The paper describes a method of determining the polarization capacity of an electrolytic cell consisting of platinum electrodes in sulphuric acid. Across the cell is placed a condenser of known capacity, and the system is short-circuited. The short circuit is broken and a second condenser of known capacity is charged to a known potential and then discharged into the system. The first condenser is disconnected from the electrolytic cell and from the second condenser and then discharged through a ballistic galvanometer. Hence the potential difference attained by the electrolytic cell, which is the same as that of the first condenser, is calculated. It is impracticable to determine the potential difference from a discharge of the second condenser, because of the residual effects.The depolarization of the cell is rapid and the potential difference immediately after discharge of the second condenser into the system is deduced by varying discontinuously the time of contact of the cell with the first condenser. The various connexions and disconnexions are made by means of a falling vulcanite plate on which are specially shaped brass plates,which, during the fall of the plate, pass over suitably placed connecting brushes.That the results obtained mean something definite and are substantially accurate is proved by the determination of certain polarization capacities by (I) a bridge method, using alternating currents provided by triode-valves, and (2) the falling plate method. The values obtained by the two methods are in substantial agreement.