Goniometer

Part of speech: noun (n.)

An instrument for measuring angles, especially the angles of crystals, or the inclination of planes. Contact, or Hand, goniometer, a goniometer having two movable arms (ab, cd), between which (at ab) the faces of the crystals are placed. These arms turn about a fixed point, which is the center of the graduated circle or semicircle upon which the angle is read off. -- Reflecting goniometer, an instrument for measuring the angles of crystals by determining through what angular space the crystal must be turned so that two rays reflected from two surfaces successively shall have the same direction; -- called also Wollaston's goniometer, from the inventor.