As Nelson explains in The History of Television Technology, Electronically scanning systems were independently and almost simultaneously developed in the 1920's and '30's. Utilizing such inventions as the German cathode-ray tube and the iconoscope, two American researchers invented the electronic television system. Television sets, computers, automated teller machines, video game machines, video cameras, monitors, oscilloscopes and radar displays all contain cathode-ray tubes; they operate based on a screen that emits a visible light when struck by a beam of electrons. Russian scientists attached this technology to a camera, and using mirror-drum scanning transmitted crude geometrical patterns onto the first television screen, called the iconoscope. Mirror-drum scanning was a light, efficient, mechanical scanner and in its original form there were as many mirrors as there were lines in the picture and each mirror was tilted at a different angle compared to the axis of the drum. As it rotated each mirror caused a line to be scanned below or beside the previous one.
These two new inventions paved the way for American television's first public broadcast at the New York World's Fair in 1939. RCA,