Infra-Red

In the wide spectrum of electromagnetic waves--from the very short, very rapid cosmic rays (.000,000,000,004 cm.)* to the comparatively long, slow radio waves (2,500,000 cm.)/-only a small section is perceptible to unaided human senses. That section contains light rays and heat rays, and the intermediate infra-red rays which are neither light nor heat, yet are of the nature of both. Scientists are gradually learning how to put the infra-red rays to work. Doctors use them to create artificial fevers. Practical physicists used them otherwise last week.

In the auditorium of the Eastman Kodak Research Laboratories at Rochester, N. Y. four dozen industrialists and research engineers sat in pitch blackness. They were on tour of various industrial research laboratories and had stopped at George Eastman's kodak plant for Dr. Charles Edward Kenneth Mees to take their pictures in the dark. The room they posed in was flooded with infra-red light from an airtight, light-tight cabinet. A camera was loaded with a proper plate. The camera clicked a one-second exposure. The lights went on. While the businessmen blinked their eyes and chatted, photographers developed the plate, made prints. Fifteen minutes later the businessmen could see themselves as no man had ever seen them, the way they looked in the dark. Practical uses of the infra-red camera might be to photograph burglars or other wild animals.

Another demonstration of infra-red use occurred last week on the roof of England's Croydon Airdrome control tower. There Paul Humphrey MacNeil of Huntington, L. I. showed his infra-red sextant. Navigators locate their position at sea or in the air by determining how high the sun is above the horizon. They "shoot the sun" through the eyepiece of a sextant. If the day is cloudy, they cannot see the sun, although they may know its approximate location. The MacNeil sextant is connected with an amplifier sensitive to the sun's infra-red rays. Those rays go through clouds. All an uncertain navigator need do is to sweep the sun-obscuring cloud with the eyepiece of this special sextant until the amplifier gives the greatest response to the sun's invisible presence.

*Written more briefly, 4x10 -12 /-More briefly, 2.5x10 6 cm.

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