DETECTING THE ENEMY

Manawatu Times, Volume 61, Issue 12, 15 January 1936, Page 13

DETECTING THE ENEMY

Do you know that the heat from a candle 50 miles away can be detected? It sounds like a stunt, but military experts are applying its basic principles in apparatus designed to reveal the location of enemy aeroplanes or battleships. By employing the most sensitive galvanometer and amplifying unit available or by concentrating the heat rays with a huge lens or concave mirror focussed on a photo-electric cell, the scientist “linds” the distant candle, in the same way the military man may pick up the heat rays from the motors and exhausts of air or sea craft, plot the exact location and train anti-air-craft or shore batteries on the approaching ships long before they are within range. ’These heat rays, also known as infrared rays, travel at the speed of light, about 185,000 miles per second, but are invisible. Since sound waves move at only 1080 feet per second, heat rays can be detected many miles before the sound of the plane or ship can be picked up by the most sensitive detector. Equipment probably similar to the candle detector has been tested in secret by the U.S. army, with unusual results. Some type of range-finding apparatus was used to locate “enemy” vessels far at sea in the darkness and

Invisible Rays Effective

to enable “gunners” to score direct “hits’’ with powerful searchlights. A New Jersey laboratory is known to have produced gigantic searchlight reflectors, with 60-inch concave metal mirrors so near perfect they require no machining or polishing, liiiodium, a metal more expensive than gold, is used for the reflecting surfaces because it is practically immune to atmospheric corrosion and to the terrific heat of searchlights. Rhodium has high reflection characteristics over a wider colour rajige than other materials, reflecting all light waves, from ultra-violet through the visible spectrum and including the invisible infrared or beat ray. <Bo it is possible that rhodium bearchlight reflectors were .used to concentrate heat rays from-"enemy” ships on the photo-electric cell, enabling rangetinding crews to fix the location with their instruments. It also is possible that rhodium reflectors were used to direct the invisible rays against the distant ships, then to pick up the ray* when they bounced back. Commander P. MaeNcil, an English inventor, has devised simple, detector* that are remarkably sensitive to heat rays from ships and planes. Operation is almost as instantaneous h# direct sight, even in dense fog or in darkness.