Radio Broadcast (May 1928-Apr 1929)

NOVEMBER, 1928 WHAT PROSPECTS OF TELEVISION ABROAD 13 BAIRD DEMONSTRATES DAYLIGHT TELEVISION In this picture Jack Buchanan, the popular musical comedy star, is shown sitting in front of the new Baird daylight television camera Mr. Baird is standing in the center, and his assistant is adjusting the lense of the television camera the transmitted current, which, in turn, depended for its variations on the variations of the scanning cathode-ray beam at the transmitter. In these early experiments the use of a selenium cell was depended upon as the link responsible for the actual variations in transmitted current. In 1911' Swinton first suggested the use of photo-electric cells as the basis for the transmitting screen — not a single cell, but a fine mosaic of them — and this idea survives in his latest equipment. Some inventors use the combination of a mechanical arrangement at the transmitting end and the cathode-ray beam at the receiver. Naturally, then, the final result is governed by the speed of the mechanical parts, and the speeding up made possible by the use of electrons throughout is not possible. As a further development, Swinton suggests the use of electrons by means of suitable threeelectrode tubes to supply, from batteries or from the mains, the two a. c. currents of largely different frequencies required to actuate the deflecting magnetic or electrostatic systems at the receiving and transmitting ends, used for the purpose of causing the synchronous, combined oscillating and traversing movements of the beams. The exact synchronization of these latter could be maintained by special radio signals on a wavelength separate from that used for the transmission. Figs. 2 and 3 show the latest Swinton transmitter and receiver circuits, respectively. In these circuits it will be seen that all mechanical motion has been done away with, resulting in circuits hardly more complicated than those used at the present time for broadcasting reception. In describing the operation of his apparatus. Swinton writes as follows: At both ends the two cathode-ray beams impinge on screens, which they are caused by the defecting systems to sweep rhythmically and in complete synchronization in parallel lines backwards and forwards from end to end. In the transmitter the screen is composed of a very large number of minute photo-electric cells each of which are activated more or less by the amount of illumination it receives from the image thrown upon the whole screen by the lens. The end of the transmitting cathode beam explores each of these cells in turn, and as to whether it finds it illuminated and thus activated or not, an electrical impulse of varying intensity, proportional to the amount of local illumination, is transmitted to the neighboring gauze grid. The varying electric current thus originated after amplification and conversion into wireless waves is transmitted to the receiver, where, after further amplification and detection, it varies the strength of the receiver cathode-ray beam, which, in turn affects the brightness of that particular portion of the fluorescent screen on which the end of the cathode beam is at that instant impinging. Thus, on the receiving fluorescent screen a replica of the picture thrown by the lens on the transmitting screen is reproduced. Very probably with modern knowledge and arrangements the transmitting method in which selenium is used might be got to work, though perhaps it would be too sluggish for showing rapid movements in the picture transmitted. A CRITICISM OF MODERN METHODS COMMENTING in a paper on the advances w made in television, whose mechanical devices formed the nucleus of the apparatus, Mr. Swinton has said: — ■ What has been effected mechanically, more especially in America, shows what can be done by vast expenditure, iabor, and elaboration. As experimental shows they were no doubt magni ficent, but having regard to the apparent impossibility of either improving or amplifying to any sufficient extent, one doubts whether they can lead to anything really worth having along their own lines. Surely it would be better policy if those who can afford the time and money would abandon mechanical devices and expend their labors on what appear likely to prove the ultimately more promising methods in which the only moving parts are imponderable electrons. In a letter which appeared in the London Times Mr. Swinton expressed other views on television. Excerpts from the letter follow: To the Editor of the Times: — The telegram on the progress of television in your July 14 issue leads me to think some comment should be made on the many very absurd prognostications that have appeared on this important subject. It is well known that all methods of television are based on the same principle as is the reproduction of pictures in the Press, wherein the picture in each case is composed of a mosaic of minute dots so small and so closely packed together that the individual dots are not recognizable as such by the unaided human eye. Let us take as an illustration a well-reproduced newspaper half-tone 10 x 16 inches in size. This contains more than 250,000 dots. Now on the same principle that requires that cinematograph film pictures have to succeed one another at the rate of 16 a second, so as to give the illusion of continuous motion, for the purpose of successful television each of the thousands of dots has to be registered in its proper place and with its proper strength no fewer than 16 times a second. Thus to transmit the picture referred to would require registering the dots at a rate of 4,000,000 a second. Such achievements are obviously entirely beyond the possible capacity of any mechanism with material moving parts and this view, which I have personally been inculcating in scientific circles for many years, has recently been thoroughly endorsed by no less an authority than Sir Oliver Lodge, himself a notable pioneer inventor in wireless telegraphy, who has recently written two articles on the subject. In these he entirely agrees with my view that nothing of this order can ever be hoped for from material mechanism, and that the only way in which it can ever be accomplished is by doing away entirely with material moving parts and utilizing the vastly superior agency of electrons, those infinitesimal and imponderable unit particles of negative electricity which are the most mobile things known to science. A. A. Campbell Swinton. OTHER EUROPEAN INVENTORS \TOT a great deal is heard of the effort of *■ ^ European inventors on the Continent, although from time to time small items of intelligence do come through. In France, M. Belin, in conjunction with M. Holweck, has succeeded in transmitting shadows. The apparatus of M. Belin is unique in that the transmitter makes use of two mirrors vibrating at right angles to one another, the combined action of which enables the subject transmitted to be explored by a potassium photo-electric cell. At the receiving end there is a fluorescent screen traversed by a cathode ray. Thus we get a combination of the use of the mechanical and the electron! Another Frenchman, M. Dauvillier, has also succeeded in transmitting shadows, but admits that an increase of one thousandfold in sensitivity will be necessary before his apparatus is perfect. Other scientists who are bending their efforts in an endeavor to be first in the race are Mihaly. Korn, Nesper, and Muller. The latter has been experimenting for some time in an endeavor to produce metal foils of extreme thinness, and has produced some of gold a hundred times thinner than heretofore, so thin, in fact, that printed letters can be read through six layers. Varying intensities of light passing through these layers of foil have been found to alter a current of electricity passing through. The use of this discovery may lead to the production of a very cheap television equipment, it is hoped.