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Grating, Diffraction.—A series of fine parallel lines on a surface of glass, or polished metal, ruled very close together, at the rate of 10,000 to 20,000 or even 40,000 to the inch; distinctively called a diffraction or a diffraction grating, much used in spectroscopic work.
Gray.—A color having little or no distinctive hue (chroma) and only moderate luminosity.
Green.—The color of ordinary foliage; the color seen in the solar spectrum between wave lengths 0.511 and 0.543 micron.
Emerald Green.—A highly chromatic and extraordinarily luminous green of the color of the spectrum at wave length 0.524 micron. It recalls the emerald by its brilliancy, but not by its tint; applied generally to the aceto-arsenate of copper. Usually known as Paris green.
High Color.—A hue which excites intensely chromatic color sensations.
HUE.— Specifically and technically, distinctive quality of coloring in an object or on a surface; the respect in which red, yellow, green, blue, etc., differ one from another; that in which colors of equal luminosity and CHROMA may differ.
Indigo.—The violet-blue color of the spectrum, extending, according to Helmholtz, from G two-thirds of the way to F in the prismatic spectrum. ‘The name was introduced by Newton, but has lately been discarded by the best writers.
Light.—Adjective applied to colors highly luminous and more or less deficient in chroma.
Luminosity.—Specifically, the intensity of light in a color, measured photometrically; that is to say, a standard light has its intensity, or vis viva, altered, until it produces the impression of being equally bright with the color whose light is to be
