The first vacuum tube was not made until the beginning of the 20th Century, but the foundations for its discovery were laid many years before.
It took many different developments to set in place all the foundations needed to be able to develop the vacuum tube or thermionic valve.
Each of these early discoveries set in place another stone ready for the ultimate invention of the thermionic vale or vacuum tube.
Obviously early discoveries of electricity pay their part, but others had a more direct bearing on more defined areas of technology that affected areas like the valve invention.
Professor Frederick Guthrie made one of the first discoveries in 1873. He was investigating effects associated with charged objects and he showed that a red-hot iron sphere that was negatively charged would become discharged. He also found that the same did not happen if the sphere was positively charged.
Interestingly Professor Guthrie had also mentored Ambrose Fleming who later patented the first diode valve. Guthrie was said to have been instrumental in turning Fleming's interest from chemistry to electricity. Guthrie also co-founded the Physical Society of London in 1874 - this Institute is now the Institute of Physics.
However progress towards the valve invention really started apace with the American inventor Thomas Edison. Edison was an inventor and had been developing many items associated with electricity. One major area of investigation was that of electric lighting.
Edison had not only been focussing on generating electricity but also on the incandescent lamps themselves. These lamps had proved to be very difficult to perfect. Not only did the filaments themselves have a sort life, but more importantly the inside of the glass envelopes became blackened.
It was known that the particles leaving the element were negatively charged, experiments were carried out to prevent them hitting the glass. One method that Edison tried involved placing a second element into the envelope. He reasoned that if he placed a positive charge on the second electrode, particles could be attracted away from hitting the glass of the bulb. In 1883 Edison experimented with the polarity of the charge on the second electrode and he noticed that when the second element was made positive with respect to the filament then a current flowed in the circuit. When the potentials were reversed he noticed that this did not happen. Edison was fascinated by the effect but uncharacteristically he did not find a use for it. Even so it became known as the Edison Effect.
Over the years Edison demonstrated the effect to many other leading scientific personalities including Preece, a well-known British electrical engineer and more importantly to Ambrose Fleming, the professor of electrical engineering at University College London. Although no developments were made for a number of years the seed had been sown for later discoveries.
Radio history timeline History of the radio Ham radio history Coherer Crystal radio Magnetic detector Spark transmitter Morse telegraph Valve / tube history Transistor Integrated circuit
Return to History menu . . .