Seven-League Camera

In a Manhattan skyscraper on lower Broadway, an engineer pulled a switch. Simultaneously two cylinders began to turn, one in New York, and one in the Discount Building, Cleveland. Two hundred and seventy-six seconds later a photographic film of President and Mrs. Coolidge, the original of which was 600 miles away, was ready for development in Manhattan. This was the first public demonstration by the American Telephone and Telegraph Co. (see Page 21) of the most successful method of electrically transmitting photographs yet developed. It is by no means the first time the feat has been done, however. The best-known previous method is probably that of Edouard Belin (TIME, April 7, 1923), who, on Nov. 14, 1920, transmitted photographs from St. Louis to New York. The New York World owns the American rights of the Belin system, which it has improved in private research, but has not yet used commercially. The Belin principle is quite different from the A. T. & T. process. The photo graph becomes a relief map, the elevations and depressions causing the variations in the electrical current, instead of a beam of light. The Radio Corporation of America owns the Alexanderson method (TIME, Nov. 12), very similar to the Telephone method, by which photographs have been transmitted from New York to Poland and back again. C. Francis Jenkins, a Washington inventor (TIME, June 25), has also transmitted photographs at a distance by radio, instead of by telephone wires, and has even sent simple motion pictures by radio within a building. The A. T. & T. engineers say, however, that the possibility of transmitting action pictures of ball games, riots, prizefights, parades, etc., directly is almost negligible. Fifteen photographs in all were transmitted from Cleveland to New York on the first day of the test -- all within two hours. The actual time of transmission for a 5x7 picture was only 4 1/2 minutes. There were several portraits, including a group of three men in the Cleveland office. This picture was taken by flashlight (owing to a cloudy day) at 3:59 p. m. The film was developed, a positive print made, and it was "put on the wire." In 44 minutes from the time the flash was snapped, a fully developed negative of it was available in New York. There were also several pictures of street scenes, buildings and bridges in Cleveland, which were reproduced with fair distinctness. The New York newspapers, contrary to their usual custom, did not retouch the prints, so that the cuts were somewhat inferior to ordinary newspaper halftones.

The process, in brief, is as follows: The photographic film (it can be used wet, direct from the developing bath) is held taut and curved in the form of a cylinder, like an old-fashioned phonograph record. Light, from an ordinary automobile lamp, is passed through a lens and concentrated in a small spot at one corner of the film. At the receiving station a blank film is formed into a similar cylinder. By a device known as a synchronizer, the cylinders at both ends are started simultaneously and turned at the same rate of speed. The light beam travels in a continuous line over the picture, until it reaches the opposite side. In the center of the cylinder is a "photoelectric cell," consisting of a rod of potassium in a vacuum tube. It is so sensitive to light that any ray falling on it causes the electrons to fly from its surface, generating an electric current. As the cylinder revolves, the point of light passes through the transparent film and falls upon the potassium. In the dark parts of the picture less light gets through, and in the light parts, more. The current initiated by the photo-electric cell varies in strength exactly as the intensity of the light that reaches it. The fluctuations of the current are shunted onto the telephone wire and added to the uniform direct current. This is billions of times as powerful as the original current, but it carries the variations in the same proportions. The current is then carried over the long-distance telephone wires. At certain relay stations (Pittsburgh and Philadelphia in this case), the current is "stepped up" by vacuum tubes to make up for any loss in transmission.

At the New York end the receiving apparatus consists of an electric lamp behind a thin metal wall, placed in a strong magnetic field. The wall forms one side of a narrow slot through which the light passes. The fluctuations in the current passing through the magnetic field move the metal wall back and forth according to their intensity, making the slot wider or narrower. The light beam, passing through the slot, falls on the revolving cylinder, printing broader or narrower lines of light on the film. With each revolution the cylinder is jerked 1/65th of an inch to the right, and the spot traces another line exactly parallel. This interval was found the best for newspaper pictures, but the machine can be set for any degree of fineness or coarseness, according to the type of engraving to be reproduced.

The present process is not a new invention in itself, but a combination of a series of inventions, refined and perfected by the Telephone Company's engineers. No one man is especially responsible, and the Company prefers not to apportion credit, but to keep it anonymous. The experimental work was started only about a year ago, with the definite aim of producing a commercially feasible process of picture transmission.

The sending apparatus was installed at Cleveland in order to transmit pictures of the Republican National Convention this month.