n. An arrangement of two photographic cameras, the plates of which may be brought into exactly the same plane, used in surveying and map making. From the differences between two pictures taken at the same moment, measurements in all dimensions of the region may be obtained. [ Webster 1913 Suppl. ]

n. [ Probably a corruption of the alidade. See Alidade. ] An instrument used, especially in trigonometrical surveying, for the accurate measurement of horizontal angles, and also usually of vertical angles. It is variously constructed. [ 1913 Webster ]

☞ The theodolite consists principally of a telescope, with cross wires in the focus of its object glass, clamped in Y's attached to a frame that is mounted so as to turn both on vertical and horizontal axes, the former carrying a vernier plate on a horizontal graduated plate or circle for azimuthal angles, and the latter a vertical graduated arc or semicircle for altitudes. The whole is furnished with levels and adjusting screws and mounted on a tripod. [ 1913 Webster ]