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More than three and a half centuries ago, Newton discovered the spectrum; but he saw only the visible radiations: he had no means of learning that, beyond the violet edge, ultraviolet radiation was impinging, and that, beyond the red edge, infra-red radiation was present. Yet these and other radiations differ physically only in wave-lengths and frequency of vibration from the relatively small radiations visible to the naked eye. And this science of the invisible rays is relatively recent, but so important that it is becoming commonplace in medicine. In view of this, the book by Luckiesh is a valuable source for those who desire to have explained in clear, understandable terms the physics of light. Particularly well written is the introduction, which takes up the spectrum, the units (Angström, millimicron, micron) of measurement, the table of wave length of various spectral regions, and the discussion of the chronological research leading
Ultraviolet Radiation: Its Properties, Production, Measurement and Applications.. JAMA. 1923;81(1):63. doi:10.1001/jama.1923.02650010067030