TV / Television
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Historically, no single person can be credited with the invention of television, as the perfection of the modern television system was the result of a number of isolated discoveries in the related fields of electricity, electromagnetism, and electrochemistry.
Although television is based on photoelectric technology, its initial developments are linked to pioneering attempts in the mid-19th century to send still images down a telegraph wire.
In 1873, Louis May, a British telegrapher, discovered what we consider today to be the basics of photo-conductivity, as he found that bars of selenium, when exposed to light, were a strong conductor of electricity. He also noted that the conduction of electrical current would vary depending on the amount of light hitting the selenium bars.
The final links between telegraphs and television occurred with M. Senlacq of Ardres, France in 1878, who proposed that the changes in electrical voltage produced by selenium when scanning a document, could magnetically control a pencil at the receiving end of the transmission. By 1881, British pioneer Shelford Bidwell had successfully transmitted silhouettes using both selenium and a scanning system, and had called the device the scanning phototelegraph.
Meanwhile, in 1875 the American scientist George R. Carey in Boston developed a way of using electricity to pick up an image at the back of a camera and show it a great distance away, based on the assumption that each element of the picture would be transmitted simultaneously, each over a separate circuit.
Carey's idea was to use dozens of light-sensitive selenium cells (later known as photoelectric cells) arranged in a mosaic, and connected to a battery; each cell would respond to the intensity of light (the picture or scene) focused on the "transmitter", and would allow a greater or lesser current to flow down the wire which connected each one to a lamp on a corresponding spot on the "receiver" or screen. Electromagnets connected to each of the lamps on the receiver plate were to regulate the amount of light on each section.
However, for a recognizable picture, hundreds of cells, lamps and wires were needed (even to match the poor quality of a newspaper photograph 15,000 individual connections would be required for a two-inch square picture), and this approach thus proved impractical.
Early television experimenters therefore began to realize that the ideal system would be electric, and would consist of one light cell connected by a single pair of wires to one lamp - the idea being that a cell in a camera should record the brightness of each part of the picture in turn, and the lamp at the other end should be able to reproduce each point at the correct intensity.
Meanwhile, in 1880 the important principle - subsequently adopted in all forms of television - of rapidly scanning each element in the picture in succession, line by line and frame by frame (with reliance on the persistence of human vision), was proposed independently by W.E. Sawyer in the United States and Maurice Leblanc in France. This established the possibility of using only a single wire or channel for transmission.
Then, in 1884 the German university student [development aided by] Nipkow* proposed and patented the world's first electromechanical television system, in which a
disc containing a spiral of holes spun around a high speed between an image and the photoelectric (selenium) cell.
As the disc spun, only one point of the image was exposed to the cell at a time - having the effect of dividing it into lines - but the whole image would be covered for each revolution of the disc. At the receiving end a lamp, controlled by the photoelectric cell, would vary rapidly in brightness, and beyond that a second Nipkow disc would spin round at precisely the same speed and in synchronization with the first disc, its holes allowing light from the lamp to be projected on to only one part of the receiver's screen at any time - corresponding with an identical part in the original image. As the disc rotated, the eye would then blur all the points together, and see a reproduction of the full image on the screen.
[Early development by] John Logie Baird* in London in 1926, succeeded in transmitting images using Nipkow discs in both camera and receiver. In the U.S. in November 1928, television visionary David Sarnoff of RCA - inspired by the mechanical systems pioneered by Baird, and Ernst Alexanderson and Charles Francis Jenkins in the U.S. - announced "The Dawning Age of Sight by Radio".
However, the following year Sarnoff met the young Russian electronics engineer [early development by] Zworykin*, who had plans for an entirely electronic system for television, and immediately Sarnoff hired him for RCA, and Zworykin became a major developer of electronic television and RCA's greatest engineer.
Electronic television is based on the development of the cathode ray tube. In 1897, German physicist [related to work of] Braun* was investigating the behaviour of electrons - the tiny particles which carry electric current - and found that when electrons collided with fluorescent paint, the paint glowed brightly. He then spread paint over the end of a modified cathode-ray tube (now known as a Braun tube, or cathode-ray oscilloscope), and by positioning electromagnets and electrically charged plates outside the tube, focused the beam of electrons (cathode ray) so that it produced a bright spot of light on the flourescent end of the tube. By varying the voltage applied to the electromagnets and plates he could make the spot move about on the screen.
This was the cathode-ray tube that became the basis of modern television cameras and receivers.
Braun's tube was then used by Boris Rosing, professor of physics at the University of St. Petersburg. Applying Nipkow's disc of 1884 to pick up the image and convert it into an electrical signal, he then used this signal to control the brightness of the cathode-ray spot, which was made to move up and down the screen along parallel lines in a fraction of a second. Even though by 1911 Rosing was still only able to produce very crude pictures, his was almost certainly the world's first working television system.
In 1908, and again in 1911, a completely electronic television system was proposed by the Scottish electrical engineer [early development by] Swinton*, who theorized that not only should a cathode-ray tube be used as a receiver, as in Rosing's model, but also that a modified tube could be developed for a television camera. The image would be focused on the end of the tube, which would be made of a light-sensitive material, and as the cathode ray scanned in parallel lines across the photocell screen, the electrical signal from the tube would match exactly the intensity of light at each point.
However, Swinton's system remained a theory only, and it was not until the work of Vladimir Zworykin that the first electronic camera tube (the iconoscope) was developed between 1923 and 1931.
Zworykin (who worked at Westinghouse) had been one of Rosing's electrical engineering students at St. Petersburg. His work proved that Swinton's ideas had been valid, and by the end of 1923 he had produced a picture display tube, the kinescope, as well as the prototype iconoscope. The equipment was very basic and could show nothing more complex than a simple cross projected on the camera tube, and Westinghouse officials were not impressed.
In 1929 Zworykin moved to RCA, developed the iconoscope as a fully practical tube, and his entire electronic television system became the basis of the modern television system. Meanwhile, simultaneously [early development by] Farnsworth*, an American engineer, was working independently towards an electronic scanning system along the same lines as Zworykin's iconoscope and, after a three-year battle with RCA, Farnsworth was awarded the patent for his pickup tube, the equivalent of Zworykin's kinescope.
In 1927, pictures of Herbert Hoover were transmitted by radio and telephone line for 200 miles (from Washington D.C. to New York) in the first televised speech using equipment based on the same mechanical principle as the systems of Baird and Jenkins, and the following year Baird showed the first color pictures on television.
In 1928 experimental broadcasts started in the U.S. from a transmitter set up by Ernst Alexanderson of General Electric at Schenectady, New York using mechanical scanning, as did another experimental station set up by RCA in New York City the same year. RCA's first television star, a model of Felix the Cat, was seen in a special demonstration by people more than 1,000 miles away in Kansas.
In Britain in 1928, Baird was extending his system by transmitting a signal between London and New York, and in 1929 the British Broadcasting Service (BBC) adopted the Baird mechanical system and the world's first television studio was opened in London. Baird's electromechanical system consisted of a light sensitive camera behind a rotating disc, and delivered only a crude picture consisting of 30 lines at twelve frames per second to a television receiver that displayed an uneven and tiny orange and black image.
However, because the pictures carried so little visual information, it was possible to broadcast them from ordinary medium-wave radio transmitters, which can travel thousands of miles. Baird's pictures of dancers, singers and actors were occasionally picked up in America, and in 1930 the BBC lent him a second transmitter, so he could also send sound with the pictures. By 1932 John Logie Baird had developed the first commercially viable television system and had sold 10,000 sets.
In 1931, Zworykin made his first practical version of his iconoscope electronic camera, and three years later two British electronic firms, EMI and Marconi, independently created an all-electronic television system, EMI making the cameras and receivers and Marconi G the transmitters and aerials.
This electronic system was officially adopted in England by the BBC in November 1936, becoming the world's first public high definition service, which provided improved picture quality to 405 horizontal lines, with 25 complete pictures each second. Three years later, fully electronic broadcasting started in the United States, with RCA broadcasting pictures of President Roosevelt at the opening of the 1939 New York World's Fair.
Oneliner: Television is a mass medium for advertising, entertainment, news, and sports.
Bibliography:
- Encyclopedia Britannica.
- Collier's New Encyclopedia.
- Abramson, Albert, A History of Television, London, 1987.