1831

Discovery and theory of induction by Michael Faraday and Joseph Henry.

1888

Radio waves detected and measured by Heinrich Hertz.

1890

Edouard Branly (1844-1940) invents a device, a "coherer," that becomes conducting in the presence of natural electric disturbances, such as lightning. (Powdered metal particles that attract one another as a field induces minute currents in them).

1892

William Preece (1834-1913), using loops of wire several hundred feet long, detects current interruptions in one with the other..

1894

Oliver Lodge (1851-1940) is first to employ the Branly coherer to sense "Hertzian waves" (radio waves).

1895

Nikola Tesla is listening around New York to signals produced by high-frequency alternators at his Fifth Avenue laboratory. By tuning several sources at slightly separated frequencies, he is able to monitor the transmission at an audible beat frequency. In 1897, the year of his basic radio patent (U.S. No. 645,576), he is able to pick up a signal at West Point, 30 miles from his transmitter. (Tesla coils are in general use to power everyone's radio transmitters through the early years of the twentieth century.) He demonstrates a radio-controlled boat at Madison Square Garden in 1898.

1896

Aleksandr Popov (1859-1906) transmits radio signals between buildings at the University of St. Petersburg.

1896

Guglielmo Marconi (1874-1937) sends a radio signal nine miles across the Bristol Channel. In 1901, after weeks of effort, he sends a recognizable signal from England to Newfoundland, the first transatlantic wireless communication.

1899

Ferdinand Braun (1850-1918) contributes a "sparkless" antenna to the Marconi system, and shares with Marconi the Nobel Prize for Physics in 1909.

1902

Reginald Fessenden (1866-1932) conceives of "heterodyning" to simplify and improve radio receivers, though the principle wasn't of real use until De Forest's invention of the triode. (Two radio frequencies are beat together to give a single "intermediate" frequency.) He is first to broadcast speech and music, in 1906.

1904

John Fleming (1849-1945) produces the first vacuum-tube "diode detector," then known as the "thermionic valve."

1906

Lee De Forest (1873-1961) invents the three-element vacuum tube, or triode, making better signal processing and amplification possible. He called it an "audion."