THEORY AND PRACTICE OF LOW‐FREQUENCY ELECTROMAGNETIC EXPLORATION

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Abstract
Based directly on Maxwell’s Field Equations, the extremely low end of the frequency spectrum may be reduced in first approximation to simple potential theory. The approximation theory is borne out by some field experiments, the results of which are presented. Agreement with the theory, however, requires that the ground have a very large effective dielectric constant. This conclusion is supported by previous observations by a number of independent observers. Thus, the relaxation time has been found to be extremely great, not only in observations directly on the ground, but also in small samples of mud, and the sign of an electric anomaly over a relative insulator, such as crystalline salt or gas and oil, invariably has been found to be negative. Both of these observations can be explained in terms of a very great dielectric constant. The value yielded by the present experimental work is of the order of [Formula: see text].

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