goniometer(redirected from arthrometer)
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(1) In physics, an instrument for measuring the angles between the planes of crystals, and also for measuring the angles of various prisms. Crystals can be distinctively characterized by the angles between their facets. Before the discovery of X-ray structural analysis, the method of measuring crystals with a goniometer was the main means of diagnosing crystalline substances. It was later superseded to a considerable degree by X-ray structural analysis.
Goniometers may be of the contact or reflecting types. The simplest contact goniometer consists of a protractor attached
A crystal attached to a rotating axis is illuminated by a collimated beam of light, and the rays reflected from its facets are observed in sequence by looking into a viewing tube T (a single-circle goniometer). The angles of rotation of the crystal are read from a scale. In more advanced two-circle goniometers (developed by Fedorov, Gol’dshmidt, and Chapskii), the crystal or the viewing tube can be rotated about two axes. The precision of measurement is to within l’ to 10’-20’.
REFERENCESFlint, E. E. Prakticheskoe rukovodstvo po geometricheskoi kristallografii, 3rd ed. Moscow, 1956.
Flint. E. E. Nachala kristallografii, 2nd ed. Moscow, 1961.
M. P. SHASKOL’SKAIA
(2) In anthropology, a goniometer is an instrument for measuring angles of curvature of the spine, the facial angle, the angle of the nose, and so on. A contact goniometer consists of a graduated metal plate in the form of an arc; its ends are joined by a transverse plate with a rotating pointer with a plumb bob attached to its center. The goniometer is attached to dividers (for example, of the sliding type), and the size of the angle being measured is determined by the distance of deflection of the pointer from the vertical.
ii. A motor-driven instrument used with four stationary aerials to a deliver rotating signal field for VOR (very high frequency omnidirectional radio-range).