TELEVISION PROSPECTS

Evening Star, Issue 19020, 15 August 1925, Page 9

TELEVISION PROSPECTS

SOME REGENT EXPERIMENTS An apparent similarity between the, processes of sight and hearing, based upon the fact that both involve a form of wave energy, encourages the belief that wireless telephony will shortly be followed by the discovery of a successful system for transmitting scenic effects by the same medium (says a correspondent to the London ■.cimes’). A wireless equipment capable of reproducing simultaneously nob only the roar of .Niagara, but also a “ moving picture ” of the falling waters, undoubtedly opens up a fascinating prospect to the radio enthusiast. Unfortunately the two. problems are very widely separated in practice, and although some progress has been made in the direction of television, success is still far from being realised. The ordinary kinematographio effect of motion depends upon what is termed the persistence of vision. The eye, in fact, refuses to recognise the interval between successive “ still life ” pictures, provided these follow each other at a rate of from ton to fourteen per second. In such circumstances the effect produced upon the observer is that of a smooth continuous movement without any perceptible _ hiatus. If the kinomatographic principle is to be utilised in wireless television it follows that complete pictures of the distant scene must bo transmitted through the ether at the rate of at least ten per second. The apparatus employed must also be capable of maintaining this snood indefmitcdy without hitch or failure.

i Tho transference of written signatures and even of photographs suitable for subsequent reproduction by process printing, has already been successfully accomplished by Ivf. Edouard Bolin and others by tcle--1 grapliy over a lino wire, but the time reI q aired varies from live to twenty minutes I for each complete transmission. Tho operation involves a special preparation of each photograph and tho subsequent traversal of its entire surface in successive strips by a : stylus. Tho stylus records the position of , each grain going to form tho resultant light i and shade effects, by sending a corresponding electric impulse to the line. These are received at the distant station by a similar apparatus, accurately synchronised with •tiiio iirsb and arranged to reproduce each grain in turn, and so build up the picture , piecemeal. ; Tho difficulty of adapting such a method I to radio transmission, while at tho same I time increasing tho speed of operation to the degree necessary to produce a kinernatographic effect, lias so far proved insuperable. A somewhat similar process to that described has, however, been successfully used to transmit photographs across the Atlantic by wireless, but the time taken was in fact considerably longer than that required by the known telegraphic method, owing to the increased difficulty of synchronising the transmitting and recording apparatus whore high-frequency carrier-waves are concerned.

Among recent developments of promise mention may bo made of a special system of prismatic lenses for causing a beam of light to traverse each portion of the picture in rapid succession. 'I ho ell eels of variations in light ami slrdf are conveyed ! v tho light-day to a selenium cell or oifidr optically-scusiiive device, and so transit.oil into corresponding current fluctuations, which aro then utilised to modulate tho carrier-wave. This admits of a very considerable speeding-up of tho process of transmission, and it is claimed that true moving picture effects have been secured in America bv ita use.

Experiments have also been made in this country with a. system in which the liybt and shade effects of a visible object have been translated by stroboscopic apparatus and a selenium cell into a correspondin'} medley of audible frequencies, which are then radiated. A bank of highly-sensilive resonators at tho receiving station analyses the sound medley into its component parte, and reassembles them as light and shade effects in their original aspect. The merit of this method lies in the fact that no mechanical synchronisation is required between tho sending and receiving apparatus. Tho received image varies in appearance simultaneously with tho object, without depending upon any kinematographic or persistence or vision effect. Up to the present, however, this system has not emerged from the purely experimental stage.