Spĕc'trum, n.

n.; pl. SPĒ'CTRĪ. [Lat. See SPEC-TER.] 1. A visible form; something seen. Darwin. 2. (Opt.) The several colored and other rays of which light is composed, separated by the refraction of a prism or other means, and exhibited either as spread out on a screen or by direct vision.

Chemical spectrum, the rays of the solar spectrum which produce chemical effects, as in photography, having their maximum influence at and beyond the violet rays. — Chromatic spectrum, the visible, colored rays of the solar spectrum, exhibiting the seven principal colors in their order, and covering the central and larger portion of the space of the whole spectrum. — Ocular spectrum, an image which the eye, after viewing an object attentively, and then turning from it, sees of the object in its complementary colors, as a green image seen after viewing a red wafer lying on white paper. — Solar spectrum, a spectrum formed by solar light, especially as thrown by a prism on a screen in a darkened room. — Spectrum analysis, chemical analysis effected by comparison of the different relative positions and qualities of the fixed lines of spectra produced by flames, in which different substances are burned or evaporated, each substance having its own characteristic system of lines. — Thermal spectrum, the heating rays of the solar spectrum, which have their maximum effect at and beyond the red rays.