The history of television

For ages Man dreamt about the possibility of transmitting pictures over great distances, but not until he had learnt to master the electron was there any real hope of turning dream into practical reality.Different experiments by various people, in the field of electricity and radio, led to the development of basic technologies and ideas that laid the foundation for the invention of television.
1873. Ireland. A young telegraph operator, Joseph May, discovered the photoelectric effect: selenium bars, exposed to sunlight, show a variation in resistance. Variations in light intensity can therefore be transformed into electrical signals. That means they can be transmitted.
1875. Boston, USA. George Carey proposed a system based on the exploration of every point in the image simultaneously: a large number of photoelectric cells are arranged on a panel, facing the image, and wired to a panel carrying the same number of bulbs.
In France in 1881, Constantin Senlecq published a sketch detailing a similar idea in an improved form: two rotating switches were proposed between the panels of cells and lamps, and as these turned at the same rate they connected each cell, in turn, with the corresponding lamp. With this system, all the points in the picture could be sent one after the other along a single wire.
In 1884 a German inventor named Paul Nipkow patented a system that did it with two disks, each identically perforated with a spiral pattern of holes and spun at exactly the same rate by motors. The first whirling disk scanned the image, with light passing through the holes and hitting photocells to create an electrical signal. That signal traveled to a receiver (initially by wire) and controlled the output of a neon lamp placed in front of the second disk, whose spinning holes replicated the original scan on a screen. In later, better versions, disk scanning was able to capture and reconstruct images fast enough to be perceived as smooth movement�at least 24 frames per second. The method was used for rudimentary television broadcasts in the United States, Britain, and Germany during the 1920s and 1930s.
But all-electronic television was on the way. A key component was a 19th-century invention, the cathode-ray tube, which generated a beam of electrons and used electrical or magnetic forces to steer the beam across a surface�in a line-by-line scanning pattern if desired. In 1908 a British lighting engineer, Campbell Swinton, proposed using one such tube as a camera, scanning an image that was projected onto a mosaic of photoelectric elements. The resulting electric signal would be sent to a second cathode-ray tube whose scanning beam re-created the image by causing a fluorescent screen to glow. It was a dazzling concept, but constructing such a setup was far beyond the technology of the day. As late as 1920 Swinton gloomily commented: "I think you would have to spend some years in hard work, and then would the result be worth anything financially?"
A young man from Utah, Philo Farnsworth, believed it would. Enamored of all things electrical, he began thinking about a similar scanning system as a teenager. In 1927, when he was just 21, he successfully built and patented his dream. Philo had created the first electronic television system, which did away with the rotating disks and other mechanical aspects of mechanical television. Thus was born the television system which is the basis of all modern TVs. But as he tried to commercialize it he ran afoul of the redoubtable David Sarnoff of RCA, who had long been interested in television. Sarnoff tried to buy the rights to Farnsworth's designs, but when his offer was rebuffed, he set about creating a proprietary system for RCA, an effort that was led by Vladimir Zworykin, a talented electrical engineer from Russia who had been developing his own electronic TV system.
After several years and massive expenditures, Zworykin completed the job, adapting some of Farnsworth's ideas. Sarnoff publicized the product by televising the opening of the 1939 World's Fair in New York, but in the end he had to pay for a license to Farnsworth's patents anyway.
In the ensuing years RCA flooded the market with millions of black-and-white TV sets and also took aim at the next big opportunity�color television.