[AS.] A bow or arch in the sky opposite to the sun in time of rain, caused by the rays of light breaking up into their seven separate colors as they fall on the' rain-drops. (See Prism, Spectrum, Light.) Rainbows sometimes occur on the spray rising from waterfalls. Most rainbows are seen in the afternoon, when the sun is in the west, and sometimes in the morning, but never at noon, because then the sun is above us, and we cannot stand between it and the rain. When there is a double rainbow the inner is the primary, and the outer the faint or secondary one.