It's more Broadcast than Ham related but never the less both mix at some point!
More info here:
Here's a list of some important dates for radio from the Unesco site:
".....22 February 1857 : Birthday of Heinrich Rudolf Hertz, a German physicist who clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell. He was the first to satisfactorily demonstrate the existence of electromagnetic waves by building an apparatus to produce and detect radio waves. His achievements triggered the invention of the wireless telegraph and radio.
30 November 1858 : Birthday of Jagdish Chandra Bose, a pioneer of wireless broadcasting. Indian physicist, biologist, and early writer of science fiction, he pioneered the investigation of radio and microwave optics and laid the foundations of experimental science in the Indian subcontinent.
6 October 1866 : Birthday of Reginald Fessenden, inventor of audio broadcasting and radio pioneer.
25 April 1874 : Marconi’s date of birth.
7 May 1895 : Russian inventor Alexander Popov’s first demonstration of his radio receiver to the Russian Physical and Chemical Society. The date is celebrated in the Russian Federation and Bulgaria as "Radio Day".
28 March 1896 : Anniversary of Marconi's first audio transmission. (Marconi is known for his development of the telegraph and we have found no evidence of a first in audio transmissions).
2 June 1896 : Marconi patented a radio device.
27 July 1896 : Marconi's first public wireless transmission of Morse code....."
Have a nice week!