Goniometer

[Sarah]

An instrument for measuring angles, especially the angles ofcrystals, 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 fixedpoint, which is the center of the graduated circle or semicircle uponwhich the angle is read off.-- Reflecting goniometer, an instrument for measuring the angles ofcrystals by determining through what angular space the crystal mustbe turned so that two rays reflected from two surfaces successivelyshall have the same direction; -- called also Wollaston's goniometer,from the inventor.