Technikatörténeti szemle 20. (1993)

TANULMÁNYOK - Tihanyi Glass, Katalin: The Iconoscope: Kalman Tihanyi and the Development of Modern Television

influence of light (photoelectric effect) more readily than in the dark. At the transmitting side, the magnetically deflected cathode beam would explore a screen upon which the image was projected through a wire gauze, and transmit the electrical charges — emitted by the photosensitive layer at each successive point the cathode ray touched — to the receiver. Campbell Swinton, however, admitted that this method of transmission and reproduction of the image would only work, provided „all portions of the image were at rest" and added: the somewhat crude form of photoelectric cell described, composed merely of insulated cubes of rubidium in contact with sodium vapor, might be improved upon. Indeed, it is highly probable that research will reveal much more sensitive materials, the use of which would vastly improve this part of the apparatus, which at present is probably the one least likely to give the desired results". Interestingly enough, it has been suggested that the Campbell Swinton proposal anticipated the storage principle. This view, however, is based on the failure or reluctance to recognize that true storage depended on an entirely different mode of operation and several new key elements which, as Campbell Swinton predicted, had to be added to the device he described in his seminal paper. Namely, although one could argue, as has been done, that the individual photosensitive areas of the screen would accumulate and „störe" positive charges, Schröter, Zworykin and others agree that the output would be too small for any practical purpose. The reason for this is the minute capacity of the individual photocells and, as in Campbell Swinton's proposal, the absence of a collecting electrode which would capture the electrons emitted by the photosensitive layer and thus allow continuous accumulation of new positive charges between scansions (23). Thus the minute capacity of the photocells would result in their rapid „Saturation," completed as it were long before the maximum light effect corresponding to the brightest areas of the image could be achieved. It can be established, then, that early electronic television as suggested by Campbell Swinton still depended on scanning, the utilization of photosensitive materials for the image carrier, and the photoelectric effect — that is, the liberation of electrons from certain metals under the influence of light. The replacement, however, of Nipkow's mechanical scanner with the swift and weightless cathode ray and the employment of cathode ray tubes at both the transmitting and the receiving side proved revolutionary advances which endured to our day. The improvements that Campbell Swinton predicted would be necessary to render the image carrier and,