Improved equipment for measuring Earth‐current potentials and earth‐resistivity

Abstract

Although other methods have been proposed for determining the density and direction of the natural electric currents which flow in the Earth's crust, those which have thus far been put into use require two classes of measurements, namely, measurements of the differences of potential between points in the Earth taken in such a way as to yield the potential gradient, and measurements constituting a survey of earth‐resistivity in the region where the potential measurements are made.Earth‐current observations heretofore have been incomplete, in that the resistivity measurements have not been undertaken. A method has been developed and is now in use at the Watheroo Magnetic Observatory of the Carnegie Institution of Washington by which it is possible to obtain a fair knowledge of the distribution of earth‐resistivity, both laterally and with depth. From these two types of measurements, the density and direction of the earth‐currents can be determined. The method of measuring potentials which has been in operation at the Watheroo Observatory for over two years, although modeled upon schemes previously used elsewhere, contains some novel features which seem to be genuine improvements.