A television system, by definition, transmits and receives live, moving half-tone images. Early versions, such as those invented by John Logie Baird in the 1920s, used crude, electromechanical, spinning, perforated, scanning discs to record and subsequently produce the images. The first transatlantic images were transmitted with this system in 1928.
Television relies on the fact that the human brain can convert a sequence of slightly different still images into a moving picture if more than fifteen frames are received every second. As soon as the number drops below fifteen, the motion looks jerky.
Today's televisions are a product of the invention of the cathode ray tube. This is coated with a phosphor that glows when an electron beam hits it. Behind the phosphor is a shadow mask that divides the image into picture elements (pixels). Television sets typically have 525 lines down the screen and these are raster scanned every sixtieth of a second. The scanning is interlaced so that odd-numbered lines are "painted" on one scan and even-numbered lines on the next.
In 1926 Philo Farnsworth (1906-1971) developed the world's first all-electronic system, where, like today, the cameras scan electronically and the television receiver is scanned electronically, too. By 1936 the BBC was producing 405-line, high-resolution images using this system. By 1949, ten million monochrome televisions had been sold in the United States, and now the average American spends between two and five hours per day "glued to the tube."The breakthrough in U.K. television watching was the broadcast of the coronation of Queen Elizabeth II in June 1953.
