TALKING OVER LIGHT BEAM

Hawera Star, Volume LII, 28 January 1933, Page 11

TALKING OVER LIGHT BEAM

(SCIENTISTS of Schenectady, New York, have talked over a light beam 24 miles long, states the New; York correspondent of the "(Morning Post," with another group of scientists at Lake Desolation across the Lower Adirondack Mountains, This achievement is the sequel to similar experiments conducted in secret for the Admiralty during the war by the British scientist Professor A. O. Rankine. 'ln the opinion of Professor Rankine, expressed in an interview, the method may lead to a valuable means of secret communication. He suggests that there is no reason why the same method should not be applied to infrared or invisible light rays.

The method is described in America ■by the present experimenter, Mr John Bellamy Taylor, as "narrowcasting." The name is derived from the fact that communication is confined to a narrow' beam of light in place of the spreading associated with ordinary wireless communication. In the present experiments a searchlight mounted on top of fho General Electric building in ‘Schenectady projected a beam on to a 30in. mirror w T hich was part of the Lake Desolation receiving apparatus. To the Adirondacks party tne searchlight appeared like a distant twinklng star. Mr Taylor’s voice came across the beam somewhat distorted, but was frequently heard clearly. The longest distance over which communication had previously been established in this way in America was last year, when the Schenectady laboratory talked with the naval dirigible Los Angeles two miles away.

Voices Heard for Twenty r Four Miles

In 1917, however, Professor Rankine j was able to talk over a distance of between two and three miles, and when the ban of secrecy was lifted after the . war his results were published by the ! Physical Society of London. "I am not- at all surprised at the present imI provement, ’’ Professor Rankino said, "which would be sufficiently accounted for by the improvement in amplification and in the photo-electric cells which would b eused at the receiving station. In my experiments the vibration of speech was imparted to the light beam through two grids. When the transmitting mirror was stationary the two grids were in alignment and part of the beam of light passed through them. If, however, vibrations from the microphone were allowed to move the mirror through a small distance, the alignment was disturbed and the light was partially or completely eut off. "The method was rejected by the Admiralty in favour of wireless, on the ground that the light beam would be ooscured by the smoke of battle. There seems to be no reason why the method should not be applied to invisible in-fra-red rays, and I cannot imagine that a photo-electric cell could not be developed which was sufficiently sensitive to them. There would then be available a uni-directional and secret method of communication with no theoretical limit but the curvature of the earth. And the rays would be capable of penetrating fog and mist." From 19.17 to 1918 Professor Rankine was chief research assistant of the Admiralty Experimental Station f at Harwich. i