THE TALKING FILM

Taranaki Daily News, 24 November 1926, Page 10

THE TALKING FILM

AN ELECTRIC EYE. SEE CANDLE BURNING MILES AWAY. T. Thorne Baker, F.lnst.P., F.R.P.S., writes in the London Daily Mail:— We are going to see a good deal of the talking film before long, and we are so used to hearing things by wireless and listening to exquisite reproductions of music on the gramophone that the marvel of the talking film does not perhaps strike one as it deserves. Long before the war inventors had succeeded in photographing speech on a kinematograph between an electric lamp and a selenium cell had made the cell reproduce in a telephone the original voice. But, like many another invention, it reached an impasse, and had to wait for many years until the wanted link in the chain was provided by a further discovery. The stepping stone to success lias been provided by the “electric eye”— the little bit of apparatus that technical people term a photo-electric cell. It consists of a deposit of potassium, or some such metal, on the inside of a vacuum tube, with a plate or metal ring to act as a collector. 1,000,000 th OF A SECOND. When a ray of light falls on the potassium electrons are liberated and fly across to the collector, providing a path for an electric current. The currents dealt with are excessively small and require great amplification by means of valves. But the photo-electric cell gives us currents corresponding exactly in strength to the strength of the light falling upon it. It responds to a change in the light strength in a millionth of a second, and will “see” the light of a caudle burning 21 miles away! In making a record, the microphone is used in the ordinary way. Its currents are amplified by valves and are then made to control the strength of a special type of electric lamp. The light from this lamp thus fluctuates exactly in accordance with the voice or sounds caught up by the microphone. This light passes through a fine slit and falls upon a travelling photographic film. The film is developed, and from the negative any number of positive pictures of the sounds can be made. LOUD SPEAKERS. The film is made to talk by passing the light from a small incandescent lamp through it, and letting the rays so controlled by the film fall upon one of these remarkably sensitive photo-electric cells. The fluctuating beam of light varies the current in the cell—currents of the order of a millionth of an ampere. These currents are then amplified by valves and passed into a loud speaker. The photo-electric cell used by Dr Lee de Forest is an unusual one, which has been specially designed for the work by Mr. T. W. Case. It is really the photo-electric cell which has won the battle for the inventors of talking films, coupled with the incredibly useful invention, the three electrode valve.