ACHROMAT'IC, adjective [Gr. priv. and color.]

Destitute of color. achromatic telescopes are formed of a combination of lenses, which separate the variously color rays of light to equal angles of divergence, at different angles of refraction of the mean ray. In this case, the rays being made to refract towards contrary parts, the whole ray is caused to deviate from its course, without being separated into colors, and the optical aberration arising from the various colors of light, is prevented. This telescope is an invention of Dolland.