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Show "Invisible Light" to Aid Man's Sight BALTIMORE,, MD. Invisible light Is opening up a new field for transmission of secret signals In warfare and for detection of chemical frauds and forgeries, Dr. Robert W. Wood, professor of experimental experi-mental physics at Johns Hopkins university, uni-versity, asserted at a public session of the sixty-ninth meeting of the American Chemical society. Infra-red rays, the long light waves which ordinarily produce no color sensation sen-sation to the eye, can be employed, lie explained, in military signal lamps for flashing signals which can be seen only by observers using field glasses equipped with a special screen similar to that in the lamp. "Signals can be transmitted in this manner in full sunlight for a distance of from five to eight miles, depending on atmospheric conditions," he said. "It has been found that these rays " cause a marked change in the appearance ap-pearance of objects. An airplane, for instance, could be painted with an enemy en-emy Insignia which, however, would not mislead friendly troops equipped with special binoculars by which the true Insignia would be visible. ' "This property of certain pigments and dyes to alter their relative lmni-! lmni-! nosity when illuminated by near in fra-red rays is now being used to produce pro-duce stage effects. A drop can ba painted so as to represent a summer scene under ordinary light and a winter win-ter scene under near infra-red rays." He then demonstrated how ultraviolet ultra-violet light, the shorter rays at the other end of the spectrum, Illuminated Illumin-ated a phosphorescent scene at the other end of the room, although the rays themselves were invisible. He told how he had utilized this principle prin-ciple to devise an invisible light for nigiit use on warships and convoys so that thev would not be seen by an enemy's submarines, although observers observ-ers on other vessels of the friendly fleets could observe the lights by use of phosphorescent telescopes. "The same principles are now used he said, in detecting forgeries and clever alterations of documents. The chemicals used In such frauds can be detected when they are .llumlnated by ultra-violet or infra-red rays, "professor Wood declared that use of invisible light opened up field for medical research and that it might prove of value in detecting the presence of cancerous and other ab- o,". tissues in eases conditions were not evident under or dinary light. |
