Art. 5.-THE BEGINNINGS OF TELEVISION.

WHEN the face of a young man in New York has been seen at the same time in three homes, streets apart, the question Can Television Come?' seems to have been answered. The machine that will transmit face images which appear without a flicker and are so clear that the blink of an eyelid can be seen, must be, one would think, as near to the perfect television machine as the crude instrument into which Graham Bell in 1876 said, Mr Watson, come here, I want you,' was near to-day's telephone. Bell had discovered the true principle of sound transmission, and his apparatus needed only refinement. It is a question whether the men who are now demonstrating television have hit upon the true principle of sight transmission.

It was the discovery, more than sixty years ago, that the metal selenium altered its resistance to electricity when light was shown upon it that set men's minds thinking of sending sight over a distance. It was seen that this property would enable light to be changed into electricity, and if this method had proved to be as direct as Bell's, of changing sound to electricity, we might easily have had television before the telephone came. Since the earliest days, and until now, investigators have taken it for granted that changing light into electricity is the one possible method of achieving television. The telephone imitates the ear, and the first effort at television was an attempt to imitate the eye. A man called Carey published details of an instrument after this fashion in 1880, and twenty-five years later Prof. Ernst Rühmer, of Berlin, transmitted simple figures by television with a bank of selenium cells.

When the eye sees, an image is focussed on the retina from which innumerable nerves lead to the brain. To imitate this mechanism Rühmer had a mosaic of selenium cells with wires leading away from each. It would be a hopeless task, however, to attempt to try to mass together enough selenium cells to have leading away as many wires as there are nerves coming from the retina. Another fact that makes an imitation of the eye undesirable, though the same fact makes possible present forms of apparatus, is that the retina can retain an image for a fifteenth

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of a second. This is achieved by the 'visual purple,' and experimenters have taken this substance from a beast's eye, and even from a human eye, to use it-without permanent success-in their experiments. Although help has been afforded by its study, the realisation has 8T been forced on experimenters that it is useless to take the eye as a strict model. In April 1927, the American Telephone and Telegraph Company during their New York-Washington television demonstration used a fourfoot screen with 2500 wires leading from it; but they realised that this was but a costly experiment which could lead to little valuable practical application.

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It was not only the unapproachable construction of the eye which held back the early investigators from realising brilliant results. Selenium certainly varied a flow of electric current according to the strength of light being shown on it; but it did not respond nearly quickly enough, and when it had responded it was slow to withdraw its effect. It was like a mob, difficult to stir into revolt and equally difficult to calm again. Selenium held out the promise, but withheld the fulfilment. While it was spoiling hopes, however, the principles were being discovered which led to the present photo-electric cell, a device akin to the wireless valve, that, depending on the flow of electrons which have almost no weight and can travel at any speed, gives an instantaneous response as nearly as can be imagined.

With the efficient photo-electric cell as an electric eye, investigators have continued with their attempts to achieve television by turning light into electrons. When you show no light to a photo-electric cell connected in a circuit, no current passes; when you show a dim light to the cell, a weak current passes; and when you show a strong light to the cell, a correspondingly strong current passes. If, however, you pointed a photo-electric cell to the scene you wished to transmit, just as you would point a camera lens if you wished to photograph the scene, you would have given out simply an electric current corresponding to the total amount of light in the scene. What must be done, then, is to take part by part of the scene, in order, show them to the photo-electric cell, and then at the receiving

end take the series of currents received, change them back to light, and arrange these patches of light and shade into a picture of the scene.

One of the simplest ways to do this, it has been found, is to have a large disc with holes near the edge arranged in the form of the first coil of a wide spiral. The suggestion was first made by Plotnow, in 1884. An arc light shines from behind, and when the disc is set spinning beams of light from the successive holes cover the face of any one standing before the disc, a strip at a time. As each part of the face is illuminated the light reflected-little if dark hair is being encountered, and much if the light is striking, say, on the forehead-is caught by photo-electric cells placed in a frame surrounding the disc, and correspondingly strong or weak currents are sent out. The currents are transformed into wireless waves which are collected by a wireless set attached to the receiving apparatus and converted again into varying currents which send a lamp rapidly in and out. A disc similar to that at the transmitter spins before the lamp exactly in time with the other disc, and strips of light and shade are flashed over a screen to build up the picture of the face before the transmitter.

This was the principle of the apparatus used by the American Telephone and Telegraph Company in 1927 when they gave a demonstration so successful that people in New York could see Mr Herbert Hoover, the Secretary of Commerce, who was 200 miles away in Washington, turning over his papers. One receiver had a disc like that at the transmitter, and gave a picture two and a quarter inches square, and the other was the grid of neon tube I have mentioned, four feet square, with 2500 electrodes forming glowing patches of the picture. In this apparatus were many elaborate devices, arranged by two hundred engineers and scientists. By cutting out some of these elaborations, especially those established to ensure the synchronous spinning of the discs at each end, the General Electric Company constructed machines by which they were able early in this year to broadcast television and receive the images in three New York homes.

Mr John L. Baird, who has for some years been

experimenting in television in Great Britain, has based all his forms of apparatus on discs. In the early apparatus used to demonstrate television to members of the Royal Institution-the machine which is now in the Science Museum at South Kensington-Mr Baird had three discs in order to perform successive divisions of the object to be transmitted. The machine used this year to send faces across the Atlantic was, Mr Baird tells me, a development of this apparatus. I have toured the Continent to meet the leading television investigators there, and I have found that they do not rely on the disc to bring the scene to be transmitted before the photo-electric cell. Herr Dénes von Mihály, in Berlin, and M. Edouard Bélin, in Paris, use small rapidly oscillating mirrors. The mirrors are made to move so that they 'see' each part of the image in turn and reflect it to a photo-electric cell.

In these systems, however, as in those of Great Britain and America, the investigators are attempting to achieve the necessary speed by mechanism. It is computed that 30,000 patches of light and shade are necessary to make a recognisable picture, and since the image on a television screen has to be repeated at least ten times a second to give continuity and movement, this means that 300,000 units of light and shade must be dealt with every second. It needs no deep acquaintance with mechanics to know that the achievement of such a speed with our stolid materials of wood, glass, and steel would be difficult. This speed is not enough to fulfil for us the popular promises of watching at home the boat-race, horse-races, and other motley scenes. Sceptics say the speed necessary cannot be approached.

Whenever anything new is proposed there are plenty of people who oppose it; people whose knowledge gives weight to what they say. How many scientists in the world's history have missed success through maintaining their faith in Aristotle's dogmatic guesses? Priestley and Scheele, whose simultaneous discovery of oxygen broke down the old theories of combustion, held in spite of their own new knowledge a blind adherence to the theory of phlogiston to the end of their lives. In television, however, although there are the usual number

who say from principle that such an assault on Nature as seeing across the world can never come, there are men with real and weighty arguments which cause even optimistic people like myself to pause. When I was in Vienna last year I was given six printed sheets, with intricate formulæ as illustrations, setting out a long lecture delivered by Prof. F. Aigner trying to show that television with our mechanical means can never come. Three times now, with three separate mechanical television systems successfully demonstrated, Prof. Aigner has been shown to be not completely right. Yet we do not know that the spinning discs which have produced a face without a flicker can produce scenes. Apart from the speed necessary the accuracy demanded is almost terrifying to a practical man. It is such that the almost imperceptible wear caused by a short spinning of the disc is enough to throw the disc out of place and spoil the picture. An actual television worker who believes mechanism is too slow and clumsy to redeem television's promises is Prof. Max Dieckmann, who told me, when I met him at his laboratory near Munich, that he had scrapped the mirror transmitter which had enabled him to transmit shadows of objects. He is impressed now with the possibilities of electrons.

Now electrons seem ideal for television. They are particles of electricity which, set free in streams, can travel almost as fast as light. They are so light that some scientists believe they have no weight. Years ago scientists used streams of electrons in a cathode ray oscillograph. This you can imagine as a wide tube from which the air has been exhausted. A stream of electrons is set free at one end, the stream is bent back and forth by two electro-magnets placed halfway up the tube, and then it strikes a screen at the other end of the tube which is so prepared that a tiny splash of light appears as each electron hits it. Television workers have made use of the oscillograph for their receivers. Prof. Dieckmann uses one, and the receiver to M. Bélin's apparatus, constructed by M. Holweck of the Radium Institute, also is a cathode ray oscillograph. For television the magnets are so operated that they draw the fine stream of electrons over the screen exactly in time with the zig-zagging beam of light at the transmitter. The vary