\The*od"o*lite\, 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.
Note: 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.