John Ambrose Fleming found an application for the Edison effect as a detector for radio waves, starting the electronics industry.

A number of events occurred in the twenty years before the invention of the vacuum tube by Sir John Ambrose Fleming that are relevant to its development. It is often the case that numerous events that contribute to a discovery are later overlooked or forgotten, and this is especially true with regard to the vacuum tube. Since the mid-1800’s, many scientists had been working with the properties of electricity in glass apparatuses with most of the air removed. Because the concept of the electron had not been formulated, and because the idea that electricity could consist of particles with one two-thousandth the mass of hydrogen was completely foreign, scientists had no obvious way of tying all their observations together and making predictions for systems not yet assembled. At that time, electricity was thought of only as a force and wave phenomenon and not as a particle. Vacuum tubes
Inventions;vacuum tube
[kw]Fleming Patents the First Vacuum Tube (Nov. 16, 1904)
[kw]First Vacuum Tube, Fleming Patents the (Nov. 16, 1904)
[kw]Vacuum Tube, Fleming Patents the First (Nov. 16, 1904)
Vacuum tubes
Inventions;vacuum tube
[g]England;Nov. 16, 1904: Fleming Patents the First Vacuum Tube[01100]
[c]Science and technology;Nov. 16, 1904: Fleming Patents the First Vacuum Tube[01100]
[c]Inventions;Nov. 16, 1904: Fleming Patents the First Vacuum Tube[01100]
Fleming, John Ambrose
Edison, Thomas Alva
De Forest, Lee

Among the earliest notable work leading to the discovery of the vacuum tube was that of Alexandre-Edmond Becquerel, Becquerel, Alexandre-Edmond who, as early as 1853, had worked out many of the conductivity properties of gases at various temperatures and pressures but could offer no explanation for these properties. Certainly the most important discovery leading to the invention of the vacuum tube was the Edison effect, Edison effect discovered by Thomas Alva Edison in 1884. While studying why the inner glass surface of a lightbulb (which, during this period, used a carbon thread for the filament) blackened, Edison inserted a metal plate near the filament of one of his lightbulbs. He discovered that electricity would flow from the positive side of the filament to the plate, but not from the negative side to the plate. Like other researchers, he made the observation but offered no explanation.

Edison had, in fact, invented the first vacuum tube, which was later termed the diode. However, as there was no use for the device at the time, the invention was not recognized for its true significance—it was a discovery much ahead of its time. A diode converts electricity that alternates in direction (alternating current) to electricity that flows in the same direction (direct current). Because Edison was a proponent of producing direct current in generators, he essentially ignored this aspect of his discovery. Like many other inventions and discoveries that are ahead of their time—such as the laser—the Edison effect was for several years “a solution in search of a problem.” The fact that the amount of electricity was proportional to the intensity of the filament, however, made it potentially useful as a control device for electric generators, and Edison was granted a patent on October, 1884, for this use of the Edison effect. He did not patent the use of his device as a diode.

The explanation for why this phenomenon occurred would not come until after Sir Joseph John Thomson’s discovery of the electron in 1897. In retrospect, the Edison effect can be identified as one of the first observations of thermionic emission—that is, the “boiling off” of electrons from hot surfaces. Electrons were attracted to the positive charges and collected on the positively charged plate, thus providing current, but they were repelled from the plate when it was made negative, and no current was produced. Because current flowed in only one direction, the effect was compared to a check valve used to allow a liquid to flow in only one direction. This analogy followed the popular practice of using the behavior of water as an analogy for electricity, and it is the reason the term “valves” became popular for vacuum tubes.

Another interesting invention related to the vacuum tube was developed by Arthur Wehnelt, Wehnelt, Arthur who was working with thermionic emission. On January 15, 1904, Wehnelt applied for a German patent on one of his tubes that converted alternating current into direct current. He did not mention its use at high frequency (that is, for radio waves), but only for low-frequency, power-generation applications such as charging storage batteries. He was the first to apply for a patent for a vacuum tube that had an application for the rectification of alternating current to direct current. Unfortunately, as Wehnelt did not mention the applicability of his device for detection of radio waves, he was unable to sell it for use in radio sets after Fleming applied for his patent, although it was quite suitable for application in radio sets.

Fleming, acting as adviser to the Edison Electric Light Company, had studied the lightbulb and the Edison effect starting in the early 1880’s, before the days of radio. Many years later, he came up with an application for the Edison effect as a radio detector when he was an electrical consultant for the Marconi Wireless Telegraph Company. Detectors (devices that conduct electricity in one direction but not another, just as diodes do, but at higher frequencies) were required to make the high-frequency radio waves audible by converting them from alternating current to direct current. Radio detectors Several types of detectors were available that relied on chemical reactions, physical actions, and properties of crystals, but they were not overly effective at high frequency.

Fleming was able to detect radio waves quite effectively by using the Edison effect. Ironically, he used a device that was essentially identical to the one that Edison patented, but for a different purpose and with a different external circuit: as a radio detector. Indeed, he even had the Edison & Swan Electric Light Company make up twelve units to his specifications for testing. Like Edison, Fleming offered no explanation of how or why his device functioned. Fleming’s device was also essentially identical to, although not as refined as, Wehnelt’s device, except that Wehnelt did not apply his invention to radio waves. Fleming applied for a patent on his device in England on November 16, 1904. He called his device the thermionic valve; Thermionic valves thermionic tubes are still called valves in England, whereas the American name is vacuum tube. The latter name reflects the fact that the device requires an internal vacuum in order to operate.

In 1906, Lee de Forest refined Fleming’s invention by adding a zigzag piece of wire between the metal plate and the filament of the vacuum tube. The wire was later replaced by a screen called a grid, which allowed a small voltage to control a larger voltage between the filament and plate. It was the first complete vacuum tube and the first device ever constructed that was capable of amplifying a signal—that is, of taking a small voltage signal and making it much larger. De Forest named it the “audion” Audions and was granted a U.S. patent on it in 1907. In 1907-1908, the ships of the U.S. naval fleet carried radios equipped with audions on their goodwill tour around the world. Although de Forest’s audion was useful as an amplifier of weak radio signals, it was not useful at that point for the more powerful signals of telephony. Other developments quickly followed as scientists realized the importance of the emerging fields of radio and telephony.

Although it took the world twenty years to understand the significance of the edison effect, it took only a short time after that to develop the electronics industry, Electronics industry which was especially pushed by the need for communications during World War I. With many industrial laboratories working on vacuum tubes, improvements came quickly. For example, tantalum and tungsten filaments quickly replaced the early carbon filaments. In 1904, Wehnelt discovered that if metals were coated with certain materials, such as metal oxides, they emitted far more electrons at a given temperature. These materials have a lower “work function”; that is, electrons escape the surfaces of the metal oxides more easily than they escape the surfaces of metals. An analogy is the greater ease of pumping water from a shallow well compared with a very deep well. Later work by Bell Telephone Laboratories Bell Telephone Laboratories showed that oxides of barium or strontium are particularly effective; all vacuum tubes soon used these coatings, which increased thermionic emission and, therefore, tube efficiencies by a factor of one hundred.

Another important improvement in the vacuum tube came with the work of Irving Langmuir Langmuir, Irving of the General Electric Research Laboratory starting in 1909 and Harold D. Arnold Arnold, Harold D. of Bell Telephone Laboratories. They used new techniques such as the mercury diffusion pump to achieve higher vacuums. Original tubes had about one ten-thousandth the pressure of atmosphere, whereas new techniques introduced after 1910 allowed vacuums below one-millionth atmospheric pressure. Working independently, Langmuir and Arnold discovered that very high vacuum used with higher voltages increased the power these tubes could handle from small fractions of a watt to hundreds of watts. The de Forest tube was now useful for the higher-power audio signals of telephone. This resulted in the first trans-American speech transmission in 1914, followed by the first transatlantic speech transmission in 1915.

In 1916, a long-standing conflict between the Marconi Wireless Telegraph Company, owner of the Fleming patent, and the de Forest Radio Company came to an end when a U.S. district court ruled that the de Forest audion, when used in any aspect of radio, violated the Fleming patent, although the audion could be used for telephony purposes. This gave Marconi a virtual monopoly in radio. In 1919, the domestically owned Radio Corporation of America Radio Corporation of America (RCA) was formed to buy out the foreign-owned Marconi Company because radio was so important to national security in the United States.

Over time, vacuum tubes became increasingly complicated, with additions of a second grid to produce the oscillation tube to accomplish the complicated purposes of future inventions. Vacuum tubes made the development of television, radar, radio, and numerous other inventions possible. From 1945 to 1950, vacuum tube sales in the United States exceeded two hundred million dollars each year.

The invention of the transistor Transistors in 1947 by William Shockley, Shockley, William Walter H. Brattain, Brattain, Walter H. and John Bardeen Bardeen, John ultimately led to the downfall of the tube. With the exception of cathode-ray tubes, such as those used in television picture tubes, transistors could accomplish the jobs of nearly all vacuum tubes much more efficiently. Also, the development of the integrated circuit allowed the creation of small, efficient, highly complex devices that would be impossible to duplicate with radio tubes. By 1977, the major producers of vacuum tubes had all ceased production. Vacuum tubes
Inventions;vacuum tube

• Bowen, Harold G. The Edison Effect. West Orange, N.J.: Thomas Alva Edison Foundation, 1951. A well-written, captivating account of the development of the vacuum tube. Accessible to the layperson.
• Fleming, John A. A Handbook for the Electrical Laboratory and Testing Room. 2 vols. London: “The Electrician” Printing and Publishing, 1901-1903. This laboratory manual is useful in that it illustrates the state of the art at the time the vacuum tube was invented. Although technical for its time, mostly in terms of equipment, it presents underlying theory that should be accessible for anyone who has had an introductory physics course.
• _______. The Thermionic Valve and Its Development in Radio-Telegraphy and Telephony. 2d ed. London: Wireless Press, 1924. The inventor of the first vacuum tube presents the history, development, and use of vacuum tubes in the early days. Some parts are very technical, others historical. Includes many figures and photographs.
• Hong, Sungook. Wireless: From Marconi’s Black-Box to the Audion. Cambridge, Mass.: MIT Press, 2001. Draws on archival evidence and recent work in the history of technology to provide a new perspective on the early days of wireless communication. Offers new insights into the relationship between Guglielmo Marconi and Fleming, who was his scientific adviser. Concludes with a discussion of de Forest’s audion and the shift from wireless telegraphy to radio.
• Stokes, John W. Seventy Years of Radio Tubes and Valves. Vestal, N.Y.: Vestal Press, 1982. A practical description of vacuum tubes from the earliest to those of the 1960’s. Identifies tubes by manufacturer, type, and physical description, and includes hundreds of photographs. Very useful for collectors.
• Tyne, Gerald F. J. Saga of the Vacuum Tube. Indianapolis: Howard W. Sams, 1977. Comprehensive volume on the development of the vacuum tube including relevant observations of the 1700’s, 1800’s, and early 1900’s about the properties of electricity, the development of vacuum technology, and other related studies. Includes illustrations of the first vacuum tubes and vacuum pumps as well as reproductions of pages from laboratory notebooks.

First Transatlantic Telegraphic Radio Transmission

First Practical Photoelectric Cell Is Developed

First Demonstration of Transatlantic Radiotelephony

Radio Broadcasting Begins