with selenium. In 1880, Bell invented something he called the photophone. It used selenium to transmit a visual display of the frequencies that comprised the human voice. It is astonishing that Bell overlooked the potential of image transmission. However, Bell's priority was to leverage another medium to simulate sound SO that his deaf wife could better communicate. The History and Technology of Analog Video Green A color scanning disk TV camera Color scanning disk Figure 5-2. Nipkow Disk (Michel Bayard). Nipkow, a German university student in Berlin, became entranced with the idea of image scanning. He developed a spherical disc that he perforated with holes. He positioned the apertures of the disk such that, as the disc revolved at a specific speed, each hole swept over a segment of a picture (Figure 5-2). When rotated between an object and a light source, it reproduced a crude electrical representation of the original object by responding to variations in light. The concept provided a framework for reproducing images with electrical signals, but it was too slow to offer passable picture quality. Nevertheless, the invention earned Nipkow, in 1883, German patent number 30,105, "The master patent in the television field." In 1893, Archibald Campbell-Swinton, a Scottish engineer, made an address to the Roentgen Society in which he outlined plans for an electronic television system that was remarkably similar to that which the British Broadcasting Company (BBC) adopted, in 1937. Campbell-Swinton never made a television or similar apparatus; his work was purely theoretical. In 1907, a German professor, Boris Rosing of the Technical Institute of St. Petersburg, became interested in understanding how images could be produced using electrical means. His research led him to develop a prototype device-the first cathode ray tube or CRT. Using a rotation-mirror image to transmit a signal that it received with a cold-cathode picture tube, it produced crude outlines of shapes. Magnetic coils generated the scanning signals th