Infra-red rays are hard to observe; their waves are too long to be seen as light and too short to be heard in radio receivers. But they can be measured as heat on a bolometera machine with metal strips whose electrical conductivity is altered by heat rays falling on them.
Last fortnight Dr. Donald H. Andrews of Johns Hopkins University described a bolometer to top them all. Its sensitive surface is columbium nitride cooled by liquid hydrogen to minus 432° F. At this temperatureclose to absolute zerocolumbium nitride becomes "superconductive"; its electrical resistance almost vanishes. When a heat ray hits it...
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