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Reflecting power of K and Na, for wavelengths from 0.25 to 0.55 ju. (1) Normal incidence (io°). Opaque mirrors in contact with fused quartz were tested with monochromatic light from a mercury arc. A sodium photoelectric cell was used to compare the intensities of incident and reflected beams. It was found that sodium maintains a remarkably high reflecting power throughout the ultra-violet, increasing slightly from a flat minimum near 3600A to 80 per cent, at 2536A. The reflecting power ofdoi:10.1103/physrev.15.110 fatcat:zzvbqedftberfgtbs7yykj5icu