The resultant force of electrostatic attraction between two concentric hemispherical electrodes can be determined rigorously, and it is a suitable arrangement for an absolute electrostatic voltmeter.The curved electrodes have great mechanical rigidity and constancy of form.Stability of balance between the electrostatic and mechanical forces, elimination of the error introduced by the width of separation between the moving electrode and the guard electrode, and other unexpected advantages were obtained by their use.