No single inventor
Few inventions are credited to as many people as radio. Textbooks often name Guglielmo Marconi, schools in some countries teach Alexander Popov or Nikola Tesla, and historians prefer to describe a chain of discoveries in which each person contributed something different. The question “who invented radio?” depends on what you count: the theory, the proof that radio waves exist, the first signal sent, the first practical system, or the first business.
Theory: Maxwell
The foundation was theoretical. In the 1860s, the Scottish physicist James Clerk Maxwell worked out a mathematical description of electricity and magnetism. His equations, published in full form in 1873, implied that electric and magnetic disturbances should travel through space as waves, at a speed matching the measured speed of light. Maxwell concluded that light itself was an electromagnetic wave. He did not demonstrate other kinds of waves in a laboratory, and his theory was not accepted everywhere at first.
Proof: Hertz and the experimenters
Heinrich Hertz, a German physicist, set out to test Maxwell’s ideas in the second half of the 1880s. He used an induction coil to create sparks across a gap, and a nearby loop of wire with a small gap as a detector. When a spark jumped at the transmitter, a smaller spark could appear at the receiver across the room. By measuring the waves’ properties, he showed that they reflected, refracted and polarized like light, and that they traveled at a finite speed. His results, published around 1887 to 1889, confirmed Maxwell’s prediction. Hertz did not see a practical use for the waves, and he died young in 1894. The unit of frequency, the hertz, is named after him.
Others carried the experiments forward in the 1890s. In Britain, Oliver Lodge worked on detecting the waves and tuning circuits, and he demonstrated signaling in 1894. Édouard Branly in France had found that metal filings in a tube change their electrical resistance when exposed to the waves, and Lodge developed this into the coherer, a sensitive detector. In India, Jagadish Chandra Bose studied very short radio waves and developed detectors, including a semiconductor-type device. Augusto Righi in Italy investigated Hertz’s waves, and his writings were known to young Marconi.
Wireless telegraphy: Popov, Marconi and Tesla
Taking Hertz’s waves and turning them into a signaling system was the next step. The aim, called wireless telegraphy, was to send messages without wires, in competition with the electric telegraph.
- Alexander Popov in Russia built a lightning detector and receiver in 1895 and reported it to the Russian Physical-Chemical Society. Soviet histories later gave him priority as inventor of radio, a claim that is debated.
- Guglielmo Marconi began experiments in Italy in 1895. He combined existing parts, including the coherer, a transmitter with an antenna and a ground connection, and a telegraph key and printer, into a practical system. After moving to Britain in 1896 he patented his work, founded a company, and gradually increased the range. In December 1901 he and his assistants reported hearing the letter “S” in Morse code sent from Cornwall at a receiver in Newfoundland. Some engineers at the time were skeptical, and later analysts have debated whether the signal was really heard, though most historians think a transatlantic transmission was feasible.
- Nikola Tesla demonstrated radio-controlled boats in 1898 and gave public lectures on wireless in the early 1890s. He patented tuned circuits in the late 1890s. Tesla envisioned wireless power transmission, and his later projects were not successful, but his earlier patents on tuning were important.
The patent disputes
Marconi’s company obtained patents on wireless telegraphy and fought many legal battles over them. In 1943, a United States Supreme Court decision in a case involving the Marconi company canceled some of his patent claims on the grounds that earlier work, including that of Lodge, Tesla and John Stone Stone, anticipated them. That case is often cited in popular accounts as proof that Tesla invented radio. It was actually a ruling about particular patents and a government contract dispute, and it did not make a general judgment about who deserves credit for the invention. The truth is more nuanced: Marconi’s system combined several known techniques, and the others had made important contributions of their own.
In 1909, Marconi shared the Nobel Prize in Physics with Karl Ferdinand Braun, who had improved transmitters by coupling circuits to extend range and sharpen tuning.
Why the credit is so tangled
Several factors explain the disagreements.
- Many people worked on similar ideas at the same time, and it was easy to arrive independently at the same device.
- Patents rewarded those who filed first and had capital, not necessarily those who thought of the idea first.
- National pride shaped histories, as Italian, Russian, British, American, Indian and other accounts each emphasize a different figure.
- The point at which “invention” is declared is arbitrary. The pieces were gradually assembled.
From signals to services
By 1900, wireless telegraphy was in regular use at sea, offering what even submarine cables could not, since ships could be reached. There, ships could contact each other and the shore, and shortly afterward it became standard equipment on passenger vessels. The next developments, such as the vacuum tube, amplitude modulation and speech transmission, changed the field from point-to-point signaling toward what became radio broadcasting. Radio’s early story is one of science moving into engineering, with cooperation, rivalry and legal fights all mixed together. A fair summary is that Maxwell predicted the waves, Hertz proved them, and Lodge, Popov, Marconi, Tesla and many others made them useful.