Eventful Dates in Radio Development:

1727 Cuneus and Musschenbroek (Dutch) discovered the principle
of the capacitor.
1842 Joseph Henry (U.S.) experimented with induced voltages.
1850 Faraday (English) performed experiments similar to those
of Joseph Henry.
1867 Clerk Maxwell (Scottish) showed mathematically that light
is an electromagnetic wave and predicted that there must be
other electromagnetic waves at different frequencies.
1874 Ferdinand Braun (German) discovered the rectifying action
of some crystals.
1879 Hughes (English) heard wireless waves but could not explain
them to the Royal Society.
1884 Edison (U.S.) observed the Edison effect.
1187-9 Heinrich Hertz (German) developed a spark transmitter using
a capacitor with plates fairly wide apart. He developed the
first wireless detector.
1889 Sir Oliver Lodge (English) developed the principle of tuning
based on the previous work of Michael Pupin (U.S.).
1890 Branly (French) developed the Branly coherer, a form of
detector, based on the earlier work of Guitard (French).
1894 Marconi (Italian) developed an antenna and ground system,
using the Branly coherer. He radiotelegraphed over a
distance of two miles.
1901 Marconi sent a signal from England to Newfoundland, using a
detector invented by Lieutenant Solari (Italian).
1902 Fessenden (U.S.) developed the continuous-wave system with
radio-frequency alternators.
1902 Poulsen (Denmark) worked out another continuous-wave system
with an arc.
1904 J. A. Fleming (English) developed the Fleming valve.
1906 General Dunwoody (U.S.) devised a crystal detector.
1907 Lee De Forest (U.S.) developed the triode with a control grid.
1907 E. H. Armstrong (U.S.) developed the regeneration principle
for receivers and transmitters.
1909 The steamship 'Republic' sank, January 23. People were
rescued for the first time through the use of radio. Radio
was popularized.
Recent Hazeltine (U.S.) developed the neutrodyne receiver.
Recent Armstrong (U.S.) developed the superheterodyne and
frequency-modulation receiver.

(Source of the above information - "Elements of Radio" - 4th Ed.(1959)
by Abraham Marcus & William Marcus, published by Prentice-Hall Inc.)

----------- Early Days of Wireless - #14 ------ de Gil, VE4AG ------