The direct-voltage calibration of air-gaps in a uniform field and between spheres up to 25 cm in diameter

Direct breakdown voltages of gaps between spherical and plane electrodes in air have been measured under controlled test conditions using 2.0, 6.25, 12.5 and 25cm-diameter spheres. The factors which influence the breakdown voltages have been studied systematically and their effect on the calibration data is discussed. Calibration Tables for sphere-gaps and uniform-field gaps are given, and the results are compared with the new values recently issued by the I.E.C.