laboratory when they impulsively decided to conduct an experimental broadcast of the William Tell overture. An astonished wireless operator in Brooklyn Naval Yard, four miles away, who could not understand why he was getting music through his headset intercepted the transmission, and the radio tube was born. By the end of World War I, radio tubes were mass-produced. The term radio derived from the fact that transmitters radiate signals in all directions and, by 1912, the term replaced the word wireless. It was around that time that David Sarnoff, the legendary promoter of American television, began his rise through the ranks of the Marconi Wireless Company. Sarnoff emigrated from Russia to the US in 1900. In 1919, Sarnoff left Marconi to join the newly formed Radio Corporation of America (RCA). By 1920, RCA had launched two radio stations, KDKA of Pittsburgh and WWJ of Detroit; they were soon making regular broadcasts. Within the next two years, radio experienced explosive growth that only that of its cousin, television (and much later, the Internet), surpassed. SPINNING DISKS AND SHOOTING ELECTRONS During this same era, the foundation for today's visual communications systems emerged. No one individual deserves the credit for inventing the television-as was true with radio, it was a collective, although not always cooperative, effort. The process may have started in the 1870s when a couple of British telegraphy engineers discovered some intriguing properties of the element selenium. In their experiments, selenium conducted electricity better when it was exposed to a light source than when it was left in darkness. They developed this discovery into a system in which they place a source of light at one end of a circuit and selenium at the other. If an object passed between the light and the selenium, it would interrupt the flow of electricity. By combining a group of these circuits, they used selenium to create a mosaic of light. Many inventors, not the least of whom was Alexander Graham Bell, began experimenting 