowered part way the valve makes a short stroke, and less steam is admitted to the cylinder than with a full stroke. In starting the locomotive the valve is set to make a full stroke. When the train is under headway the valve is set for a short stroke to economize steam. The valve-gear and the throttle-valve together take the place of the governor in the stationary engine, but while the governor acts automatically these are controlled by the engineer.

In reality a locomotive is two engines, one on either side, connected to the same driving-wheels. But the two piston-rods are connected to the driving-wheels at points which are at right angles with each other, so that when the crank on one side is at the end of a stroke—the "dead centre"—that on the other side is on the quarter, either above or below the axle, ready for applying the greatest turning force.

The expansion-engine was designed to use more of the power of the steam than can be done in the single-cylinder engine. In the double expansion-engine the steam expands from one cylinder into another. The second cylinder must be larger in diameter than the first. In the triple expansion-engine the steam expands from the second cylinder into a third, still larger. The second and third cylinders use a large part of the power that would be wasted with only one cylinder.

The Turbine

One of the great inventions relating to steam-power is the steam-turbine. The water-turbine is equally useful in relation to water-power. The water-turbine and the steam-turbine work in very much the same way, the difference being due to the fact that steam expands as it drives the engine, while water drives it by its weight in falling, or by its motion as it rushes in a swift stream or jet against the blades of the turbine.

The first steam-engine, that of Hero in the time of Archimedes, was a form of turbine (Fig. 82). It was driven by the reaction of the steam as it escaped into the air. The common lawn-sprinkler, that whirls as the water rushes through it, is a water-turbine that works in the same way. "Barker's Mill" is the name applied to a water-turbine that works like the lawn-sprinkler. As the water rushes out of the opening it pushes against the air. It cannot push against the air without pushing back at the same time. Never yet has any person or object in nature been able to push in one direction only. It cannot be done. If you push a cart forward you push backward against the ground at the same time. If there were nothing for you to push back against your forward push would not move the cart a hair's-breadth. If you doubt this, try to push a cart when you are standing on ice so slippery that you cannot get a foothold. It is the backward push of the water in the lawn-sprinkler and the backward push of the steam in Hero's engine that cause the machine to turn.

FIG. 82–HERO'S ENGINE FIG. 82–HERO'S ENGINE

The turbines in common use for both water and steam power have curved blades. The reason for curving the blades can best be seen by referring to an early form of water-wheel. The best water-turbine is only an improved form of water-wheel. The first water-wheels had flat blades, and these answered very well so long as only a low power was needed and it was not necessary to save the power of the water. It was found, however, that there was a great waste of power in the wheel with flat blades. One inventor proposed to improve the wheel by curving the blades in such a way that the water would glide up the curve and then drop directly downward (Fig. 83). The water then gives up practically all of its power to the wheel and falls from the wheel. It would have no power to move a second wheel. In this way he used practically all the power of the water. To save the power of the water by making all of the water strike the wheel at high speed the channel was made narrow just above the wheel, forming a mill-race. This applies to the undershot wheel. In the overshot wheel (Fig. 84) the power depends on the weight of the water and on its height. The water runs into buckets attached to the wheel, and, as it falls in these buckets, turns the wheel. The undershot wheel and the mill-race represent a common form of turbine, that form in which the steam or the water is forced in a jet against a set of curved blades. Fig. 85 shows a steam-turbine run by a jet of steam. In the water-turbine there are two sets of blades. One set rotates, the other remains fixed. The use of the fixed blades is to turn the water and drive it in the right direction against the moving blades. In some forms of turbine there are more than two sets of blades. The steam, as it passes through, gives up some of its power to each set of blades until, after passing the last set, it has given up nearly all its power. The action of the steam in this turbine is somewhat like that in the expansion-engine, in which the steam gives up a portion of its power in each cylinder. Fig. 86 is from a photograph of a modern steam-turbine, and Fig. 87 is a drawing of the same turbine showing the course of the steam. Fig. 88 is a turbine that runs a large dynamo.

FIG. 83–AN UNDERSHOT WATER-WHEEL WITH CURVED BLADES FIG. 83–AN UNDERSHOT WATER-WHEEL WITH CURVED BLADES

FIG. 84–AN OVERSHOT WATER-WHEEL FIG. 84–AN OVERSHOT WATER-WHEEL

FIG. 85–DE LAVAL STEAM-TURBINE FIG. 85–DE LAVAL STEAM-TURBINE

Driven by a jet of steam striking the blades.

FIG. 86–A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADES FIG. 86–A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADES

FIG. 87–DIAGRAM OF TURBINE SHOWN IN FIG. 86 FIG. 87–DIAGRAM OF TURBINE SHOWN IN FIG. 86

The arrows show the course of the steam.

FIG. 88–A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWER FIG. 88–A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWER

The steam enters through the large pipe at the left.

In 1897, as the battle-ships of the British fleet were assembled to celebrate the Diamond jubilee of Queen Victoria, a little vessel a hundred feet long darted in and out among the giant ships, defied the patrol-boats whose duty it was to keep out intruders, and raced down the lines of battle-ships at the then unheard-of speed of thirty-five knots an hour. It was the Turbinia, fitted with the Parsons turbine. This event marked the beginning of the modern turbine. It also marked the beginning of a revolution in steam propulsion.

The Parsons turbine does not use the jet method, but the steam enters near the centre of the wheel and flows toward the rim, passing over a number of rows of curved blades. The Parsons turbine is used on the fastest ocean liners. The Lusitania, one of the fastest steamships in the first decade of the twentieth century, has two sets of high and low pressure turbines with a total of 68,000 horse-power.

The windmill is a form of turbine driven by the air. As the air rushes against the blades of the windmill, it forces them to turn. If the windmill were turned by some mechanical power, it would drive the air back, and we should have a blower. This is what we have in the electric fan, a small windmill driven by an electric motor so that it drives the air instead of being driven by it. The blades of the windmill and the electric fan are shaped very much like the screw propeller. The screw propeller, driven by an engine, would drive the water back if the ship were firmly anchored, just as the fan drives the air. But it cannot drive the water back without pushing forward on the ship at the same time, and this forward push propels the ship. It is difficult to attain what is now regarded as high speed with a single screw. With engines in pairs and two lines of shafting higher power can be used. The best steamers, therefore, are fitted with the twin-screw propeller. Some large steamers have three and some four screws.

The screw propellers of turbine steamships are made of small diameter, that they may rotate at high speed without undue waste of power. By the use of turbine engines and twin-screw propellers, the weight of the machinery has been greatly reduced. The old paddle-wheels, with low-pressure engines, developed only about two horse-power for each ton of machinery. The turbine, with the twin-screw propeller, develops from six to seven horse-power for every ton of machinery. The modern steamer, with all its machinery and coal for an Atlantic voyage, weighs no more than the engines of the old paddle-wheel type and coal would weigh for the same horse-power. The steam-turbine and the twin-screw propeller have made rapid ocean travel possible.

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