If an electric arc is enclosed by something that will hold the heat in we have an electric furnace, and any substance placed in the furnace may be made nearly as hot as the arc itself. In the electric furnace any substance, whether found in nature or prepared artificially, may be melted or vaporized.
It was Henri Moissan, Professor of Chemistry at the Sorbonne in Paris, who made the first great discoveries in the use of the electric furnace and produced the first artificial diamonds. The study of diamonds led Moissan to believe that in nature they are formed by the cooling of a melted mixture of iron and carbon. He could prepare such a mixture with his electric furnace, he thought, and so make diamonds like those of the diamond mines. So, with an electric furnace having electrodes as large as a man"s wrist, a mixture of iron and charcoal in a carbon crucible, and a gla.s.s tank filled with water, Moissan set out to change the charcoal to diamonds. At a temperature of more than six thousand degrees the iron and charcoal were melted together. For a time of from three to six minutes the mixture was in the intense heat. Then the covering of the furnace was removed and the crucible with the melted mixture dropped into the tank of water. With some fear this was done for the first time, for it was not known what would happen when such a hot object was dropped into cold water. But no explosion occurred, only a violent boiling of the water, a fierce blazing of the molten ma.s.s, and then a gradual change of color from white to red and red to black. With boiling acids and other chemicals the refuse was removed, and the fragments that remained were found to be diamonds, small, it is true, so small that they could be seen only with the aid of a microscope, but giving promise of greater things to come. The outer crust of iron held the melted charcoal under enormous pressure while it slowly cooled and formed the diamond crystals. The process of manufacturing diamonds is ill.u.s.trated in Figs. 105, 106, and 107.
[Ill.u.s.tration: FIG. 105--MANUFACTURING DIAMONDS--FIRST OPERATION Preparing the furnace. Charcoal and iron ore placed in a crucible and subjected to enormous heat electrically.]
[Ill.u.s.tration: FIG. 106--MANUFACTURING DIAMONDS--SECOND OPERATION The furnace at work.]
[Ill.u.s.tration: FIG. 107--MANUFACTURING DIAMONDS--THIRD OPERATION Plunging the crucible into cold water. Observe the white-hot carbon just removed from the furnace.]
The electric furnace has made possible the preparation of substances unknown before, and the production in large quant.i.ties at low cost of substances that before were too costly for general use. One of the best known of these substances is aluminum. With the discovery of the electric-furnace method of extracting aluminum from its ores, the price of aluminum fell from one hundred and twenty-four dollars per pound to twelve cents per pound.
Among the many uses of the electric furnace we may mention the preparation of calcium carbide, which is used in producing the acetylene light; carborundum, a substance almost as hard as diamond; and phosphorus, which is used in making the phosphorus match. It is used also to some extent in the manufacture of gla.s.s, and, in some cases, for extracting iron from its ores.
The Wireless Telegraph
A ship in a fog is struck by another ship. The water rushes in, puts out the fires in the boilers, the engines stop, the ship is helpless in mid-ocean in the darkness of the night. But the snapping of an electric spark is heard in one of the cabins. Soon another vessel steams alongside. The life-boats are lowered and every person is saved. The call for help had gone out over the sea in every direction for two hundred miles. Another ship had caught the signal and hastened to the rescue, and the world realized that the wireless telegraph had robbed the sea of its terrors.
Without the curious combination of magnets, wires, and batteries on the first ship no signal could have been sent, and without such a combination on the second ship the signal would have pa.s.sed unheeded.
How was this combination discovered, and how does it work?
Faraday, as we have seen, discovered the principle of the induction-coil. With the induction-coil a powerful electric spark can be produced. The friction electrical machine was known long before the time of Faraday. Franklin proved that a stroke of lightning is like a spark from an electrical machine, only more powerful. These great discoverers did not know, however, that an electric spark sends out something like light which travels in all directions. They did not know it, because they had no eyes to see this strange light.
I will tell you a fable to make the meaning clear. There once lived a race of blind men. Not one of them could see. They built houses and cities, railroads and steamships, but they did everything by touch and sound. When they met they touched each other and spoke, and each man knew his friend by the sound of his voice. One day a wise man among them said he believed there was something besides the sound of the voice with which they could make signals to each other. Another wise man thought upon this matter for some time and brought forth a proof that there is something called light, though no man could see it. Another, wiser and more practical, invented an eye which any man could carry about with him and see the light when he turned it in the direction from which the light was coming. Thereafter each man carried a light that flashed like the flashing of a firefly. Each man also carried an eye, and each could see his friend as well as hear the sound of his voice.
The fable is true. The light which no man had seen we now call electric waves. The eye with which any one can perceive this light is the receiving instrument of the wireless telegraph. The strange light flashed out whenever an electric spark pa.s.sed from an electrical machine, a Leyden jar, an induction-coil, or as lightning in the clouds, but for hundreds of years this light was unseen. The human eye could not see it, and no artificial eye that would catch electric waves had been invented. A man in England, James Clerk-Maxwell, first proved that there is such a light. Heinrich Hertz, a German, first made an eye that would catch the waves from the electric spark, and the man who first perfected an eye with which one could catch the electric waves at a great distance and improved the instruments for sending out such waves was Marconi.
The fable is true, for electric waves are like the light from the sun.
They go through s.p.a.ce in all directions as light does. They will not merely go through air, but through what we call empty s.p.a.ce, or a vacuum, as light will. If we think of waves somewhat like water waves, but not exactly like them, rushing through s.p.a.ce, we have about as good a picture of electric waves as we can well form in our minds. As the light of a lamp goes out in all directions, so do the electric waves go out in all directions from the place where the electric spark pa.s.ses.
Since these waves go through what we call empty s.p.a.ce, we must think of something in that s.p.a.ce and that it is not really empty. Examine an incandescent electric lamp. The bulb was full of air when the carbon thread was placed in it. The air was then pumped out until only about a millionth part remained. The bulb was then sealed at the tip and made air-tight. We say the s.p.a.ce inside is a vacuum. If the bulb is broken there is a loud report as the air rushes in. Is the bulb really empty after the air is pumped out? Is anything left in the bulb around the carbon thread? Turn on the electric current and the carbon thread becomes white hot. The light from the white-hot carbon thread goes out through the vacuum. There is nothing in the vacuum that we can see or feel or handle, but something must be there to carry the light from the carbon thread. The light of the sun comes to the earth through ninety-three million miles of s.p.a.ce. Is there anything between the earth and the sun through which this light can pa.s.s? Light, we know, is made up of waves, and we cannot think of waves going through empty s.p.a.ce.
There must be something between the sun and the earth. That something through which the light of the sun comes to the earth we call the ether.
It is the ether that carries the light across the vacuum in the light bulb as well as from the sun to the earth. Electric waves used in wireless telegraphy go through this same ether. The light of the sun is made up of the same kind of waves, and we do not think it strange because it is so common. It is true we do not see light waves, but they affect our eyes so that by means of them we can see objects and perceive the flashing of a light. So with the wireless receiving instrument we do not see the electric waves, but we perceive the flashing of the strange light. Electric waves and light travel with the same speed--186,000 miles in a second. A wireless message will go around the earth in about one-seventh of a second.
Electric waves will go through a brick wall as readily as sunlight will go through a gla.s.s window, but that is not so strange as it may seem.
Red light will not go through blue gla.s.s. Blue gla.s.s holds back the red light, but lets the blue light go through. So the brick wall holds back common light, but allows the light which we call electric waves to go through.
Some waves on water are longer than others. So electric waves are longer than light waves. That is the only difference between them. In fact, the light of the sun is made up of very short electric waves. These short waves affect our eyes, but the longer electric waves do not. We are daily receiving the wireless-telegraph waves from the sun, which we call light. Electric waves used in wireless telegraphy vary from about six hundred feet to two miles in length, while the longest light waves that affect our eyes are only one thirty-three-thousandth of an inch in length.
The sensitive part of the Marconi receiving apparatus is the coherer.
The first coherer was made in 1890 by Prof. Edward Branly, of the Catholic University of Paris. Very fine metal filings were enclosed in a tube of ebonite and connected in a circuit with a battery and a galvanometer. The filings have so high a resistance that no current flows. The waves from an electric spark, however, affect the filings so that they allow the current to flow. The electric waves are said to cause the filings to cohere--that is, to cling together more closely. It is a peculiar form of electric welding. Branly discovered that a slight tapping of the tube loosens the filings and stops the flow of the current.
All that was needed for wireless telegraphy was at hand. Men knew how to produce electric waves of any desired length. They knew how they would act. A sensitive receiver had been discovered. There was needed the practical man who should combine the parts, improve details, and apply the wireless telegraph to actual use. This was the work of Guglielmo Marconi. In 1894, at the age of twenty, Marconi began his experiments on his father"s estate, the Villa Grifone, Bologna, Italy. Fig. 108 is from a photograph of Marconi and his wireless sending and receiving instruments.
[Ill.u.s.tration: FIG. 108--MARCONI AND HIS WIRELESS-TELEGRAPH SENDING AND RECEIVING INSTRUMENTS]
To Marconi, telegraphing through s.p.a.ce without wires appears no more wonderful than telegraphing with wires. In the wire telegraph electric waves, which we then call an electric current, follow a wire somewhat as the sound of the voice goes through a speaking-tube. In the wireless telegraph the electric waves go out through s.p.a.ce without any wire to guide them. The light and heat waves of the sun travel to us through millions of miles of s.p.a.ce without requiring any conducting wire. That electric waves should go though s.p.a.ce in the same way that light does is no more wonderful than that the waves should follow all the turns of a wire.
The sending instrument used by Marconi includes an induction-coil, one side of the spark-gap being connected to the earth and the other to a vertical wire (Fig. 109). There must be a battery of Leyden jars in the circuit of the secondary coil. The induction-coil may be operated by a storage battery or dynamo. The vertical wire, or antenna, is to the sending instrument what the sounding-board is to a violin. It is needed to increase the strength of the waves. In the wireless telegraph some wires must be used. It is called wireless because the stations are not connected by wires. The antenna for long-distance work consists of a network of overhead wires. When the key is pressed a rapid succession of sparks pa.s.ses across the spark-gap. The antenna, or overhead wire, is thus made to send out electric waves. By pressing the key for a longer or shorter time, a longer or shorter series of waves may be produced and a correspondingly longer or shorter effect on the receiver. In this manner the dots and dashes of the Morse alphabet may be transmitted.
[Ill.u.s.tration: FIG. 109--DIAGRAM OF WIRELESS-TELEGRAPH SENDING APPARATUS]
At the receiving station there are two circuits. One includes a coherer, a local battery, and a telegraph relay (Fig. 110). The other circuit, which is opened and closed by the relay, includes a recording instrument and a tapper. One end of the coherer is connected to the earth and the other to a vertical wire like that used for the transmitter. The electric waves weld the filings in the coherer, and this closes the first circuit. The relay then closes the second circuit, the recording instrument records a dot or a dash, and the tapper strikes the coherer and breaks the filings apart ready for another stream of electric waves.
[Ill.u.s.tration: FIG. 110--DIAGRAM OF MARCONI WIRELESS-TELEGRAPH RECEIVING APPARATUS The second circuit described in the text is not shown here. The relay and the second circuit would take the place of the electric bell. In the circuit as shown here the electric waves would cause the coherer to close the circuit and ring the bell.]
With this arrangement it was possible to work only two stations at one time. Though stations were to be established in all the cities of Great Britain, only one message could be sent at one time, and all stations but one must keep silence, because a second series of waves would mingle with the first and confusion would result.
Marconi"s next effort was to make it possible to send any number of messages at one time. This led to his system of tuning the sending and receiving instruments. With this system the receiving instrument will take a message only from a sending instrument with which it is in tune.
It is possible, therefore, for any number of wireless-telegraph stations to operate at the same time, the waves crossing one another in all directions without interfering, each receiver responding to the waves intended for it. An ocean steamer can, with the tuned system, send one message and receive another from a different station at the same time.
Marconi"s ambition was to send a wireless message across the Atlantic.
Quietly he made his preparation, building at Poldhu, Cornwall, England, a more powerful transmitter than had yet been used. At noon on the 12th of December, 1901, he sat in a room of the old barracks on Signal Hill, near St. Johns, Newfoundland, waiting for a signal from England. His a.s.sistants at the Poldhu station were to telegraph across the ocean the letter "S" at certain times each day. On the table was the receiving apparatus, made very sensitive, and including a telephone receiver. A wire led out of the window to a huge kite, which the furious wind held four hundred feet above him. One kite and a balloon used for supporting the antenna had been carried out to sea. He held the telephone receiver to his ear for some time. The critical time had come for which he had worked for years, for which his three hundred patents had prepared the way, and for which his company had erected the costly power station at Poldhu. Calmly he listened, his face showing no sign of emotion.
Suddenly there sounded the sharp click of the tapper as it struck the coherer. After a short time Marconi handed the telephone receiver to his a.s.sistant. "See if you can hear anything," he said. A moment later, faintly and yet distinctly, came the three little clicks, the dots of the letter "S" tapped out an instant before in England. Marconi"s victory was won.
A flying-machine can be equipped with a wireless-telegraph outfit, so that a man can telegraph while flying through the air. Two men are needed, one to operate the flying-machine, the other to send the telegraphic messages. This has been done with the Wright machine and with some dirigible balloons. Of course, the wireless instruments on the flying-machine cannot be connected to the ground. Instead of the ground connection there is a second antenna.--one antenna on each side of the spark-gap. While in the ordinary wireless instruments the discharge surges back and forth between the antenna and the earth, in the flying-machine wireless the discharge surges back and forth between the two antennae. In the Wright machine, when equipped for wireless telegraphy, the two antennae are placed one under the upper plane, the other under the lower plane of the flying-machine.
More power is required for the wireless than for the wire telegraph. In the wire telegraph about one-hundredth horse-power is required to send a message one hundred and twenty miles. To send a message the same distance with the wireless requires about ten horse-power, or a thousand times as much as with the wire telegraph. This is because in the wireless telegraph the waves go out in all directions, and much of the power is wasted. In the wire telegraph the electric waves are directed along the wire and very little of the power is wasted. For the same reason a person"s voice can be heard a long distance through a speaking-tube. The speaking-tube guides the sound and prevents it from scattering somewhat as the wire guides the electric waves.
The overhead wires of a wireless-telegraph station send out a "dark"
light while a message is being sent. (See frontispiece.) Standing near the station on a dark night one can see nothing, but can hear only the terrific snapping of the electric discharge. The camera, however, shows that light goes out from the wires. It is light of shorter waves than any that the eye can perceive, but the sensitive film of the photographic plate makes it known to us.
The Wireless Telephone
In sending a message by the wire telegraph the current flows over the line wire when the key is pressed. When the key is released the current stops. The circuit is made and broken for every dot or dash. This we may call an interrupted current. Now we have seen that the attempt to invent a wire telephone using an interrupted current failed. While one is talking over the wire telephone a current (alternating) must be flowing over the line wire. The sound of the voice does not make and break the circuit, but changes the strength of the current. This alternating current is wonderfully sensitive. It can vary in the rate at which it alternates or the number of alternations per second to correspond to sound of every pitch. It varies in strength to correspond to all the variations in the voice, and reproduces in the receiver not merely the words that are spoken but the quality of the voice, so that the voice of a friend can be recognized by telephone almost as well as if talking face to face.
The same things are true of the wireless telegraph and telephone.
Instead of an electric current, let us say "a stream of electric waves."
Then we may say of the wireless everything that we have said of the wire telegraph and telephone. In sending a message by wireless telegraph the stream of electric waves flows when the key is pressed and stops when the key is released. We have an interrupted stream of electric waves.
But an interrupted stream of waves cannot be used for a wireless telephone any more than an interrupted current can be used for a wire-telephone. There must be a constantly flowing stream of electric waves, and these waves must be changed in strength and form by the sound of the voice. Fig. 111 shows a wireless-telephone receiver in which light is used to carry the message. The light acts on the receiver in such a way as to reproduce the sound.
[Ill.u.s.tration: FIG. 111--RECEIVER OF BELL"S PHOTOPHONE An early idea in wireless telephony.]
In the wireless-telegraph receiver the interrupted stream of electric waves makes and breaks the circuit of an electric battery. The wireless-telephone receiver must not make and break a circuit, but it must be sensitive to all the changes in the electric waves. One such receiver is the audion, which we shall now describe.
The audion was invented by Dr. Lee de Forest. De Forest had taken the degree of Doctor of Philosophy at Yale University, having written his thesis for that degree on the subject of electric waves. He then entered the employ of the Western Electric Company in Chicago, and while in this position worked at night in his room on experiments with electric waves.
Here he found that a gas flame is sensitive to electric waves (Fig.
112). If a gas flame is made part of the circuit of an electric battery, which includes also an induction-coil connected to a telephone receiver, then when a stream of electric waves comes along there is a click in the receiver. The waves change the resistance of the flame, and so change the strength of the current. The flame is a simple audion. It is the heated gas in the flame that responds to the electric waves.
[Ill.u.s.tration: FIG. 112--A GAS FLAME IS SENSITIVE TO ELECTRIC WAVES]
If instead of a gas flame an incandescent-light bulb is used having a metal filament, and on either side of the filament a small strip of platinum, a more sensitive receiver is obtained. This is the audion, which is the distinguishing feature of the De Forest wireless telegraph and wireless telephone. The metal filament is made white hot by the current from a storage battery. The vacuum in the bulb is about the same as that of the ordinary incandescent electric light. A very small quant.i.ty of gas is therefore left in the bulb. The electrified particles of gas respond more freely to electric waves in this bulb than in the gas flame.
The De Forest wireless telephone was adopted for use in the United States Navy shortly before the cruise around the world in 1908. Every ship in the navy was equipped with the wireless telephone, enabling the Admiral to talk with the officers of any vessel up to a distance of thirty-five miles. The wireless telephone in use on a battle-ship is shown in Fig. 113.
[Ill.u.s.tration: FIG. 113--CAPTAIN INGERSOLL ON BOARD THE U. S.
BATTLE-SHIP "CONNECTICUT" USING THE WIRELESS TELEPHONE]
Wonders of the Alternating Current