AN ELECTRIC EYE

Evening Post, Volume CVII, Issue 73, 30 March 1929, Page 15

AN ELECTRIC EYE

An electric eye, which is a pet name for what is less happily called the photo-electric cell, misses very little. One that was installed at the Optical Society's Exhibition at the Imperial College of Science counted the passersby. Another could see a burglar, though the burglar would never see the electric eye's gleam turned on him. Another was so sensitive that it could catch sight of dust or smoke in the air as easily as the human eye can perceive the motes in a sunbeam. In each case the photo-electric cell was electrically imitating the action of the human eye. When light falls on the retina a message is telegraphed to the brain. When light falls on the photo-electric cell an electric current is sent along a wire to a battery. The people were counted because each time a person passed the turnstile he cut across a beam of light which was falling on an electric eye. The burglar also crosses a beam of light, but in this., case it is invisible light (or i:;-,:it which, thougl) invisible to t!i" l.i.uian eye, is visible.to the electric eye). What happens is that the particles of dust or smoko in the aid have a light ray thrown on. them. They reflect it to the electric eye, which sees them as the human eye sees them on a brighter scale when a beam of strong sunlight falls among them.