Guglielmo Marconi 

Early Radio

James Clerk Maxwell developed the first radio-wave theorem in 1864. He proved, mathematically, that if an electrical interruption is of short distance from the point at which it occurred, there would be effect or passage of electrical current due to "some sort of waves that move at the speed of light", in which the electromagnetic energy would travel.

Heinrich Hertz experimented with Maxwell’s thesis in 1888. He demonstrated that "waves traveled in straight lines and that they could be reflected by a metal sheet". He tested with two conductors separated by a short gap (5ft). This idea was also advanced by the Italian physicist Guglielmo Marconi, who successfully repeated Hertz’s experiments with a spark gap of 30ft.

Augusto Righi, an Italian physicist, continued and refined Hertz’s work establishing the equality between electrical and optical vibrations. Another scientist, Temistocle Calzecchi-Onesti, constructed, in 1888, a "tube" due to his belief that electrical discharges of atmospheric perturbations influence iron filings.

In 1894, Oliver Lodge named Temistocle’s  famous "tube" the "coherer" and increased the reception gain of the hertzian waves. Then, the Russian, Alexander Popoff, created a vertical metal pole by using Lodge’s coherer and collected atmospheric disturbances in a rudimentary antenna. The invention of these instruments helped Guglielmo Marconi verify the fact that electromagnetic waves can travel between two points separated by an obstacle. This led to the creation of the first radio transmitter. This experiment was repeated with larger spark gaps (5 ft expanded to 100 km). Thus, radiotelegraphy was born.

Marconi at Signal Hill, just after
receiving the first wireless signal to
cross the Atlantic, December 12, 1901