The usual method of making a rapid determination of the internal resistance of a voltiac cell, primary or secondary, is by means of the condenser in circuit with a ballistic galvanometer. The deflection of the galvanometer due to the discharge of the condenser is first taken on open circuit with the cell and again when the cell is on a closed circuit the known resistance. The working formula is r=d—d1 over d1xR, in which d and d1 are the different deflections of the galvanometer needle and R is the external resistance of the closed circuit. The explanation of this method can be found in Carhart and Patterson\u27s Electrical Measurements
