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8
National Board Review Magazine
Delegates arriving at one of the Conference Sessions
electronic methods of pick-up and viewing.
Campbell Swinton conceived the idea of a mosaic screen of photo-electric elements which were to form a part of a special cathode ray tube. The image of the screen to be transmitted was to be projected on to the mosaic screen by means of a lens, and the back of the screen was to be scanned by a beam of cathode rays controlled magnetically by the currents from two alternating current generators. The cathode ray beam in the receiver was synchronized with tlaat in the transmitter by means of deflecting eoils connected by wires to the same generators as the transmitter, and a separate conductor carried the photo-electric currents for modulating the receiver beam.
In 1911 the three electrode amplifying tube of Lee DeForrest was practically unIcnown and hence this system was never tried. Our present television is only possible with the addition of this vastly important invention.
And so we jump to 1925 when Jenkins
in America and Baird in England, witliin a few months of each other, actually succeeded for the first time in transmitting crude pictures from a transmitter to a near1)3' receiver. Each had utilized many of ihe contributions previously enumerated which were essential for successful operation, and neither had added any basic new feature to make this possible.
From this time progress was more rapid, and although the bulk of the work done was on mechanical systems definite improvement was shown. Many scanning systems were tried utilizing devices such as the Nipkow disc, mirror disc, lens disc, mirror drum, lens drum, mirror screw, vibrating mirror, rocking prism, sliding prism, prism rings and many others.
In spite of all this, in 1931 the picture being transmitted consisted of only 60 lines at a speed of 20 pictures per second, which was entirely inadequate as regards detail and flicker. Furthermore, the defects of the mechanical systems had been made only