An instrument consisting of a telescope so mounted as
   to have two axes of motion at right angles to each other, one of them
   parallel to the axis of the earth, and each carrying a graduated
   circle, the one for measuring declination, and the other right
   ascension, or the hour angle, so that the telescope may be directed,
   even in the daytime, to any star or other object whose right ascension
   and declination are known. The motion in right ascension is sometimes
   communicated by clockwork, so as to keep the object constantly in the
   field of the telescope. Called also an equatorial telescope.