Theodolite

theodolite

An instrument used, especially in trigonometrical surveying, for the accurate measurement of horizontal angles, and also usually of vertical angles. It is variously constructed.

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.

Origin: Probably a corruption of the alidade. See Alidade.

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