Overview

Television became one of the technical marvels of the twentieth century because it can produce moving images, voice, and music all on the same receiver. Crude television broadcasting based on mechanical scanning had been demonstrated before the turn of the century, but it was not until 1928 that the first television programs were broadcast in the United States. Those early systems depended on cumbersome and unreliable mechanical spinning disks to produce a picture. Modern television, however, depends on the compatible combination of a camera and picture tubes that are based on the synchronized scanning of electron beams.

The first cathode-ray tube, an evacuated glass envelope containing an electron-emitting cathode and a positively charged anode, was developed as a laboratory tool for investigating electrical phenomena in gases and in vacuum. An early version of the tube made possible the discovery of X-rays. Years later, researchers found that the electron beam could be scanned over a fluorescent screen by switching the polarities of internal electrodes to form images that remained long enough to be viewed. This discovery led to the invention of the oscilloscope.

But it was not until the iconoscope was developed that modern television became a reality. Instead of having the electron beam paint an image on a phosphor screen, the polarities of the internal electrodes were switched so that the beam scanned an optical image focused on an internal plate. The electrical signal taken from the plate was modulated by the electron beam so that it conveyed the...