Measurements of the variation with depth of the main geomagnetic field

Abstract

The main geomagnetic field is attributable either to some deep-seated phenomena within the earth or to a fundamental property of rotating matter in which the source of the field would be distributed throughout the whole earth. The two types of explanation predict a different variation of the components of the main field with depth within the crust and can be tested by direct measurement in suitable localities. Measurements in five mines in northern England are presented and discussed, and they provide evidence in favour of the core theory.