Early telegraphs relied on wires connecting stations with direct current providing the operating signal. Experimenters tried various methods of wireless telegraphy in an effort to span the oceans, but none were successful until Guiglielmo Marconi made the first trans-Atlantic transmission in 1901. His work was based on that of earlier researchers.
When Thomas Edison developed the first practical light bulb, he found that a current would pass through vacuum when a positively charged plate was included inside the glass envelope. We know now that the heated filament caused negatively charged electrons to “boil” from its surface, but until electron theory was advanced fifteen years later, Edison could not explain how it happened. The discovery had enormous implications, yet curiously, Edison did not pursue it.
John Ambrose Fleming worked for both Edison and Marconi. He perfected Edison’s earlier device, adding a separate plate over the filament, now called a cathode. Fleming patented the “Fleming Valve”, a diode that was used as a detector for early spark radio transmissions. Spark is now prohibited by international agreement because its extremely broad signal causes widespread interference.
Lee De Forest introduced a metal grid between the cathode and anode, allowing a relatively small voltage to control a large current. His triode tube was the basis of the first amplifier. De Forest found that series-connected amplifiers provided vastly increased gain.
The work of these men contributed to the dawn of radio communications, and later, the development of television and radar. It’s hard to imagine now, but in the 1920s and 1930s, a radio was a high-tech home appliance similar to a laptop computer with an internet connection.
The Second World War spurred the pace of electronic design. At Bell Labs, John Bardeen and Walter Brattain fabricated the first working transistor, a point contact design that was difficult to make and highly fragile. It was a crystal version of De Forest’s triode. William Shockley, also at Bell Labs, built a solid-state diode using a nearly pure germanium crystal that would find use as a mixer in a radar set. After the war, he worked to produce the first transistor capable of mass production. In 1956, all three men received the Nobel Prize in physics.
Transistors replaced the mechanical switches used to program early computers. Discrete transistors were still relatively large, but the space race lead directly to the integrated circuit, combining numerous transistors on one compact device. The drive for ever-increasing numbers of transistors continues today, with billions of transistors on a single chip.