1. Observation of electric fields caused by current introduced into the ground as a means for studying earth resistivity. The term normally includes only those methods in which a very low frequency or direct current is used to measure the apparent resistivity. Includes electric profiling and electric sounding (q.v.). Various arrays (q.v.) are used. See also Gish-Rooney method and Lee partitioning method. 2. Sometimes also includes polarization and electromagnetic methods (q.v.).