# goniometer

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## goniometer

[‚gō·nē′äm·əd·ər]
(electromagnetism)
An instrument for determining the direction of maximum response to a received radio signal, or selecting the direction of maximum radiation of a transmitted radio signal; consists of two fixed perpendicular coils, each attached to one of a pair of loop antennas which are also perpendicular, and a rotatable coil which bears the same space relationship to the coils as the direction of the signal to the antennas.
(engineering)
An instrument used to measure the angles between crystal faces.
An instrument which uses x-ray diffraction to measure the angular positions of the axes of a crystal.
Any instrument for measuring angles.

## Goniometer

(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 It was later superseded to a considerable degree by X-ray structural analysis.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

Figure 1. Single-disk reflecting goniometer: (a) overall view; (b) diagram. C is the collimator, T is the viewing tube, L is the limb, ν is the vernier, and N1 and N2 are normals corresponding to facets a and b. to a ruler; it permits measurement of angles with an accuracy of 0.25°-0.5°. A more precise reflecting goniometer is shown in Figure I.

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’.

### REFERENCES

Flint, E. E. Prakticheskoe rukovodstvo po geometricheskoi kristallografii, 3rd ed. Moscow, 1956.
Flint. E. E. Nachala kristallografii, 2nd ed. Moscow, 1961.

(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.

## goniometer

i. A direction-finding device commonly used in radio location and radio navigation. It has a fixed antenna, and the direction response is varied electrically. Using a method called phase comparison, it senses the angle between a fixed reference point and the direction from which a radio signal is being received. See automatic direction finder.
ii. A motor-driven instrument used with four stationary aerials to a deliver rotating signal field for VOR (very high frequency omnidirectional radio-range).
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