Just as is done in radio photographs the picture surface is traversed by a small spot of light moving over the picture surface in successive parallel adjacent lines, with the value of the lines changed by the incoming radio signals to conform to a given order, the order being controlled by the light values of the scene at the distant sending station.
In sending pictures electrically, there have been but two methods employed, perhaps the only methods possible; namely (a) a cylinder mechanism; and (b) a flat surface.
Without exception, every scheme which had attained any degree of success, before the author adopted flat surfaces, has depended upon synchronous rotation of two cylinders, one at the sending station with the picture thereon to be sent; and the other at the receiving station where the picture is to be put.
Perhaps the very obviousness of the cylinder scheme, and that there are no patents to prevent, explains why it has been employed by so many. And there have been many workers in this line of endeavor; for example, in England, Lord Northcliff, Sir Thompson, Mr. Evans and Mr. Baker; in France, MM. Armengaud, Ruhmer, Rignoux, Fournier, and Belin; in Germany, Paul Nipkow, Dr. Anchutz, and Dr. Korn.
In America, Mr. Ballard, Mr. Brown, and Mr. Amstutz, the latter deserving particular mention, for, from a distant picture, a swelled gelatine print, he engraved a printing plate which could be put directly on a printing press for reproduction.
All these many workers have adopted the cylinder method of sending and receiving, and all have arrived at approximately the final stage of development permitted by concurrent science.
It may be well to explain that, in these older schemes, the picture to be sent is wrapped around the cylinder, usually a cylinder of glass where light sensitive cells are employed, mounted on a rotating shaft, which also has longitudinal displacement.
The light values which make up the picture are converted into electric current of corresponding values and put upon a wire or other channel which delivers them to the distant receiving station.
At the receiving station a suitable film-like sheet (paper, for example) is wrapped around a cylinder similar to that at the sending station. As this cylinder is rotated and longitudinally advanced under a stationary point in contact with the paper on the cylinder, a spiral is traced thereon. As the incoming electrical current represents picture values, and as the two cylinders are turning in exact synchronism, a picture duplicate of that at the sending station appears thereon. After the picture is completed the paper sheet can then be taken off the cylinder and flattened out for such use as may be desired.
It is quite obvious that vision by radio and radio movies can never be attained by a cylinder method, for as the picture must appear to the eye complete, by reason of persistence of vision, it naturally follows that the eye must make up the whole picture from a single focal plane.