-s form of heliostat
n. 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.
(heliostat 的第三人称 -s形式) n. 日光反射装置
[医] 定日镜