Technikatörténeti szemle 20. (1993)

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

with it, television a practically viable instrument would be supplied by the concept of ..storage". Zworykin's 1923 patent application While the Zworykin proposal as originally specified in 1923 also featured gas filled tubes, that is, not vacuum technology, it differed from the Campbell Swlnton device in that an insulating layer was added between the photosensitive layer and the conducting back plate. The scanning beam impinged on the back plate; the highly resistant metal insulation would only allow electrons to pass from the photosensitive layer of the screen when and at the point the cathode ray penetrated the back plate and thus established a conductive connection between the two. Consequently, as was the case with the Campbell Swinton proposal but for different reasons, the Zworykin system relied also on the minute local capacity of the individual photoelectric cells. At the time, however — and as the archival documents reveal through the next few years — this arrangement was not seen by Zworykin as a detriment. Ten years later in his 1934 paper, however, with the benefit of hindsight seeing clearly what he had obviously not seen before, Zworykin showed with computations „how microscopic would be the output of the photocell" with such means and under such operational conditions. What Zworykin concealed in this paper was that, as originally filed, his own 1923 application described exactly the type of technology that would yield the result he had just illustrated. As Paul Vajda observed, these early electronic television transmitters and receivers were analogous to mechanical television devices (Nipkow, etc.) in their operation and the resulting charge or current output. For this reason, Vajda, very aptly, characterized them as ..linear" or ..electromechanlcal" systems. Zworykin had characterized these early television system as ..instantaneous" devices, referring to the fact that, as in mechanical systems, they utilized merely the instantaneous charges released by the action of the light on the photocells during the infinitesimally short time the cathode ray impinged upon them as it explored the screen (24). The first demonstration of a television system based on the 1923 Zworykin plans is assumed to have taken place sometime In 1925, while he was still employed by Westinghouse. Various accounts of this event, including Zworykin's own, report that a barely discernible „X" mark was