He"li*o*stat (?), n. [Helio- + Gr. placed, standing, fr. to place, stand: cf. F. h'eliostate.]
An instrument consisting of a mirror moved by clockwork, by which a sunbeam is made apparently stationary, by being steadily directed to one spot during the whole of its diurnal period; also, a geodetic heliotrope.
© Webster 1913.