The Electric Eye

Radio Record, Volume III, Issue 41, 24 April 1930, Page 2

The Electric Eye

ALMOST every month we read of some new task set to that wonderful little glass bulb the electric eye, which can turn a ray of light into an electric current. The strength of the current is always in exact proportion to the strength of the light, and, as electric currents can be accurately measured, it has been found easy to measure very feeble beams of light with the help of the electric eye (known to scientists as a photo-electric cell). a A big paper mill has just the exact weight of the paper P factured can be measured by light. A bear: of light is thrown through the paper while it is running along the machine, and some of the light, of course, passes through the paper. The light passing through falls upon a photo cell, and its strength is recorded on a measuring instrument. If the paper is too thick too little light will reach the photo cell; if the paper is too thin too much light will pass through. The slightest variation in thickness of the paper is thus recorded, and the mill can keep the weight of its paper within the finest limits. of