WONDERS OF TELEPHONY

Oamaru Mail, Volume XLIV, Issue 14044, 29 April 1920, Page 7

WONDERS OF TELEPHONY

An instrument- for telephone' communication by means of rays of light, called the photophone, has been invented* (say.i the London correspondent of. the "Sun" and- >Jl\v York ''Herald"), by Professor A. .0. Rankine,.of the London Imperial College. 1 talked with Professor Rankine in a practical test of his invention. The professor utilised electric light beams from an arc light. His words and even his breathing could be heard distinctly at a distance of eight r miles'. Professor Rankine raid that his invention could be used I to produce sound from a motion picture '.film., "One of the chief advantages of my system is the secrecy of the conversations farmed on by means of it." Professor Rankine said." "Although it may be said to be a system of wireless telephony, word* transmitted by it cannot be picked up as in the case of wireless telegraphy, but can be heard only_ by the person addressed and with whom'connection has been obtained. I may add that the only disadvantage which I see in it is that conversation may be carried on. only in a direct line. Practically the 'same experiment which I made was carried on in America twenty years ago, when Alexander GraIham Bell succeeded in speaking over a distance of 22 yards, and then abandoned his expeiintents to develop the telephone. "By his system conversation is carried on through a transmitter, through which light, beams can be mifde to fluctuate according to the vibrations Of the voice. Thus speaking by light rays obviatefi out fide disturbances common to telephone and lo wireless telegraphy and telephony. At the- receiving end light is thrown on a selenium element, which has the property of conducting electricity better when it is illuminated than when it is dark. It is a simple system, and amounts to nothing more or less than connecting a piece oi selenium with an electric battery and a receiving telephone set." Professor Rankine said ho believed his invention would prove most useful to ships at sea. as well as for land communication. "1-ieel confident that in time it will make possible conversation by means of rays of light over hundreds of miles." he said. The apparatus consists essentially of a gramophone sound box with a delicately poised mirror and needle. This needle is actuated in its vibrations by a selenium mirror, which oscillates" according to the fluctuations of' sound coming from the sound box mirror. A travelling receiver conveys these oscillations.

Profes&oi Rankme holds that through this system there is piactically no lim>t. so tai as distance is concerned, to the tian~mi« e ion ol speech Ihe only thing which stands in the wav, he thinks, is the cuL\atme of the earth, since through photophone the light must tiavel m a sfaight line thiough a helio mm or si\ in r he= in diameter.