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From the 1924 book, A Popular History of American Invention.
OUT of the horn or “loud-speaker” of the radio receiving apparatus wells the voice of a baritone, singing the prologue from “I Pagliacci.” It is as if he were in the room. How does his voice reach us? No wires connect the receiving instrument with the broadcasting station; it can not be a physical connection. The windows are closed; therefore, it cannot be the air. Besides, if it were the air, we would hear the voice in the street.
When we try to explain why we hear we are exactly in the position of scientists long before wireless communication was even a fantastic possibility. They were puzzled by light. What is light? Why does it reach us through the airless spaces that separate the earth from the blazing sun and the twinkling stars? Why does it pass through glass in which there is no air?
At first, it was thought that light possibly consisted of minute particles shot forth by burning candles or glowing stars. Among those who held this view was Sir Isaac Newton. Because the theory could not account for the colors in the rainbow or the tints reflected from mother-of-pearl and the crystals of chandeliers, it was dismissed.
Early in the nineteenth century, it was decided that light must be a wave motion in something. But in what? The scientists had to imagine a medium through which light travelled in waves, just as waves travel in water. This medium, which they called the “ether,” is supposed to pervade all space. Everything is plunged in the ether, including the atoms of which air is composed.
Rock a boat from side to side, and waves are set up in water. Atoms must rock to set up in the ether the waves that we call light. We can rock a boat a few times a minute and set up waves in water, but an atom must rock many millions of times a second in order to generate ether waves that we call light.
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|Wavelength and amplitude of a wave.|
When light was thus explained, it became easy also to explain its many hues. Color is to light what pitch is to sound—a matter of frequency of vibration. Violet corresponds to the highest pitch we can hear; the deepest visible red to the lowest audible pitch; and pitch, in turn, is dependent on the number of times something vibrates or rocks in a second.
All this and much more was known about light when Michael Faraday (1791—1867), who, according to Du Bois Reymond, an eminent German scientist, was “the greatest experimentalist of all times, and the greatest physical discoverer that ever lived,” began to study an electrical phenomenon which he called “induction,” and found out much about it that we now apply in radio communication.
In the whole history of science and invention, no more appealing example of devotion to truth-seeking, of self-denial, energy, and resourcefulness is to be found. Other great scientists had the advantage of a solid education. Faraday had no education whatever, in the collegiate sense. He even had to teach himself how to read and write.
When, as a bookbinder’s apprentice, he did learn to read, instinctively he turned to works on chemistry and electricity; which books prompted him to action. He repeated the experiments described in the books, going so far as to make himself an electrical machine with a glass bottle as a foundation.
And all this before he was fourteen. His copious, boyish notes of lectures that he attended are still preserved in the library of the Royal Institution: mute testimony of a dauntless spirit struggling against the enormous odds of poverty and lack of education to acquaint itself with the science of the day.
Such was Faraday’s thirst for knowledge that he was willing to forego all hope of gain. He wrote to Sir Humphry Davy asking for a post of some kind in the Royal Society. “What can I do?” said Davy, when he read his letter. “Do ?“ queried the man to whom he addressed himself. “Do? Put him to washing bottles.”
But Davy did more than that. Faraday was engaged at the pittance of twenty-five shillings a week to “attend and assist the lecturers and professors for and during the lectures,” and to make himself generally useful. His rise from a laboratory nonentity to the foremost scientific figure of his time was rapid.
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The part that Faraday played in the discovery of electrical principles is dwelt upon in the chapter on electricity. In that chapter Oersted’s discovery is mentioned—the discovery that an electric current in a moving wire can affect a magnetic needle.
Faraday began to think of the experiment. It proved that there is some relation between electricity and magnetism. If an electric current could influence a magnet, could a magnet, conversely, generate a current in a dead wire? Faraday thought so.
It took him seven years to obtain the evidence that he sought. One day he thrust a bar magnet into a coil of wire with which an electrical indicator (a galvanometer) was connected. The needle of the instrument swung in one direction when the magnet was inserted, and in the other when it was removed.
A current had clearly been “induced” in the dead coil, as the instrument proved. He found, too, that a moving electrified wire could similarly “induce” a current in a dead wire with which it was not in contact.
How was this phenomenon to be explained? This seemed to be a case of “action at a distance.” Yet the effect of the bar or of the current in the live wire had to be transmitted by something. “Action at a distance” was a phrase that explained nothing.
Faraday showed that the action, whatever it was, always occurred along definite lines, but the “something” by which the action was transmitted through space he could not divine.
MAXWELL BEGINS HIS STUDY OF ELECTRIC WAVES IN SPACE
It remained for another great Englishman, James Clerk Maxwell, to reveal the true nature of the “something,” the medium that transmitted electrical effects through space. Maxwell was primarily a mathematician He reasoned rigorously on paper with symbols and formulas.
Unlike Faraday, he was a graduate of a university, in fact, of two universities: Edinburgh and Cambridge. Maxwell was a born mathematician, and at fifteen he was making contributions to higher mathematics. He thought mathematics by day, and dreamed mathematics by night. Doctor Garnett, his biographer, thus describes his curious habits at one time of his life:
“From 2 to 2.30 A. M. he took exercise by running along the upper corridor down the stairs, along the lower corridor, then up the stairs, and so on until the inhabitants of the rooms along his track got up and laid perdus behind their sporting doors, to have shots at him with boots, hair-brushes, etc., as he passed.”
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|JAMES CLERK MAXWELL. Maxwell was an English physicist who first mathematically demonstrated the possible existence of the waves now used in radio communication.|
So attracted was this profound mathematician by Faraday’s work, that an article of his contributed to the ninth edition of the Encyclopedia Britannica remains to this day one of the most eloquent and just appraisals of Faraday’s position as an experimental scientist.
It was the mathematical explanation of Faraday’s discovery of induction, the revelation of what the mysterious “something” is that transmits electrical effects at a distance, with which Maxwell’s name is immortally linked. He read Faraday’s description of the induction experiments with something like deep, religious reverence. He saw how little the great experimentalist relished the idea of “action at a distance.”
Maxwell thought that electricity might possibly be transmitted by that same ether which scientists had created in their minds to explain the transmission of light. He undertook a profound mathematical study of the way in which light flashes through space.
He was irresistibly forced to the conclusion that light waves are electromagnetic waves. But Faraday was also dealing with electromagnetic waves.
Might there not be electromagnetic waves that could be seen, what was called “light,” and also electromagnetic waves that could not be seen? Was that the explanation? And was the “something” that transmitted Faraday’s effect through space, nothing but the old, familiar ether?
The questions almost answered themselves. Maxwell boldly announced that Faraday’s “something” that “induced” electrical effects at a distance was nothing but the ether. It was known that light travelled at the stupendous rate of 186,000 miles a second.
Maxwell predicted that if the electrical wave motion with which Faraday experimented could be measured, it, too, would be found to travel at the speed of 186,000 miles a second. He even went so far as to maintain that the electric waves could be reflected and refracted like light.
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Maxwell developed this view in a classic book of his called Electricity and Magnetism, which appeared in 1873. Such was his reputation in Europe as a leading mathematician of his time, such was the convincing nature of his mathematical proof, that his theory was accepted.
And yet, it was only a theory. No one realized this better than Maxwell, but so sure was he of his conclusions that he looked forward with confidence to the experimental proof of his views. He did not live to see them triumphantly vindicated; for he died in 1879 when only forty-eight.
Why can we see the electromagnetic waves that we call light but not the electromagnetic waves with which Faraday experimented in his induction researches.
For the same reason that we can hear only a few notes. If a sound consists of less than sixteen vibrations a second, we hear merely its separate thuds; if it consists of 10,000 vibrations a second we hear it as a very shrill, high-pitched note; if it consists of more than 32,000 vibrations a second we cannot hear it at all.
Something must rock or vibrate at least 400 million-million times a second in order that we may see what we call light. But the waves about which Maxwell reasoned mathematically are produced when something rocks or vibrates 10,000 to 3,000,000 times a second.
In other words, some electromagnetic waves could not be seen because they were generated at frequencies so low that the eye could not respond to them. Stated, in another way, Maxwell’s waves cannot be seen because they are too long; for the length of a single wave may be anything between a few inches and a score of miles.
On the other hand, the waves of visible light are so short that from 30,000 to 60,000 of them are compassed within an inch.
HERTZ INVENTS AN “EYE” TO SEE THE INVISIBLE WAVES
What was needed, then, was not only a way of generating these invisible waves, but a kind of artificial eye which would see them. After Maxwell had published his startling theory, scientists in several countries tried hard to render them visible.
The successful man was Heinrich Hertz, a modest German professor at the university of Bonn, who freely acknowledged his debt to Maxwell, and who was so self-effacing that he went so far as to declare that had he not experimentally confirmed Maxwell’s conclusions, another Englishman, Sir Oliver Lodge, would surely have done so.
|HEINRICH HERTZ. Hertz was a German professor who experimentally verified Maxwell’s prediction of the existence of invisible electromagnetic waves in the ether of space—the waves now used in radio communication.|
Hertz’ experiment is so simple that it seems astonishing that it was not made before his time (1887). He created electric sparks, little flashes of artificial lightning in his laboratory. At the opposite end of the laboratory he mounted what he called a “resonator”: a metal ring not completely closed, and therefore provided with a little gap.
When sparks crackled in the sending apparatus, tiny answering sparks crackled in the gap of the ring. This in itself did not prove that light and electromagnetic waves are one and the same, as Maxwell maintained. But Hertz proved that the waves were reflected from suitable surfaces just as light is reflected from a mirror.
The whole scientific world was aroused by Hertz’ confirmation of Maxwell’s theory. In France, in England, in Russia scientists began to study these newly discovered waves, which, fittingly enough, were christened “Hertzian waves.”
To detect them, artificial eyes were invented, far more delicate than Hertz’ simple open metal ring or resonator. Popoff, the Russian, at once began to study lightning; for lightning is a gigantic spark which also sends waves that can be detected. Lodge, in England, and Branly, in France, performed notable experiments, all of which did much to add to our knowledge of the waves.
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|DOCTOR EDOUARD BRANLY. Long before the days of the crystal and vacuum-tube detector Branly invented a detecting device known as the “coherer.” This device was simply a glass tube filled with metal filings, which cohered when the current from the receiving antenna passed through them, and therefore became conducting, and which were “decohered” by tapping them. Marconi used such coherers in his early receivers.|
And yet, not one of these distinguished scientists realized that waves in the ether might be used to send intelligible messages over a great distance. Perhaps they were too engrossed in the purely scientific aspects of their work to bother about the practical application of theories; perhaps it was because the distance over which they could transmit waves—a few hundred feet—did not fire the imagination.
Long after radio communication was an established fact, Lodge wrote frankly that, so far as he was concerned, he “did not realize that there would be a practical advantage in . . . telegraphing across Space. . . In this non-perception of the practical uses of wireless telegraphy, I undoubtedly erred.”
It was Sir William Crookes who first saw that the waves about which Faraday and Maxwell had theorized, and the existence of which had been proved by Hertz, might be practically applied in signalling through space. In a memorable article published in the Fortnightly Review in 1892, on “Some Possibilities in Electricity,” he wrote:
“Here is unfolded to us a new and astonishing world—one which it is hard to conceive should contain no possibilities of transmitting and receiving intelligence. Rays of light will not pierce through a wall, nor, as we know only too well, through a London fog.
“But the electrical vibrations of a yard or more . . . . will easily pierce such mediums, which to them will be transparent. Here, then, is revealed the bewildering possibility of telegraphy without wires, posts, cables, or any of our present appliances. . . .
“What, therefore, remains to be discovered is—firstly, a simpler and more certain means of generating electrical rays of any desired wave-length, from the shortest, say of a few feet in length, which will easily pass through buildings and fogs, to those long waves whose lengths are measured by tens, hundreds, and thousands of miles;
“secondly, more delicate receivers which will respond to wave-lengths between certain defined limits and be silent to all others;
“thirdly, means of darting the sheaf of rays in any desired direction, whether by lenses or reflectors, by the help of which the sensitiveness of the receiver . . . would not need to be so delicate as when the rays to be picked up are simply radiating into space in all directions, and fading away. . . .
“Any two friends living within the radius of sensibility of their receiving instruments, having first decided on their special wave-length and attuned their respective receiving instruments to mutual receptivity, could thus communicate as long and as often as they pleased by timing the impulses to produce long and short intervals on the ordinary Morse code.”
It would be difficult to present a more accurate picture of radio communication both in principle, as well as in practice, than this.
MARCONI’S FIRST EXPERIMENTS
Such was the “state of the art,” as patent lawyers say, up to 1896. Electric waves had been sent out into the ether and “seen” by special “eyes” or detectors. Crookes foresaw the possibility of telegraphing through space, but no one had actually done so.
And then a mere boy began a series of experiments that culminated in a complete realization of Crookes’ prophecy. He was Guglielmo Marconi, the son of an Italian father and an Irish mother.
|GUGLIELMO MARCONI, INVENTOR OF WIRELESS COMMUNICATION. Courtesy Radio Corporation of America.|
In 1896, Marconi, then but twenty-two, received his first patent. In that historic document is disclosed what now seems an obvious invention. At the sending station was the familiar Morse key; at the receiving station the equally familiar receiving apparatus, in which a detector (Branly and Lodge’s form of “eye”) was included.
The Morse key was depressed. Sparks passed. They sent out waves into the ether. The key was released. The sparks and the waves ceased. Thus long or short trains of waves were sent out, corresponding with the dashes and dots of the Morse code.
The receiver responded sympathetically. The eye or detector “saw” while the key was down; it saw nothing when the key was up. It received invisible telegraphic flashes.
Marconi had improved on Hertz’ original sender so considerably that when he demonstrated his invention before the British post-office officials in 1897 on Salisbury Plain, he transmitted signals four miles.
And yet there was not a single original element in his apparatus. This is not said to his discredit. Morse’s telegraph, indeed every epoch-making invention, is usually a new combination of old elements, producing a new result.
That Marconi is a great inventor, that he has the imagination that always makes great inventors, is proved by the mere fact that, for all their great attainments, Hertz, Branly, Lodge, and Popoff never dreamed of signalling through space, although they were experimenting with the electromagnetic waves almost daily for long periods.
Marconi discovered that his range could be increased if he elevated the wire constituting part of the sending circuit and connected it with the ground. Thus elevated, the wire looked for all the world like the feeler of some gigantic insect, and hence it came to be called an “antenna.” Wires were similarly elevated at the receiving station with corresponding good effect.
In his early work Marconi even used kites to carry his wires far up into the ether. The great transoceanic stations of to-day have antenna that reach up several hundred feet; indeed, the towers on which they are carried may be as tall as office buildings.
By the end of 1897, Marconi was signalling nine and ten miles. “Half a mile was the wildest dream,” said Sir William Preece of the British post-office, in commenting upon the hopes of the more optimistic who believed in Marconi.
SIR OLIVER LODGE DISCOVERS THE PRINCIPLE OF TUNING
The sun sends out waves of what we call white light, which is, nevertheless, a mixture of all the colors in the rainbow.
Sunlight is the equivalent of a noise. A red light is the equivalent of a single musical note because it consists of vibrations of one period only.
Marconi’s sparks were like flaming candles or matches compared with the sun—much the same in color but less dazzling. They were little noises.
It occurred to Sir Oliver Lodge in 1897 that a new principle might be introduced. Why not send out a beam of wireless waves which would be the equivalent of a musical note or of one color of light?
|SIR OLIVER LODGE. Lodge introduced the principle of tuning (syntonization) in radio communication.|
Hold a vibrating tuning-fork near a piano, and only that string of the piano which corresponds in pitch with the tuning-fork will vibrate in sympathy. Or, put on a pair of red spectacles and all the world seems red.
It is easy to see that Sir Oliver Lodge had the principle of tuning in mind. He wanted to send out waves of one electrical pitch only, and tune the receiving instrument so that it would respond to that pitch and to no other. This Lodge did by adjusting the sending and receiving apparatus to what is called the “wave-length.”
|THE SIMPLEST SOUND-WAVE. The photograph was made by Professor Dayton D. Miller, of the sound-wave produced by a tuning-fork in vibration.|
|THE WAVE PRODUCED BY A FRENCH HORN. The photograph was made by Professor Dayton D. Miller, of the Case School of Applied Science. It shows about the simplest type of wave produced by a musical instrument.|
|THE NOISE OF A BIG GUN. A noise-wave is erratic, as this photograph shows; a musical note is always of more or less regular wave conformation.|
We have only to recall the waves of the ocean to realize the possibilities. By “wave-length” is meant the distance from the crest of one wave to the crest of the next in the same train. The distance is large for big waves and small for little waves. The larger the waves or the greater the wave-length the more slowly do they travel.
This means that fewer of them strike the receiver per second, whether the receiver be an eye, an ear, a beach, or a wireless detector. If they are few we have a deep electrical note; if they are many, we have a high electrical note.
Lodge converted the wireless transmitting station into something like a tuning-fork that sends out waves of one note only. The receiving station could be attuned to that note and could thus exclude the signals that came from stations that were not using it.
This marked an enormous advance in wireless communication. A station could send one wave-length or electrical note to another station. The receiving station, knowing on what wave-length the transmitting station was sending, could “tune in” or vibrate in electrical sympathy.
The wave-length in radio communication may be anything from 1 to 50,000 metres. In radio communication, wave-lengths are always stated in metres. Translate these wave-lengths into ordinary language and compare them with other waves and their extraordinary character becomes immediately apparent.
The waves of the ocean may measure a few inches or several hundred feet. But the waves which are sent billowing through the ether by a transatlantic radio station may measure from four to twenty miles from crest to crest.
For short distance transmission the length of the wave may measure a few inches up to several hundred feet. Since he was dealing with waves that varied so widely in length, Lodge had devised a method of sending and receiving which had enormous possibilities.
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|INTERIOR OF THE LAFAYETTE STATION, FRANCE. The size of the wire is an indication of the amount of power that is radiated. To the right is a high-power tuning-coil.|
Marconi soon made arrangements with Lodge to apply this method of tuning to wireless telegraphing, with the result that he vastly increased the effectiveness of his system of communication. By this time, the Wireless Telegraph and Signal Company had been organized in England to buy Marconi’s rights. The Italian navy adopted wireless telegraphy.
By 1898 Marconi had established wireless communication across the English Channel, and had also reported the International Yacht Races between Sandy Hook and the office of the New York Herald; both considered marvellous exploits at the time.
The principal steamship companies equipped their vessels with Marconi wireless sets, and many a ship in dire distress was saved by their means.
Greater and greater distances were covered. In 1900 Marconi made a great advance. He devised a way of sending out powerful prolonged trains of waves. He tuned his receiver to the transmitter so that the detector was not easily affected by a single wave, as heretofore, but only by a train of waves of suitable frequency, thus extending Lodge’s principle.
After having succeeded in telegraphing with this system a distance of 200 miles, he decided to bridge the Atlantic. But he needed more power. His chief engineer, Professor J. A. Fleming, designed the stations.
A less courageous spirit than Marconi’s would have been daunted by the accidents that occurred in erecting tall aerials. Towers and masts were blown down by storms. It seemed almost hopeless for a time to triumph over nature.
Finally, with the aid of kites flown at Newfoundland, Marconi, on December 21, 1901, received from Poldhu, Cornwall, the three dots representing the letter “s.”
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|Marconi transmitting station in Poldhu, England.|
Refinements were now rapidly introduced to make transatlantic communication more efficient. Marconi invented a magnetic detector, which made it possible to hear the dots and dashes as musical notes of shorter or longer duration, and at once the speed of reception was increased to 150 letters a minute. Gigantic waves were shot out into space; waves measuring four to ten miles from crest to crest.
PROFESSOR FLEMING INVENTS THE OSCILLATING VALVE
The sparks or miniature artificial lightning flashes that Marconi used, sent out waves that produced currents in the receiving antenna. The current oscillations ran up and down the wire at the rate of half a million to a million a second.
The ordinary telephone, connected with the antenna, cannot respond to such rapid vibrations; hardly has the diaphragm begun to move when it is struck by another impulse.
It occurred to Professor Fleming that something like a one way valve was needed, something that would let current pass in one direction but not in the other. Thus every other oscillation that ran up and down the antenna would be suppressed, and the telephone would become more responsive.
|JOSEPH A. FLEMING. Fleming, an English engineer and physicist, who first applied the “Edison effect” in receiving wireless-telegraph signals. Courtesy Marconi Company (London).|
In the early eighties Fleming held the post of scientific adviser to the Edison Electric Light Company, organized to develop and introduce Edison’s system of incandescent lighting in England. Naturally, he was thoroughly acquainted with Edison’s researches.
Fleming recalled some experiments which Edison had made in 1883 and which had given the world what was known as the “Edison effect.”
For some reason, Edison had sealed within one of his incandescent-lamp bulbs a little plate of metal. There was no contact between the metal and the filament of the lamp; yet, when the filament glowed, a current would stream over from it to the plate, but only when the plate was positively charged.
This was the “Edison effect.”
The discovery lay dormant twenty-one years, unapplied. It flashed upon Fleming that this device of Edison’s constituted the very valve that he wanted. “Suppose,” he reasoned, “I use this lamp in my receiving circuit.
Positive and negative currents rush up and down the antenna. When a positive impulse passes through the metal, current will stream over from the filament; but when the negative impulse immediately following strikes the metal, nothing will stream over.”
He made the experiment. It proved brilliantly successful. Thus, in 1904, the Fleming “oscillation valve,” as it has ever since been known, was introduced in radio communication. It was the first of the modern radio vacuum-tubes. By its means, trains of very rapid oscillations were converted into spurts of electricity, all travelling in the same direction. The result was that the reception of telegraph signals was enormously improved.
In 1906, General H. H. C. Dunwoody, of the United States Army, discovered that certain crystals (carborundum, for example), also had the property of suppressing one-half the waves that rush up and down the antenna. Because such crystals are cheap, because there is no necessity for lighting a lamp, they are widely used to this day.
The cheaper radio telephone-receivers in these days of radiated music and lectures are fitted with such crystals.
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|LITTLE AND BIG VACUUM-TUBES. In one hand Doctor Langmuir is holding a small vacuum-tube of the type used in many radio sets for receiving broadcast speech and music; in the other he is holding a large twenty kilowatt vacuum-tube used for generating waves in the ether of space. Courtesy General Electric Company.|
|FIVE-WATT TRANSMITTING-TUBE COMPLETE AND DISMEMBERED. Courtesy General Electric Company.|
|VACUUM-TUBES IN A MODERN RADIO TRANSMITTING STATION. Courtesy Marconi Company (London)|
DE FOREST’s REMARKABLE DISCOVERY
Remarkable as was Fleming’s invention of the oscillation valve, still more remarkable was the improvement made by Lee De Forest, an American radio engineer. About 1906 De Forest inserted a tiny metal grid between the glowing filament of the lamp, or tube, and the metal plate.
When the grid was negatively electrified, current would not stream over from the filament through the meshes and on to the plate; but when the grid was positively electrified, the current rushed through the meshes and the plate was charged. The introduction of a grid between the filament and the metal plate does not seem much of an improvement; yet De Forest’s invention is as great as that of radio communication itself.
De Forest had only to include his little grid in the receiving circuit. As it was now positively and now negatively electrified, it assisted or arrested the stream that tried to flow from the filament. He had only to connect his metal plate with a telephone-receiver to hear the signals with wonderful clearness.
The little grid acted much like the throttle of a locomotive: it set powerful local currents in action, just as a locomotive throttle has only to be moved one way or the other to start or stop a freight-train.
What is more, these currents in the receiving circuit were simply a magnification of those that ran up and down the antenna.
De Forest could add another lamp or tube to the first and obtain still louder effects. Thus, by adding tube to tube he could magnify a signal millions of times. It is easy to see what this meant in radio communication.
Signals too feeble even for detection by Fleming’s valve could be clearly heard by a De Forest tube or two; the receiving range was increased several times. All the great feats of long-distance radio communication, feats that involve telegraphing half-way around the world, have been performed with this marvellous device, “the master weapon of the radio engineer,” as it has been called.
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|LEE DE FOREST. De Forest invented the modern vacuum-tube, one of the most remarkable inventions ever made in electricity.|
De Forest’s invention was at once applied in long-distance wire telephoning. Here was a device which made it possible to amplify feeble voice-currents just when they were beginning to vanish altogether. By inserting De Forest’s tubes at intervals in the line it became possible to telephone from New York to San Francisco.
It was thus that the electric current that carried President Harding’s oration on the occasion of the interment of our Unknown Soldier in Arlington, Virginia, was multiplied 3,000,000,000,000,000,000,000,000,000 times. Amplified 10,000,000,000 times the President’s words were heard by thousands in Madison Square Garden, New York. Higher amplifications were necessary in order that they might be heard in other cities.
A De Forest tube can magnify the ticking of a watch until it sounds like a trip-hammer. Moreover, the tube makes it possible to transmit over a single telephone wire half a dozen different conversations without interference, each conversation being transmitted in waves of a definite frequency.
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|HOW PRESIDENT HARDING TALKED TO THE NATION. When our Unknown Soldier was buried, President Harding addressed a vast audience in the Arlington Memorial, near Washington. But far vaster was the audience than that gathered before him. New York and San Francisco heard him, too—thousands who were hundreds and hundreds of miles away. This marvellous performance was made possible by using the vacuum-tube as an amplifier and as a relay. The voice of the President was carried by telephone to New York, where it was heard by a throng that filled Madison Square Garden, and from New York was repeated, as shown on this diagram, in cities between the Atlantic and Pacific Oceans. Courtesy Western Electric Company.|
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|LOUD-SPEAKER FOR LARGE AUDIENCES. In order that the speech of an orator may be heard in Chicago or New York by thousands, amplifiers of this type are mounted in auditoriums. The speech may be transmitted either over ordinary telephone-lines or by radio. The words of the distant orator are distinctly heard within a distance of one mile from this amplifier.|
ARMSTRONG AND HIS “FEED-BACK”
It was the World War that brought about the rapid development of the airplane, and it also made the radio-receiving set a household rival of the phonograph as a means of entertainment. War, wherein the lives of thousands of men are guarded, or imperilled, by superior scientific innovations, has always stimulated invention.
A case in point was Edwin Armstrong, a young American, who held a major’s commission. Even as a boy he had been interested in wireless telegraphy. Indeed, he was one of several hundred thousand American boys who built their own wireless sets, formed wireless clubs, and communicated with one another.
When he was old enough to enter Columbia University he took the course in electrical engineering. There he came under the influence of Professor Michael Pupin, a man who has done as much as any other in America to shape the course of modern telephoning and radio communication.
In 1912, while still a student, scarcely twenty-one years of age, Armstrong conceived the idea of making the vacuum-tube of De Forest even more effective than it was. We must remember that in the tube, a current streams from a glowing filament through a grid to a metal plate, and that in the local circuit, of which the plate forms a part, magnified currents are obtained similar to those received by the antenna.
It occurred to Armstrong that he would take part of this current and “feed” it back, thus obtaining still stronger effects. If a machine-gun could take the bullets that it has fired and discharge them again, the process would be similar to that conceived by Armstrong. The invention was a wonderful success.
With the “feed-back” of Armstrong, amateurs easily received signals from Germany, Honolulu, Darien, Norway, and the Philippine Islands. Since he used but few expensive tubes, his invention made it possible to manufacture receiving-sets of extraordinary sensitivity at a cost undreamed of before the war.
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|Edwin Armstrong developed feedback theory which amplified signals.|
HOW RADIO TELEPHONY DEVELOPED
It was well-nigh impossible to telephone with the sparks that Marconi used. The waves they generated in the ether were not of the right kind. The first requirement for radio telephoning is a source of waves, constant in form; every wave must be like every other wave in length and height.
Variations in the amplitude of the waves will introduce disturbances that prevent the effective transmission of speech. To appreciate how important is constancy of wave form, we have only to consider an ordinary swinging pendulum.
Set the bob in motion. The bob swings from side to side, but each swing or beat is of less amplitude than the preceding beat. Finally, the pendulum or bob “dies down.”
So it is in radio when a spark is used. The electrical vibrations, or oscillations, “die down.” In a clock the pendulum is kept in motion by the energy of the wound spring; each beat is equal in amplitude to that of the preceding beat. These beats are continuous, or undamped, oscillations.
The same phenomenon is observed in sound. Pluck the string of a violin and a short sharp note is heard that lives and dies in an instant. Draw a bow across a string and a note is heard that persists as long as the bow is in action. The plucked string emits damped sound waves; the bowed string undamped, or continuous, waves.
Marconi’s damped waves, suitable enough for telegraphing, were useless for telephoning. This becomes even more evident when we consider the process that occurs when we telephone over a wire. As we say “Hello,” we mould the electric waves that travel constantly through the wire into a “hello” pattern.
At the receiving end a diaphragm is caused to vibrate by the waves, and because they have been moulded by the voice into a “hello” pattern we hear the word “hello.” The moulded wave corresponds with the sound-groove in a phonograph record. What we hear is not the actual voice but a reproduction in either case. So it is in radio telephoning. Substitute the ether for the wire and the rest of the process remains the same.
It can now be seen why it was difficult, if not impossible, to telephone through the ether with electric sparks. They were constantly dying down, and therefore could not be moulded by the voice. The diagram below shows the difference between damped and continuous waves in radio communication.
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|DAMPED AND CONTINUOUS RADIO WAVES. A spark sends out damped waves, which die down. What is needed for radio telephoning is a continuous wave which persists.|
Many devices were invented for the purpose of generating continuous or undamped waves by means of sparks, but in vain.
Reginald Fessenden, an ingenious American engineer, tried using dynamos somewhat like those to be seen in modern power-houses. Nearly all electrically illuminated houses are supplied with what is called “alternating current.” Water flows in a pipe in one direction, but an alternating-current dynamo generates current that travels through the wire in two directions, back and forth.
These alternations or oscillations of current are just what we need in order to set up waves in the ether. The ordinary alternating-current dynamo in the power-house is useless in radio communication. It produces electric oscillations or alternations that number about 120 a second, and rarely more than 500 a second.
To generate waves in the ether something must rock back and forth not less than 10,000 times a second, and even as often as 3,000,000 times a second, as we have seen.
The construction of a dynamo, generating a current which would swing back and forth in a wire with this increased rapidity, was an engineering feat that required designing ability of a high order.
Fessenden pointed the way. Others improved on his method. Among them was R. Goldschmidt, a distinguished German radio engineer, and Doctor E. Alexanderson, a Swedish engineer, who became a naturalized American.
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|THE ALEXANDERSON ALTERNATOR. This machine looks like an ordinary generator, such as may be found in every electric central station. It is not an ordinary generator, however, but an Alexanderson alternator, especially built to generate the high-frequency currents used in radio communication. These alternators have already given place to vacuum-tubes. Courtesy Radio Corporation of America.|
Their dynamos sent out waves that did not rapidly die away—continuous waves which could be moulded by the voice into a pattern that a telephone-receiver would reproduce. But the machines were difficult to design and expensive to build.
It occurred to the Danish engineer, Valdemar Poulsen, inspired by the suggestion of Duddell, an Englishman, that perhaps arcs might be substituted—arcs such as those that glow in many of our streets. Such an arc, he argued, was a permanent spark, not constantly formed and broken.
But ordinary street arcs could not be used. They would fail to generate oscillations of many thousands per second. In 1903, Poulsen devised a special arc that met the requirements, and when that was done radio telephoning became easy.
But although dynamos and arcs are used both in radio telegraphy and radio telephony, the vacuum-tube of De Forest has already taken their place; for the tube can be used not only to receive and amplify the feeble waves that come from some far-distant station, but also to generate continuous waves.
The time is rapidly approaching when dynamos, arcs, and sparks will all give place to tubes. Only continuous waves will be used, even for telegraphing over short distances. The same transmitting station will, therefore, serve both for telegraphing and telephoning, just as receiving instruments now reproduce the dots and dashes of the Morse code and the human voice.
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|ARC OF THE BORDEAUX STATION. Within this casing is an arc which resembles the arc that glows over many a street corner. But this arc is very much larger and is prevented from breaking or being extinguished by a very complicated arrangement of magnets. Arcs of this type were used for radio telephoning by the Danish engineer Valdemar Poulsen.|
As soon as a method of generating continuous waves, waves that would not die away, was discovered, it became easier to transmit speech through the ether. Since Reginald Fessenden was one of the earliest of these successful experimenters, it was but natural that he should have been the first to transmit speech by continuous waves.
As early as 1903 he had succeeded in telephoning a distance of about a mile. In 1906 he increased this distance to ten miles. From that year on, as the action of De Forest’s vacuum-tube was better understood, progress was rapid.
In 1915 a record was made. The human voice was transmitted from Arlington, near Washington, D. C., to Honolulu. And now we have radio broadcasting stations by which music, lectures, news, and stock-market reports are sent out for hundreds of thousands to hear.
In a sense, broadcasting has always been with us. Every radio station radiates its messages, whether they be telegraph signals or spoken words, into space. Any one who has the proper electromagnetic ear can hear them.
But not until 1920 was broadcasting placed upon a permanent commercial basis. It occurred to a few imaginative engineers of the Westinghouse Electric and Manufacturing Co., that interest in radio communication might become even greater than it was if songs and band music were broadcast.
The experiment was timidly made. “Did you hear us ?“ the announcer at the station asked. “Did you like it? Do you want more of it?” The response was overwhelming.
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In a few months factories were working night and day trying to meet the demand for home radio telephone-receiving sets. Broadcasting stations were established in nearly every large community, chiefly by newspapers, department stores, and radio manufacturers.
Some indication of the radio future thus ushered in is given by the feats of the present day. Already opera is broadcast. Zanzibar, Florida, Minneapolis, and St. Louis will all listen, some day, to Metropolitan Opera. The remotest ranch, the solitary ship at sea, will be present at the first performance of a Broadway theatrical performance; at least so far as the ears are concerned.
Fairy-tales for children? We have them now. The imagination conjures up a radio mother of the future, crooning bedtime songs and telling bedtime stories on a prescribed wave-length to 10,000,000 children who may live anywhere between Alaska and Florida.
Education by radio? Its present rudimentary beginnings will be totally eclipsed by lectures delivered to millions of students by the professors of some radio university located in London or New York. Symphony orchestras will play to whole continents, peninsulas, and islands.
Here is an invention that will cause space to shrivel up, that will convert a whole country, even half the planet, into a single huge auditorium. No prediction of radio’s future can be so wild, so fantastic, that even the most unimaginative engineer will dismiss it as impossible of realization.
Look at a map of the United States and try to conjure up a picture of what home radio will eventually mean. Here are hundreds of little towns set down in type so small that it can hardly be read. How unrelated they seem!
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|“RADIO CENTRAL” AS IT WILL APPEAR WHEN COMPLETED. Twelve lines of towers radiate from a central power-house, each line pointing to a particular part of the world. Thus waves can be sent out which are destined for any country in Europe, Asia, South America, Africa, or the Southern Pacific. The towers, each about as tall as an ordinary office building, carry the antenna. Courtesy Radio Corporation of America.|
|THE TOWERS OF “RADIO CENTRAL,” PORT JEFFERSON, LONG ISLAND. One of the twelve lines of steel towers on which the antenna of the great station of the Radio Corporation of America at Port Jefferson, Long Island, are carried. Each antenna consists of sixteen bronze cables, stretched horizontally from tower to tower. When the station is completed there will be 300 miles of cable. Each tower is 410 feet high, and the cross-arm or bridge which supports the antenna wires at the top is 150 feet long. Courtesy Radio Corporation of America.|
Then picture the tens of thousands of farmhouses on the prairies, in the valleys, along the rivers—houses that cannot be noted. It is only an idea that holds them together—the idea that they form part of the United States.
One of them might as well be in China and another in Labrador were it not for this binding sense of a common nationality. All these disconnected communities and houses will be united through radio as they were never united by the telegraph and the telephone.
The President of the United States delivers important messages in every home, not in cold, impersonal type, but in living speech; he is transformed from what is almost a political abstraction, a personification of the republic’s dignity and power, into a kindly father, talking to his children.
The telegraph and the telephone have been called “space annihilators” in their day. Space annihilation indeed!
We never really knew what the term meant until the time came when thousands listened at the same time to the voice broadcast through the ether just as if they were all in the same room. Somehow the world seems to contract into a little ball on which Patagonians, Eskimos, Chinese. Americans, Kaffirs, and Apaches are next-door neighbors.
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