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A History of Television by Andrew Roper. For a long time we have dreamnt of transmiting images or pictures over a great distances , but notuntil he had learnt to master the electron was there any real hope of turning dream into practicalreality. And it all happened by chance... The foundations 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 intensitycan therefore be transformed into electrical signals. That means they can be transmitted. ���������������������������� The photoelectric effect 1875. Boston, USA. George Carey proposed a system based on the exploration of every point in theimage simultaneously: a large number of photoelectric cells are arranged on a panel, facing theimage, and wired to a panel carrying the same number of bulbs. ����������������������������� George Carey's idea This system was impracticable if any reasonable quality criteria were to be respected. Even tomatch the quality of cinema films of that period, thousands of parallel wires would have beenneeded from one end of the circuit to the other. In France in 1881, Constantin Senlecq published a sketch detailing a similar idea in an improvedform: two rotating switches were proposed between the panels of cells and lamps, and as theseturned at the same rate they connected each cell, in turn, with the corresponding lamp. With thissystem, all the points in the picture could be sent one after the other along a single wire. Thisis the basis of modern television: the picture is converted into a series of picture elements.Nonetheless, Senlecq's system, like that proposed by Carey, needed a large number of cells andlamps. 1884, the German Paul Nipkow applied for a patent covering another image scanning system:it was to use a rotating disk with a series of holes arranged in a spiral, each spaced from thenext by the width of the image; a beam of light shining through the holes would illuminate eachline of the image. ���������������������������� Paul Nipkow (1860-1940) ������������������������������� Nipkow's System The light beam, whose intensity depended on the picture element, was converted into an electricalsignal by the cell. At the receiving end, there was an identical disc turning at the same speed infront of a lamp whose brightness changed according to the received signal. After a completerotation of the discs, the entire picture had been scanned. If the discs rotated sufficientlyrapidly, in other words if the successive light stimuli followed quickly enough one after theother, the eye no longer perceived them as individual picture elements. Instead, the entirepicture� was seen as if it were a single unit. The idea was simple but it could not be put intopractice with the materials available at the time. Other scientific developments were to offer analternative. The electron, the tiny grain of negative electricity which revolutionised physicalscience at the end of the 19th century, was the key. The extreme narrowness of electron beams andtheir absence of inertia caught the imagination of many researchers and oriented their studiestowards what in time became known as electronics. The mechanical approach nevertheless stood itsground, and the competition lasted until 1937. The cathode ray tube with a fluorescent scene wasinvented in 1897. Karl Braun, of the University of Strasbourg, had the idea of placing twoelectromagnets around the neck of the tube to make the electron beam move horizontally andvertically. On the fluorescent screen the movement of the electron beam had the effect of tracingvisible lines on the screen. A Russian scientist, Boris Rosing, suggested this might be used as a receiver screen and conductedexperiments in 1907 in his laboratory in Saint Petersburg. As early as 1908 the Scotsman A. A. Campbell Swinton outlined a system using athode ray tubes atboth sending and receiving ends. This was the first purely electronic proposal. He published adescription of it in 1911 the image is thrown onto a photoelectric mosaic fixed to one of thetubes; a beam of electrons then scans it and produces the electric signal; at the receiving end,this electric signal controls the intensity of another beam of electrons which scans thefluorescent screen.A History of Television by Andrew Roper. For a long time we have dreamnt of transmiting images or pictures over a great distances , but notuntil he had learnt to master the electron was there any real hope of turning dream into practicalreality. And it all happened by chance... The foundations 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 intensitycan therefore be transformed into electrical signals. That means they can be transmitted. ���������������������������� The photoelectric effect 1875. Boston, USA. George Carey proposed a system based on the exploration of every point in theimage simultaneously: a large number of photoelectric cells are arranged on a panel, facing theimage, and wired to a panel carrying the same number of bulbs. ����������������������������� George Carey's idea This system was impracticable if any reasonable quality criteria were to be respected. Even tomatch the quality of cinema films of that period, thousands of parallel wires would have beenneeded from one end of the circuit to the other. In France in 1881, Constantin Senlecq published a sketch detailing a similar idea in an improvedform: two rotating switches were proposed between the panels of cells and lamps, and as theseturned at the same rate they connected each cell, in turn, with the corresponding lamp. With thissystem, all the points in the picture could be sent one after the other along a single wire. Thisis the basis of modern television: the picture is converted into a series of picture elements.Nonetheless, Senlecq's system, like that proposed by Carey, needed a large number of cells andlamps. 1884, the German Paul Nipkow applied for a patent covering another image scanning system:it was to use a rotating disk with a series of holes arranged in a spiral, each spaced from thenext by the width of the image; a beam of light shining through the holes would illuminate eachline of the image. ���������������������������� Paul Nipkow (1860-1940) ������������������������������� Nipkow's System The light beam, whose intensity depended on the picture element, was converted into an electricalsignal by the cell. At the receiving end, there was an identical disc turning at the same speed infront of a lamp whose brightness changed according to the received signal. After a completerotation of the discs, the entire picture had been scanned. If the discs rotated sufficientlyrapidly, in other words if the successive light stimuli followed quickly enough one after theother, the eye no longer perceived them as individual picture elements. Instead, the entirepicture� was seen as if it were a single unit. The idea was simple but it could not be put intopractice with the materials available at the time. Other scientific developments were to offer analternative. The electron, the tiny grain of negative electricity which revolutionised physicalscience at the end of the 19th century, was the key. The extreme narrowness of electron beams andtheir absence of inertia caught the imagination of many researchers and oriented their studiestowards what in time became known as electronics. The mechanical approach nevertheless stood itsground, and the competition lasted until 1937. The cathode ray tube with a fluorescent scene wasinvented in 1897. Karl Braun, of the University of Strasbourg, had the idea of placing twoelectromagnets around the neck of the tube to make the electron beam move horizontally andvertically. On the fluorescent screen the movement of the electron beam had the effect of tracingvisible lines on the screen. A Russian scientist, Boris Rosing, suggested this might be used as a receiver screen and conductedexperiments in 1907 in his laboratory in Saint Petersburg. As early as 1908 the Scotsman A. A. Campbell Swinton outlined a system using athode ray tubes atboth sending and receiving ends. This was the first purely electronic proposal. He published adescription of it in 1911 the image is thrown onto a photoelectric mosaic fixed to one of thetubes; a beam of electrons then scans it and produces the electric signal; at the receiving end,this electric signal controls the intensity of another beam of electrons which scans thefluorescent screen.
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