A method of measuring the effective electromotive force and internal resistance of a galvanic cell during current flow is described. A dry cell was used for demonstration of the method. By introducing a reference electrode into a cell consisting of an iron electrode and a magnetite electrode in wet clay, it was possible to measure the potential and, resistance between the reference electrode and either the iron or magnetite during current flow. When the iron and magnetite were short‐circuited, the potential and resistance between the reference electrode and the iron‐magnetite couple were measured. By impressing current upon the galvanic couple from an auxiliary electrode, the potential‐current characteristic of the couple was determined. It was shown that an iron plate in wet clay exhibits such a characteristic similar to that of the galvanic couple.