Author: Connolly T. F.
Publisher: Maney Publishing
ISSN: 1752-2706
Source: Survey Review, Vol.1, Iss.1, 1931-07, pp. : 21-24
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Abstract
The function of a compass is to indicate the direction of the magnetic field in its neighbourhood. Its pointing is therefore magnetic not geographical. The divergence from a true-north indication, different in different parts of the world, is the “variation” of the compass. This quantity is obviously of importance for true directional work when the magnetic compass is used. Its value is known to a high degree of accuracy and is easily available. Such accurate magnetic data are obtained from an elaborate and special form of compass known as a “Magnetometer” and are regularly published by the Astronomer Royal to an accuracy of about half a minute of arc.
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