Word: infra
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...After bending a beam of sunlight through a prism, he found that a thermometer heated up most if it was placed just beyond the red end of the spectrum. Herschel concluded that the mysterious heat source was invisible rays from the sun, but he could hardly have known that infra-red radiation-as it was called -would eventually let man see the world in an entirely new light...
...Today, infra-red detectors are providing stunning images that were once totally invisible to the naked eye (see color pages). The new medium is called color thermography-the technique of translating heat rays into color. Unlike ordinary color photographs, which depend on reflected visible light, thermograms, or heat pictures, respond only to the temperature of the subject. Thus the thermographic camera can work with equal facility in the dark or light...
...camera's extraordinary capability is built around a characteristic of all objects, living or inanimate. Because their atoms are constantly in motion, they give off some degree of heat, or infra-red radiation. If the temperature rises high enough, the radiation may become visible to the human eye, as in the red glow of a blast furnace. Ordinarily, the heat emissions remain locked in the invisible range of infra-red light...
Since World War II, there has been an intensive effort to produce better infra-red detectors for the military. In Viet Nam, for instance, such devices have often been used to detect Communist troops in even the most densely foliated jungle. Other applications include heat-seeking missiles and spy-in-the-sky satellites. One of the leaders in the field, the Barnes Engineering Co. of Stamford, Conn., has developed detectors that can "see" the dark part of a crescent moon from a quarter-million miles away...
Though their composition may vary, all these devices are based on the same technology: they are capable of transforming tiny amounts of heat into electrical currents. Once amplified, those currents are fed into a display unit that shows the rise and fall of the infra-red radiations as visible light. The display may be as uncomplicated as an ordinary light bulb whose fluctuations are recorded on photographic film. In some cases it is a more sophisticated cathode-ray tube system that produces a TV-type image...