SEEING THROUGH FOG

Hokitika Guardian, 7 August 1930, Page 2

SEEING THROUGH FOG

TELEVISION FOR FLYERS

A DOUBTFUL STORY. It was recently reported that an American investigator had perfected a “television eye” for aeioplanes which would enable the landing ground to be seen through fog or dense cloud or would allow an aerial observer to see the movements of hostile for es while his plane was hidden behind cloudbanks. Details came to hand of a scheme which purported to be a development of Mr J. L. Baird’s Noctovision apparatus and for which similar claims were made as to the possibility of seeing the landing ground through den-e fog or cloudbanks; but as no hint was given as to how certain very great difficulties were to be overcome publication was withheld until further information could be obtained (writes Captain Ernest H. Robinson, in the London “Observer.”) The clumsily named Noctovision makes use of the fact that it is prssplble to mifinufacitul’Q photo-electric cells that are sensitive to the infrared end of the light spectrum. The photo-electric cell bears the flame relation to television that the microohone does to broadcasting, and just as it is possible to make a microphone that is sensitive to sound waves that the ear cannot-appreciate, so the liaht cell can be made to respond to Halit vibrations which the eve cannot see, Mr Baird’s infra-red apparatus, which was first demonstrated at the Royal Institution in December. 1926. makes a light visible through fog or cloud. It should be noted that a light is necessary; but that the light need not be ordinary light. If necessary, for war operations, it could be of infra-red rays only, and would he completely invisible to anyone not having the necessary apparatus sensitive to those rays. In its present form it can he used by ships or planes. The step from the use of a light, either on the landing-ground, or on the aeroplane itself,; to enable the. television eye to work, is so enormous that these reports must be received with the greatest caution. • To, see a landingground through fog from a plane in the air| necessitated either the flooding of the ground with infra-red rays or the use of a photo-electric cell so sensitive as to be an enormous and unthinkable advance on anything that has yet been done. In the circumstances it- is more than probable that this American device is simply the Baird Noctovision apparatus, or something very like it. It was just in the details of the actual amount that could he seen, and the type of photo-electric cell to be used, that the information which came from America was lacking. Progress in matters scientific does not usually progress by enormous leaps. Details of the work of investigators all over the world are known to other investigators and to interested persons, and the knowledge that certain developments are possible and may be shortly looked for, is usually well in advance of performance. So far as is known, though the photo-electric cell is gaining in sensitivity through the constant work of physicists, it has not yet reached the stage when an object a long way off and enveloped in fog or screened by cloud can be seen, by reason of the infra-red sensitivity of the cell. Its actual development has only so far advanced that television by ordinary daylight can be obtained. The actual apparatus necessary for a “television eye,” such, as has been claimed to have been invented, is some f- rm of telescope arrangement to make details of distant objects visible. This, in itself, leads to a loss of light to some extent. Then a photo-electric cell sensitive to the infra-red rays, a scanning disc revolving before some kind of light source, and at least one amplifier making use of thermionic valves. The weak link in the chain is the light cell, which, as has been said, must he so enormous’y sensitive to the infra-red rays as to be beyond present possibilities.