WONDERS OF TELEPHONY.

Manawatu Herald, Volume XLII, Issue 2127, 13 May 1920, Page 4

WONDERS OF TELEPHONY.

BEAMS FROM AN ARC LIGHT USED. CAN TALK IN SECRET. An instrument for telephone communication by means of rays of light, (‘ailed the photophone, has been invented (says the London correspondent of the Sun and New York Herald), by Professor A. 0. Rankine, of the London Imperial College. I 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 miles. Professor Raukine said that his invention could be used to produce sound from a motion picture Him. ■‘One of the chief advantage- of my system is the secrecy of the conversations carried, on by means of il/' Professor Rankine said, “Although it may be said to be a system vf circles s telephony, words traitsrfi

mitted by it cannot be| picked up as in the ease 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 he carried on only in a direct line. Practically the same experiment which I made was carried on in America twenty years ago, when Alexander Graham Bell succeeded in speaking over a distance of 22 yards, and then abandoned his experiments to develop the telephone.

“By this system conversation is carried on through a transmitter, through which light beams can he made to fluctuate according to the vibrations of the voice. Thus spm liking by light rays obviates outside disturbances common to telephone and to wireless telegraphy and telephony. At the receiving end light is thrown on a selenium element, which has the property of conducting electricity holler when it is illuminated than when it is dark. It is a simple system, and amounts to nothing more or hiss than connecting a piece of selenium with an electric battery and a receiving telephone set.”

Professor Rankine said he believed his invention would prove most useful to ships at sea, as well as for land communication. “I feel confident that in lime it will make possible conversation by means of rays of light over hundreds of miles,’ 1 he said. Thd apparatus consists essentially of a gramaphone 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 coining from the sound box mirror. A (ravelling receiver conveys these oscillations. ' Professor Rankine holds that through this system there is practically no limit, so far as distance is concerned, to the transmission of speech. The only thing Avhieli stands in the way, he thinks, is the curvature of the earth, since through the pholophone (he light must travel in a straight line through a helio mirror six inches in diameter.