Vision by Radio
C. FRANCIS JENKINS
The earliest attempts to send pictures and to see electrically date back some fifty years, being practically coincident with efforts to transmit sound electrically.
At first a metallic circuit was employed to carry the impulses representing picture values, but when radio was available several workers immediately began the adaptation of their apparatus to radio circuits.
Some remarkably fine examples of pictures transmitted by both wire and radio have been produced in recent months; most of them showing the lines, but some of them without lines at all, i. e., true photographic results.
And as the transmission of images from living subjects in action differs from “still” pictures only in that they are more rapidly formed, it naturally followed that the solution of this problem should also be undertaken.
When radio service to the eye shall have a comparable development with radio service to the ear, a new era will indeed have been ushered in, when distance will no longer prevent our seeing our friend as easily as we hear him.
Our President may then look on the face of the King of England as he talks with him; or upon the countenance of the President of France when exchanging assurances of mutual esteem.
The general staff of our Navy and Army may see at headquarters all that a lens looks upon as it is carried aloft in a scouting airplane over battle front or fleet maneuvers.
And from our easy chairs by the fireside, we stay-at-homes can watch the earth below as a great ship, like the Shenandoah, carries our flag and a broadcasting lens, over the mountains and plains, the cities and farms, the lakes and forests, of our wonderful country.
In due course, then, folks in California and in Maine, and all the way between, will be able to see the inaugural ceremonies of their President, in Washington; the Army and Navy football games at Franklin Field, Philadelphia; and the struggle for supremacy in our national sport, baseball.
The new machine will come to the fireside as a fascinating teacher and entertainer, without language, literacy, or age limitation; a visitor to the old homestead with photoplays, the opera, and a direct vision of world activities, without the hindrance of muddy roads or snow blockades, making farm life still more attractive to the clever country-bred boys and girls.
Already audible radio is rapidly changing our social order; those who may now listen to a great man or woman are numbered in the millions. Our President recently talked to practically the whole citizenship of the United States at the same time.
When to this audible radio we add visible radio, we may both hear and see great events; inaugural ceremonies, a football, polo, or baseball game; a regatta, mardi gras, flower festival, or baby parade; and an entire opera in both action and music.
Educationally, the extension worker in our great universities may then illustrate his lecture, for the distant student can see as well as hear him by radio.
It is not a visionary, or even a very difficult thing to do; speech and music are carried by radio, and sight can just as easily be so carried.
To get music by radio, a microphone converts sound into electrical modulation, which, carried by radio to distant places, is then changed back into sound and we hear the music.
To get pictures by radio, a sensitive cell converts light into electrical current, and at radio distances changes these currents back into light values, and one may see the distant scene; for light is the thing of which pictures are made, as music is made of sound.
To further show the close relation, it might be added that in receiving sets these same electrical values can be put back either into sound with headphones or into light with a radio camera; although it may be admitted that such radio signals do not make much sense when with headphones one listens to the pictures.
Already radio vision is a laboratory demonstration, and while it is not yet finished and ready for general public introduction, it soon will be, for it should be borne in mind that animated pictures differ from still pictures only in the speed of presentation, and the sending of “still” pictures by radio is now an accomplished fact, radio photographs of no mean quality, examples of which appear as illustrations in this volume.
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.
The attainment of “television” or Radio Vision, as it is now coming more commonly to be called, requires that the sending shall be from a flat plane, and reception on a flat plane, and a modulation which will give not only the high-lights and shadows but the halftones as well.
These “flat planes” may, of course, be the focal planes of the lenses employed at the receiving station, and from the focal depth of the lens at the sending station where the picture may perhaps be taken from living actors in the studio or from an outdoor scene.
At the receiving station the “flat surface” may be a photographic plate, a white wall, or a miniature of the usual “silver sheet” of the motion picture theatre.
It may aid in a clearer and quicker understanding of the text if the words telephone and television be limited to metallic circuit service, while radio phone and radio vision is applied to radio carried signals, and this designation will be employed in the following pages.
This and succeeding pages are examples of photographs received by radio from a distance, by the Jenkins system, some of them from Washington to Philadelphia, and represent the best work done in 1922, 1923, and 1924.
