HELIOSTAT

He″li‐o‐stat (?), n. [[Helio- + Gr. � placed, standing, fr. � to place, stand: cf. F. héliostate.]] 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.