FIG. 57–FIRST COMMERCIAL ELECTRIC RAILWAYFIG. 57–FIRST COMMERCIAL ELECTRIC RAILWAYAn old horse-car converted into an electric car.Electric LightingFrom 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 ineach 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 glowedmore 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 kindof 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 steamshipColumbiain 1880.FIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORYFIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORYCopyright, 1904, by Byron, N. Y.FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870Copyright, 1904, by William J. HammerFIG. 60–FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880FIG. 60–FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880The 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 toa 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 TelegraphThe 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 currentfor 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-shipSully, 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 throughthe 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.FIG. 61–A TELEGRAPH SOUNDERFIG. 61–A TELEGRAPH SOUNDERFIG. 62–MORSE'S FIRST TELEGRAPH INSTRUMENTFIG. 62–MORSE'S FIRST TELEGRAPH INSTRUMENTA 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 thelocal 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 SOUNDERFIG. 63–A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDERIn the telegraphic circuit only one connecting wire isneeded. 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 CIRCUITFIG. 64–A SIMPLE TELEGRAPHIC CIRCUITTwo keys are shown atK K, and two switches atS 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 inBaltimore, 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 WORKFIG. 65–FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL WORKPhoto 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 neededsuch 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 TelegraphyThe 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 southpole. 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 TIMEFIG. 66–HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIMEAnother method not quite so simple in principle is the bridge method. When the key at stationA(see Fig. 67) is closed, the current from the battery at stationAdivides atC, and if the resistances1and2are equal, and the resistance3is 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 atD, 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 METHODFIG. 67–HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME. BRIDGE METHODThe 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 TelephoneThe 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 releasesthe 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 vibratea 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 makingsome 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 TRANSMITTERFIG. 68–FIRST BELL TELEPHONE RECEIVER AND TRANSMITTERThe 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 growsstronger, 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 RECEIVERFIG. 69–A TELEPHONE RECEIVERThe 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 strongerand 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 TELEPHONEFIG. 70–TWO RECEIVERS USED AS A COMPLETE TELEPHONEIn 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 TRANSMITTERFIG. 71–CARBON-DUST TRANSMITTERThe 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 PhonographThe 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 diskcaused 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 PHONOGRAPHFIG. 72–THE PHONAUTOGRAPH, A FORERUNNER OF THE PHONOGRAPHFIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENTFIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENTPhoto by Claudy.Gas-EnginesCannons 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. Heused 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 CYLINDERFIG. 74–FIRST STROKE. GAS AND AIR ADMITTED TO THE CYLINDERFIG. 75–SECOND STROKE. MIXTURE OF GAS AND AIR COMPRESSEDFIG. 76–THIRD STROKE. THE MIXTURE IS EXPLODED AND EXPANDS, DRIVING THE PISTON FORWARDFIG. 77–FOURTH STROKE, EXHAUST. THE BURNED-OUT MIXTURE OF GAS AND AIR EXPELLED FROM THE CYLINDERTHE FOUR-CYCLE GAS-ENGINEIn 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 freshmixture 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 PISTONFIG. 78–TWO-CYCLE GAS-ENGINE. CRANK AND CONNECTING-ROD ARE ENCLOSED WITH THE PISTONA 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" propelledby a gas-engine. This machine was the forerunner of the modern automobile.
FIG. 57–FIRST COMMERCIAL ELECTRIC RAILWAYFIG. 57–FIRST COMMERCIAL ELECTRIC RAILWAYAn old horse-car converted into an electric car.
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 ineach 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 glowedmore 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 kindof 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 steamshipColumbiain 1880.
FIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORYFIG. 58–EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORYCopyright, 1904, by Byron, N. Y.
Copyright, 1904, by Byron, N. Y.
FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870FIG. 59–EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870Copyright, 1904, by William J. Hammer
Copyright, 1904, by William J. Hammer
FIG. 60–FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880FIG. 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 toa 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 currentfor 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-shipSully, 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 throughthe 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.
FIG. 61–A TELEGRAPH SOUNDERFIG. 61–A TELEGRAPH SOUNDER
FIG. 62–MORSE'S FIRST TELEGRAPH INSTRUMENTFIG. 62–MORSE'S FIRST TELEGRAPH INSTRUMENTA 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.
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 thelocal 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 SOUNDERFIG. 63–A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDER
In the telegraphic circuit only one connecting wire isneeded. 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 CIRCUITFIG. 64–A SIMPLE TELEGRAPHIC CIRCUITTwo keys are shown atK K, and two switches atS S. When one key is to be used the switch at that station must be open, and the switch at the other station closed.
Two keys are shown atK K, and two switches atS 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 inBaltimore, 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 WORKFIG. 65–FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL WORKPhoto by Claudy.
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 neededsuch 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 southpole. 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 TIMEFIG. 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 stationA(see Fig. 67) is closed, the current from the battery at stationAdivides atC, and if the resistances1and2are equal, and the resistance3is 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 atD, 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 METHODFIG. 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 releasesthe 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 vibratea 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 makingsome 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 TRANSMITTERFIG. 68–FIRST BELL TELEPHONE RECEIVER AND TRANSMITTERThe 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 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 growsstronger, 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 RECEIVERFIG. 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 strongerand 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 TELEPHONEFIG. 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 TRANSMITTERFIG. 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 diskcaused 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 PHONOGRAPHFIG. 72–THE PHONAUTOGRAPH, A FORERUNNER OF THE PHONOGRAPH
FIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENTFIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENTPhoto by Claudy.
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. Heused 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 CYLINDERFIG. 74–FIRST STROKE. GAS AND AIR ADMITTED TO THE CYLINDERFIG. 75–SECOND STROKE. MIXTURE OF GAS AND AIR COMPRESSEDFIG. 76–THIRD STROKE. THE MIXTURE IS EXPLODED AND EXPANDS, DRIVING THE PISTON FORWARDFIG. 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 freshmixture 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 PISTONFIG. 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" propelledby a gas-engine. This machine was the forerunner of the modern automobile.