No one in the Arabian Nights understood the Lamp. All that was known was that when one rubbed it an omnipotent genie appeared who would do whatever was commanded. Beyond this all was dark deep mystery.
The change that has come in our day is the discovery of the principle of the Lamp. Hitting upon the thing by lucky accident, our modern Aladdins were not content to let it work in secret. They had to explore; they wanted to see how it worked, why it worked, just how many slaves it controlled, and what jobs could best be entrusted to each slave. Out of these laboratory explorations have come new types of lamps, new refinements, greater power, more specialization, wider diversity — and miracles.
There is a lamp that can carry you, as on a magic carpet, far away. Recently I sat in a narrow room in downtown New York. A lamp glowed in front of me, and its flickering light arranged itself into the familiar pattern of a face. It was the face of a man I knew to be two miles away. Suddenly his image began to speak, ’I see you clearly. Can you see me?’ and I realized that I had been transported to his sight and hearing by the same magic of glowing lamps that had brought him to me.
This was only a two-mile wire communication of television, but day after to-morrow it may be a 2000-mile broadcast by wireless of a whole opera troupe and orchestra in performance. We know it can be done, because we know the principle of the lamp. The actual accomplishment is only a matter of development, and it may come gradually over a period of years or with a bewildering rush as radio broadcasting came less than a decade ago.
There are lamps that can carry your command around the world and put it into effect anywhere you will. Guglielmo Marconi sat in his yacht in the harbor of Genoa one day last March and touched a button. Instantly thousands of electrical slaves leaped into action in Sydney, Australia. It was a lamp on his yacht shaped to pulse in harmony with other lamps in Australia that made his will effective eleven thousand miles away.
The same sort of magic was worked in a New York office. A large steel mill in Pennsylvania had been electrified, and the company decided to signalize the turning on of power in a special way. When the day came, the electricians installed a glass bulb in the New York office. The head of the steel company sat at his desk, he brushed the bulb lightly with a wave of his hand, and in a flash electric power surged through the gigantic machines of the industrial plant five hundred miles away. No cavalry officer’s command ever brought so many thousands of horsepower into action.
There are lamps that can hear. One of these electric ears was demonstrated at the Newark Airport recently. It is so attuned that it will respond only to the peculiar note of a certain siren. An airplane came circling in out of the darkness, and sounded its call. The electric ear heard, instantly summonsed its slave, — that is, operated a switch which turned on the port’s floodlights, — and so the aviator was lighted home.
Other lamps can see and report what they see. Several of these electric eyes have been installed at entrances to the international bridge at Detroit. They count each vehicle as it passes and keep books on the day’s tolls; they report to the central office any congestion of traffic.
Similar eyes are on duty in the Holland Tunnel under the Hudson River between New York and Jersey City. When smoke reaches a certain density in the tunnel, the electric eye sees it, flashes a signal which closes a switch, and fans begin to draw out the bad air while other fans pump in fresh air.
The same kind of lamp is on guard in a New Jersey schoolroom. On cloudy days, when sunlight dims, the eye of the lamp sees and relays a signal which turns on the electric lights. The lamp is as keen to economize current as it is to safeguard eyesight, for when the clouds roll away and the sun floods the room again it quickly swings the switch and turns off the electrics.
Another type of lamp can look through a solid and reveal its contents. An airplane manufacturer is using this in inspecting wood to detect wormholes, knots, and cracks. At the Watertown Arsenal in Massachusetts the same device is inspecting steel for the big artillery. It can peer equally successfully through several inches of metal and reveal the inner flaw, or through an unopened oyster and spot the hidden pearl — so sensitive, so penetrating, so delicate, and at the same time so powerful are its rays.
All of these magic lamps are ‘merely’ vacuum tubes, of course — variations of the familiar radio tube, that strange new device of the laboratory which broadcasting has brought into our homes. Science is rapidly harnessing it to a diversity of uses. A recent tabulation in an engineering journal enumerates 178 existing applications of the vacuum tube to industry, art, surgery, medicine, navigation, aviation, railroading. And yet, say the experts, the present accomplishments of the tube are but a beginning of the uses to which it will be put as physicists and engineers penetrate more deeply into its principle and master its mechanics.
Commenting on the unusual versatility of the device, O. H. Caldwell, former Federal Radio Commissioner, recently appraised the invention of the vacuum tube as comparable in importance to Archimedes’ discovery of the power of the lever. ‘For the vacuum tube is, in effect, an electrical lever,’ said Mr. Caldwell. ‘And just as the principle of the lever is used again and again in every element of every machine built in this mechanical age, so the introduction of the vacuum tube and its associated circuits presents almost inconceivable possibilities in the electrical future. One may safely predict that, within a few years, there will be nothing that the average man sees, hears, or buys but will be controlled, regulated, or affected in some important respect by an electronic tube.’
Perhaps this is the lever that Archimedes was looking for when he boasted that, given a sufficient fulcrum, he could move the world.
Like many other important tools of civilization, the modern vacuum tube — or electronic tube, as engineers call it—is the product of many minds and of many experiments. But Thomas A. Edison glimpsed it first.
While working on his incandescent lamp in 1883, Edison noticed that when he heated the filament to a certain temperature a blue glow appeared between its legs. Was this electricity flowing through the rarefied air? If so, it seemed strange that the current should take this more resistant path in preference to the easier channel provided by the loop of the filament itself. To satisfy his curiosity the inventor inserted a second element into the bulb, a wire. He connected the wire to the positive terminal of the lamp and found that a weak current did flow from the hot filament. But, curiously, when the connection was changed to the negative terminal, no current flowed. Edison noted the experiment in his notebook and turned from this fascinating side issue back to his main job of developing the incandescent lamp.
He did not realize that he had stumbled on a principle that was to become the foundation of whole industries. He did not know that that altered electric lamp was to become historic as the first vacuum tube, the unsuspected granddaddy of the countless radio tubes now in use. But science remembers, and in the annals of physical discovery the phenomenon of electrical emission in a vacuum is known as the ’Edison Effect.’ A recent commentator calls Edison’s achievement here ‘the most epochal in all his eventful career.’
Many years passed before the Edison Effect was understood. Indeed, the professors had to develop a new physics before the curious glow could be explained in terms of what it is now known to be: namely, the result of a boiling off of electrons, or particles of negative electricity, from the hot filament and their flight through space to the positive wire. It was not until 1905 that this flow of power in a vacuum was harnessed to do useful work. In that year J. A. Fleming thought to try the tube as a detector of radio signals.
Radio, at this time, was in swaddling clothes. Marconi had succeeded in signaling across the Atlantic; he had established wireless telegraph stations at points along the British coast, at Cape Cod in the United States, and at Cape Breton in Nova Scotia; but he was handicapped by the limitations of his apparatus. His first detector had been a thimbleful of steel filings in a glass tube — a ‘coherer’ the device was called. Under favorable conditions it would respond to the dots and dashes of the Morse code. But now radio was reaching out for greater distance, aspiring to a reputation for dependable service; inventors were trying to substitute for telegraph the more delicate and elastic telephone communication, and a sensitive detector was an absolute necessity.
Radio waves are energy swinging first in one direction and then in the opposite, and the frequency of reversal may run up to millions of times each second. When these oscillations from a distant wireless station surged through space, they caused the filings in Marconi’s coherer to cling together. The electrified particles became a conductor through which the current alternated until a ‘decoherer’ tapped the glass tube and shook the filings apart, whereupon they ceased to conduct.
Wireless telephony needed something far more sensitive than this halfmechanical device. In particular it needed a detector that had the ability to ’rectify’ the incoming oscillations — that is, to eliminate the reverse flow from the alternating current and give the effect of a flow in one direction only. Without this rectification, wireless telephony seemed impracticable. Inventors tackled the problem, improved types of detectors were brought forward, but the need was not met.
At this stage it occurred to Professor Fleming, in England, that the Edison Effect possessed a significant peculiarity. You recall that in Mr. Edison’s experimental tube the flow of electricity occurred only when the wire was positively charged; when it was negative, current ceased. This suggested to Professor Fleming that the vacuum tube might serve as the needed radio valve. Millions of reversals might occur every second, but so long as the wire of the tube was kept positive it would attract only the negative side of each oscillation. The positive half would be shut off, and thus the effect would be that of a pulsating current in one direction. He rigged up a vacuum tube to test the idea.
It is not on record that Professor Fleming ran through the streets of London shouting ‘Eureka!’ but he might very well have done so, and been justified in his enthusiasm, for he had indeed ‘found IT.’ Radio had a second birth that day in 1905. Edison’s electron tube was rediscovered, recognized as something more than a scientific curiosity — though no one dreamed a fraction of the talents that were hid in its vacuum.
Like Saul in the Old Testament story, who went out to seek his father’s asses and found a kingdom, the pioneering professor had grasped something so fundamental and so universal in its scope that it may well be said to include the whole kingdom of radio. For the vacuum tube has turned out to be not only the most sensitive detector, but an all-powerful amplifier, a relay, and a generator. It can rectify an alternating current, or, vice versa, convert a direct current into an alternating one.
These varied gifts were not discovered all at once. Honors must be divided among many experimenters. Fleming improved on Edison by enlarging the wire into a metal plate. Lee DeForest, a doctor of philosophy just out of Yale, improved on Fleming by adding a third element, a metal mesh which he placed between the filament and plate; because its appearance suggested a diminutive gridiron he called it the ‘grid.’ This grid provided a fulcrum for the electrical lever, increasing enormously both its sensitivity and its power. Next, Irving Langmuir, a college professor who had abandoned teaching to pursue research in a Schenectady laboratory, and H. D. Arnold, a telephone engineer in New York, each began to experiment in his own way with vacuum pumps to see what would happen in tubes evacuated down to the last removable molecule. Before this it was believed that a little air aided the proper functioning of vacuum tubes; but these scientists, working independently, proved that the higher the vacuum the more steady the performance of the tube and the greater its capacity. Then E. H. Armstrong, a young physicist just out of Columbia University, invented a circuit known as the ‘feed-back’ by means of which a vacuum tube could be made to oscillate and so generate radio waves. It turned out later that both Langmuir and DeForest were working successfully on this same problem. Out of these varied experiments the vacuum tube won a place in the transmitting station, and so began its present reign at both ends of the radio world.
All these inventions had been made by 1917, but the tubes were small, their power limited to fractions of watts where to-day we have kilowatts. There were no broadcasting stations; radio was still very much a thing of the Morse code, a means of communicating between ships and shore, a war-time emergency service. The ordinary citizen was sometimes startled into ‘ohs’ and ‘ahs’ by the occasional newspaper stories of radio stunts, but when he had a message to send he usually dispatched it by wire or by cable. To-day — with a hundred million vacuum tubes at home in the cottages and palaces of North America, and with the demand for more so great that one manufacturer has a daily capacity for 270,000 tubes — how far off and antique and quiet seems that pre-radio age!
Meanwhile, though the public did not know it, the vacuum tube was beginning to edge into the home. It came in through the telephone wire — for telephone engineers were first to see that the lamp which Dr. DeForest had developed for radio could serve other causes too.
These engineers had been struggling for years to devise a means of telephoning across the American continent. Before 1914 the practical limit of conversation was the distance between New York and Chicago, though New York had reached Denver experimentally by using copper conductors nearly as big as trolley wires. The prospect of further enlarging the wire and of imposing more powerful currents seemed doubtful; for an electrical impulse weakens at an increasing rate as it travels over a wire, and large initial energy was necessary to send it even a few hundred miles. To talk over a direct wire of the usual size the 3400 miles from San Francisco to New York would require power in San Francisco equal to the combined output of all the power plants of the world — hundreds of millions of horsepower.
Long-distance communication was made possible by means of repeaters, electromagnetic devices stationed at intervals along the line to pick up the weak impulses and send them forward renewed and strengthened. With these aids the service between New York and Chicago had been put on a commercial basis, but to send the current through to San Francisco more powerful repeaters were needed. The telephone management was eager to get this transcontinental service into operation by 1915, and the Panama Pacific Exposition of that year would provide an occasion to emphasize the new service.
At this stage, along came the vacuum tube with its growing radio reputation. Why could n’t it be made to perform the desired service for telephone waves, since it was doing so well by radio waves? Dr. Arnold and his colleagues developed it and adapted it as a repeater. It was tried out, and it performed beautifully. The American Telephone and Telegraph Company paid Dr. DeForest $250,000 for certain patent rights in his three-element vacuum tube; the new device became a standard part of telephone equipment. When the 1915 exposition opened, New York and San Francisco were on easy speaking terms, and to-day it is possible to talk to any place to which wires can be stretched.
The modern telephone would be crippled if suddenly deprived of its vacuum tubes. They have become vital, not only in bridging distance, but in a score of ways of getting more work out of the line. Through their use, for example, it is possible to send on a single pair of wires four simultaneous telephone messages and twenty simultaneous telegraph messages.
Such capabilities could not be hid. Other industries needed electrical amplifiers. The phonograph had long been handicapped by the limitations of its mechanical methods of making records. There were those who dreamed of substituting electricity for mechanics, but they were thwarted by the lack of an amplifying device sufficiently sensitive to pick up the fragile impulses generated by sound waves and able to magnify them into currents strong enough to actuate the cutting needle of a wax recorder. Now, in the vacuum tube, they found a stepping-up device perfectly adapted to their requirements — and to-day all phonograph records are recorded through a microphone with the aid of Aladdin’s Lamps.
This power of the vacuum tube to magnify fragile waves without distortion has been harnessed to many uses. By means of it physicians are able to detect the slightest murmur of a beating heart, and to listen in on the lungs and other inward parts. Ship officers now take soundings by an echo process while the vessel steams onward, and sea-bottom surveys which formerly occupied months are now completed in a few days. Modern prospectors for minerals are probing into the earth’s crust electrically and feeling out the hidden ore — again through this amazing ability of the vacuum tube to make a mountain out of a molehill.
An amplifier is one thing; a relay is something different. It provides, not magnification of the original waves, but the control of power. A switch needs to be turned, a door opened to admit a larger flow of electricity, or closed to shut it off. Here, again, the vacuum tube has proved itself better than mechanical devices, and indeed has opened up possibilities for which there was no mechanical control sensitive enough, quick enough, or rugged enough.
For example: There is a certain industrial plant in uptown New York which is going day and night. Perhaps, as you pass, its continual hum challenges your curiosity, and you try to enter. The door is locked. Maybe you are persistent and unconventional, and try the window. Look out! There is an electrical watchman on guard. Your fumbling with the window has set up vibrations in his electric ear which are sufficient to trip an electric switch, and now an alarm is sounding at headquarters notifying the management of your threatened intrusion. And he will continue to tell on you till you let go the window and abandon your trespass.
There is no other attendant at this plant — an electric power substation — and apparently none is needed. If a fuse flashes, if flood rises, if anything out of routine happens, the electrical watchman hears it or sees it or feels it, and by his relay tubes reports it. Four hundred power stations in the United States are equipped with electrical watchmen whose quick-acting brain is a vacuum-tube relay.
Then, there is the electrical ‘Old Man Reliable’ which I have seen riding perched above the cowcatcher of a fast train in New England. His job is to feel out the condition of the track ahead and report continuously to the locomotive engineer — when to go full speed, when to go slow, when to stop. In an emergency Old Man Reliable, through his powerful vacuum-tube relay, throws on the brake and stops the train.
An electrical engineer recently faced the problem of providing an apparatus to open a high-voltage circuit 400 times a minute. No mechanical switch could endure the ordeal many minutes. But a vacuum tube was made which easily opened the circuit at the required speed, and used only a rivulet of electricity to control a flow millions of times greater. It was as though a fly were swinging the gate of a huge corral, alternately releasing and stopping hundreds of charging horses. Relay tubes have been made to operate in a ten-millionth of a second.
Then, there is that other talent of the vacuum tube — its ability to oscillate and generate waves of energy. This, of course, is the secret of the modem broadcasting station; but, like other gifts of the Lamp, it has been turned also to other purposes. Thus, in Carnegie Hall last April a New York audience was entertained for two hours with selections from Beethoven, Brahms, Wagner, Handel, and other music masters, played on tuneful vacuum tubes. The tubes were arranged in combinations of frequencies to embrace the musical scale and to simulate certain orchestral instruments. The musicians stood on the stage behind the cabinets in which the vacuum tubes vibrated, and controlled their volume and tempo by waves of the hand. A weird, unnatural, mechanized performance? But so seemed a talk over the telephone fifty years ago.
In the Westinghouse laboratory in East Pittsburgh I saw this oscillating power of the vacuum tube used to produce, not sound, but light. The light, like the concentrated beam from a powerful searchlight, was trained on the whirling propeller of an airplane, focused on one tip of it, and instantly it seemed that the propeller stood still.
I could see the very grain and texture of its wood, as though the thing were held there for inspection under that dazzling beam — and all the while the propeller was turning 1000 revolutions a minute. The illusion was produced by the frequency of the lamp, which was so controlled (through vacuum tubes) that it flashed for the tenmillionth part of a second at each revolution, timed and spaced to illuminate precisely the same spot at each flash. This device is being used to study the behavior of flywheels, turbines, gears, and other rotating parts while in motion.
Vacuum tubes are being used to generate high-frequency radiation to bake the tenacious moisture out of porcelain, to operate electric furnaces, and to stimulate in the human body artificial fever. The last-mentioned use of the tube has engaged the interest especially of Dr. Willis R. Whitney of Schenectady, and from the General Electric laboratory there he has supplied high-frequency lubes to the Albany Medical School, the Mayo Clinic, and other medical centres where their therapeutic value is being further explored.
Practically any grid-controlled vacuum tube can hear through its microphone, feel through its antenna, and talk through its speaker, but none of them can see. For vision an entirely different type of tube is needed — the photo-electric cell. Its governing principle is the sensitivity of certain metals to light — the fact that when illuminated they give off electrons. The resulting flow of current is in direct proportion to the intensity of the illumination, and because of this the electric eye can report with superhuman speed and accuracy anything it sees.
Thus, in a certain power house a photo-electric cell keeps watch over a giant dynamo. Again and again this electric eye has seen the beginning of a threatening flash-over and has switched off the power before the flash developed its destructiveness. In each case the whole episode was over before the human eye saw its beginning.
A tobacco company installed photoelectric cells to sort cigars by color. The human sorters had been able to distinguish six shades of brown, but the electric eye saw finer color distinctions and separated the cigars into ten grades. The same unerring sense of color has been called into service by peach canners. It seems that housewives who open two cans of peaches for Sunday night supper require all the fruit to be of uniform color.
A factory in Cincinnati employed inspectors to watch its packaged goods as they came from the wrapping machines. Defective packages got by the human eyes; but when a photo-electric cell was put on the job it caught every defect — and by operating a relay tube it promptly and unfailingly pushed off the traveling belt every unit that was lacking in wrapping or label.
Many industries are using the electric eye as a counter. It is obvious that if a beam of light is kept focused on a photo-electric cell, and an object passes between the light source and the cell, each interruption will be recorded. In a box factory an electric eye is counting paper by this means at the rate of three hundred sheets a minute. In a New York museum one guards the entrance, and not only counts each visitor but actuates a speaker which greets him with a ‘Come in’ and instructs him to sign the register. Quite in contrast with this gentlemanly task is the grueling job to which a photoelectric cell was assigned in a steel mill. It reverses the red-hot billets as they come from the rolls, and never misses or slips or shrinks from the heat.
Another use to which steel mills may apply the device is that of thermometer. It is said that the steel industry in America loses about two per cent of its production annually through inadequate heat control. If the metal is heated too high some of it burns; if too low, the result is brittle steel. Two per cent of the average production is about a million tons a year, and at fifty dollars a ton the waste becomes impressive. Photo-electric cells can measure temperature through variations in the light of the molten metal.
In Wilkinsburg, Pennsylvania, photo-electric cells are controlling traffic at a certain intersection of a side street with a main highway. In Elmira, New York, they are being tried as fire detectors to operate fire-extinguishing apparatus. S. M. Kintner, in a laboratory in East Pittsburgh, recently demonstrated the use of the electric eye as a burglar alarm.
The most extensive industrial application is in making and projecting sound pictures, the talkies which in more than 9500 theatres of the United States have supplanted the movies. It is the electric eye which makes television possible, and which enables the telephone and radio companies to send photographs with the same celerity and ease with which they send words.
The electric eye would be a puny thing, however, by itself. The currents which it sets up under the stimulus of light are feeble, and without vacuumtube amplifiers and vacuum-tube relays could do no useful work. Indeed, it is rare that a vacuum tube in any capacity will render the most satisfactory service as a solitary device; usually it needs the collaboration and reënforcement of other vacuum tubes. Lamps to generate energy, lamps to detect energy, lamps to magnify energy, lamps to call up new battalions of energy — each is shaped and tuned to do one job well, but in doing its specialty it generally needs the teamwork of other lamps.
Perhaps few readers think of the Xray lamp as a vacuum tube, but it is one of the most useful of the whole tribe. A few years ago it was confined to the laboratory and the hospital; but to-day the plumber may call in the X-ray to explore old walls for hidden pipes and forgotten wiring, and by means of it the art connoisseur verifies the genuineness of an old master. Manufacturers use it to inspect golf balls for symmetrical cores, to examine reclaimed rubber for nails and other foreign matter, to determine the adhesion of rubber to cords in automobile tires, to look through steel castings for inner flaws.
In the laboratory, the X-ray tube provides a new means of chemical analysis. Within recent years two new elements have been discovered with its aid. Geologists peer into fossils and botanists examine the inner structure of living plants by means of this same penetrating luminary which serves alike the artisan, the artist, or the researcher — whoever wishes to look into the inside of things.
The modern X-ray tube — which is really a generator of high-frequency oscillations of infinitesimally short waves — owes much to the research which developed other forms of vacuum tubes. Tungsten and molybdenum, those hard metals which were found so admirably adapted to the requirements of radio tubes, have been naturalized into the X-ray tube too. And with higher vacuua and with more controllable means of imposing high electrical pressures, X-ray tubes are made today which can send radiation through three inches of steel.
A whole flock of metals has come forward in importance with the rise of vacuum tubes. Tungsten and molybdenum were already in use in incandescent lamps; the demand for them is practically doubled by their use in vacuum tubes for filaments and other parts. Cæsium was little known in industry a few years ago; to-day, because its range of sensitivity to light closely approximates that of the human eye, cæsium is the metal most in demand for photo-electric cells, though potassium and rubidium serve as the light-sensitive metals in some tubes.
Other peculiar metals which the vacuum-tube development has brought into importance are the boosters. When a little is mixed into an alloy with tungsten to produce a filament, the activity of the filament is greatly increased. The presence of the booster speeds up the emission of electrons, and makes it possible to get more responsiveness from a tube with less power. One of these metals is thorium. Another is barium.
An engineer of the Bell Telephone Laboratories recently computed the economic value of barium, which is used as the booster material on the filaments of all vacuum-tube repeaters throughout the telephone system. The actual amount of barium on each filament is one twenty-fifth of a gram, — a microscopic pinch of metal, — but the computed saving which it brings to the system through its presence in hundreds of thousands of telephone vacuum tubes is $2,000,000 a year.
If the barium coating does that for a single industry, one wonders what must be the value of the vacuum tubes themselves to all industry — and to society. There is more to be considered, of course, than the dollars saved or the jobs lost. If the Lamps have brought noise and publicity and the waste of time into homes, if they have pushed art into mechanized moulds, and cheapened beauty in an attempt to broadcast that which cannot be broadcasted and to screen-picture that which cannot be filmed — let us remember that they have also brought rescuers to a sinking ship, placed new and more powerful aids in the hands of the physician and surgeon, and given the world an international voice which may yet prove the surest weapon in the peacemaker’s fight for a warless world. They have brought the electrical lever.