Radio age (Jan-Dec 1926)

42 RADIO AGE for December, 1926 The Magazine of the Hour Art of Television Not Far Off Soon Will Attach Device to Set, to See Desired Events By ALBERT W. FRANKLIN* THE radio age is upon us. The electrical age, acknowledged by authorities to be still in its infancy, has been surpassed by the meteoric progress of the art of radio. This progress has in its scope the perfection of one most important invention to humanity — the art of television. Like the development of the moving pictures, television will follow the perfect transmission of photographs. Just when can be only a matter of time. At present there are several means of transmitting photographs from one point to another by wire, cable or radio. The various systems of themselves offer no solution to the problem of transmitting moving pictures. Nor has any one as yet proposed what appears to be a commercially feasible and practical solution. " From a logical viewpoint just what is the seemingly impossible barrier? Let us consider the systems. Caselli's 1856 Method OUTSTANDING advantages of the Belin system, the Bartlane, Hanson, A. T. & T., Leishman, Korn, R. C. A. or Jenkins system as compared to one another, are evident from a brief resume of their characteristics. As early as 1856 Caselli sent various designs by telegraphy, using for the transmitter a tinfoil-covered cylinder on which the designs were drawn in insulating compound. A needle acting very much like the stylus of a phonograph served the purpose of a contact pin traveling spirally oyer the surface of the revolving cylinder. Thus the circuit was made and broken as the lines passed under the contact pin, while at the receiving end, by an electro-chemical action, a similar cylinder synchronized with the transmitter reproduced the designs directly. ♦Chief Engineer, Chas. Freshman Co., Inc. Discovery of the effect of light on the electrical resistance of selenium became known in 1873 and shortly afterwards various, schemes to substitute selenium for Caselli's process were attempted. The most noteworthy were those of Semlocq and Perosino in 1878. After quite a lengthy interval Korn (in 1904) employing Semlocq's plan with several modifications, succeeded in transmitting photographs a few hundred miles. The method now in use by the R. A. C. is to place a negative of the photo on a glass cylinder. On this is focused a very narrow beam of light used as a stylus. By reflecting the varying intensity of the light passing through the cylinder the registry is effected and then follows an amplifier system which then allows the photo to be reproduced in several ways: either by a tape recorder which records the photo as a continuous line of dots and dashes; by means of a relay which operates a special pen and reproduces a pen and ink sketch, or by means of photographic reproduction, a light shutter being controlled by the current variations and controlling the light from a lamp focused on a sensitized rotating cylinder. Belin Full of Originality WITH such a system successful photo transmission has been accomplished by radio transmission from London to New York. The first photo which was transmitted over the Atlantic was sent by a system based upon the half-tone method of screening. The photo was automatically divided into a predetermined number of dots per square inch. A photo-electric cell then determined into which of eighteen groups a dot belonged, each group being given a distinguishing letter. By means of special relays, the letter was automatically transmitted and at the receiving station, the letter was converted into a dot and placed into its proper position in the photograph. Even though the photo was converted into 12,000 squares, much of its detail was lost. A more nearly perfect system is the Leishman process which employs a similar but modified principle and operates on trans-Atlantic cables. Perhaps the most original scheme is that developed by Belin. His process resolves itself upon the fact that bichromated gelatin becomes insoluble under strong light — his own discovery. Thus he places a film of wet gelatin under a negative whereupon the portions of the film swell up more or less in proportion to the intensity of exposure. This forms a sort of relief map of the negative and is wound on a cylinder over which a stylus traces its path. A microphone attached to the stylus varies the resistance of a local circuit which is coupled to a transmitter. At the receiving station an oscillograph has its mirror deflected, altering the projection of a beam of light focused on a synchronized rotating cylinder having a sensitive photographic film on it. How Jenkins Does It JENKINS' method of analyzing is based on aberration by means of prismatic rings. These rings are of glass, the edges ground in such a manner that a beam of light passing through is given an oscillating motion. By means of two such rings geared at a predetermined ratio, a negative is explored in minute strips, and a photo-electric cell employed to convert light into electrical values. The Bartlane system is a coding process which operates by a printing telegraph. Holes are punched into a tape and reproduced at the receiving end by passing the type in front of a beam of light. Synchronism is