at the tube required. It was the world's first glimpse of television. Video Communications: The Whole Picture Although Rosing's CRT produced only faint patterns with no light or shade, it attracted the attention of one of his students, Vladimir Kosma Zworykin. Fascinated with the CRT, Zworykin continued to perfect it after immigrating to America, in 1917. While employed at Westinghouse, in 1923, he filed a patent for a television receiver. By 1924, he was able to demonstrate the technology-a seven-inch CRT with electrostatic and electromagnetic deflection to steer an electron beam. This first picture tube was SO crude that it could barely transmit a single character. Nevertheless, it proved a fundamental component of the television system that Zworykin proceeded to invent. Next, Zworykin developed an improved image-scanning device. It replaced Nipkow's mechanical disc with an electronic one. Combining the Greek words icon (image) and scope (to watch), Zworykin named the invention an iconoscope (Figure 5-3). It was a CRT with a lens on an angled shaft. At the back of the device, an electron gun focused a beam of electrons on a target that consisted of a mica plate that was covered with tiny photosensitive cesium-silver droplets. The beam of electrons varied in accordance to the light captured from the original image. The beam energized the cesium-silver droplets as it passed over them. The change in their charge induced a current in the signal plate, and varied in relation to the lights and shadows along each line of the picture. The result was a coded signal that traversed a transmission path to a television's picture tube, which decoded it. The original image was recreated from behind, and appeared on the screen as a series of glowing dots that formed a picture. In 1925, Zworykin filed a patent application for his electronic television system. That same year, an American inventor named Charles Jenkins used mechanical means (Nipkow's disc) to produce a system that transmitted a picture of a waving hand. The signa