Goniometer

Goniometer (Gr. gonia, 'an angle;' metron, 'a measure'), an instrument used for measuring solid angles, and hence indispensable to the crystallographer. There are two kinds in use, the contact goniometer of Carangeau (which is sufficiently accurate for many purposes, but cannot be used in the case of very small crystals), and the reflecting goniometer by Dr Wollaston. In skilful hands this instrument can measure the angles of crystals only the hundredth of an inch in size. Several elaborate modifications of this goniometer are now employed by crystallographers.