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Facsimile TransmissionMany systems have been devised for electrically transmitting drawings, figures, photographs, or other information over wire lines and cables, or by radio. A system of facsimile for transmission over wire circuits72 was placed in commercial operation over telephone lines in 1925. This was replaced in 1935 by an improved method73 which involved modulation by optical means. Picture transmission for news purposes by both wire and radio methods now is commonplace. The principle involved in many systems of facsimile transmission is to revolve slowly a cylinder on which the picture or other information to be transmitted is attached. In some systems a light beam and phototube are used to convert the "lights" and "shades" of the image into electric signals. In other systems, a special paper (page 339) is employed. At the receiving station a synchronized reverse process is used to record the information by recreating; on paper, an image of the material scanned.
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Last Update: 2011-06-05