A technique used in electrical prospecting requiring artificial currents. It is based on the principle that if two electrodes are inserted in the ground and an external voltage is applied across them, there will be a flow of current through the earth from one electrode to the other. If the medium through which the current flows is homogeneous in its electrical properties, the flow lines will be regular and in a horizontal plane, symmetrical about the line joining the electrodes. Any inhomogeneities in these properties will cause distortions in the lines of current flow. Such distortions indicate the existence of buried material with either higher conductivity than its surroundings, so that it attracts the flow lines toward itself, or with lower conductivity, so that it tends to force the lines into the surrounding medium.