Sixty-Cycle Calibration of the 50-Centimeter Sphere Gap

1. Ultraviolet radiation of the spheres materially improved the consistency of the sphere gap. 2. As compared with the nonirradiated gap the spark-over spacing of the irradiated gap was slightly but definitely increased over the whole range. 3. The curve of the nonirradiated gap checks the calibration as given in AIEE Standards No. 4 up to approximately 300 kv but falls below standard curve above this point. 4. The vacuum-tube type crest voltmeter used in conjunction with a capacitance potential divider was found to be very satisfactory and convenient both for calibrating the sphere gap and for everyday measurements of 60-cycle crest voltages.