The talkies (1930)

54 THE TALKIES The photo-electric cells are absolutely instantaneous in responding to the fluctuations of light up to enormous speeds, and are perfectly capable of handling the upper limit of 10,000 vibrations per second which the Talkie engineers are aiming at. It is interesting to notice how closely allied these photo-electric cells are to the wireless valves of the present day which actually have made their use possible. It has been known for many years that if certain kinds of light illuminated the plates of certain metals, the spaces round these plates were charged with negative electricity. In 1883, Edison, in America, and Professor Fleming, who was electrical adviser to the Edison Electric Light Company in London, were puzzling over certain problems in connection with the manufacture of electric-light bulbs. Both inventors noticed that as the carbon filament lamps of that day grew old, their light was greatly diminished by the formation of a dark cloud on the inside of the glass. Some readers may remember this trouble. Edison and Fleming were particularly puzzled by the fact that especially in burnt-out lamps there were patches of comparatively clear glass. A series of experi