A Comparison of Alternating and Direct Spark Potentials

TPHE potential required to produce a disruptive discharge across a -*• spark gap has received the attention of many investigators.Until comparatively recent years these measurements have been chiefly concerned with direct current, the source of potential usually being a Holz or a Wimshurst machine.A fairly complete list of these contributions beginning with the work of Lord Kelvin in i860 may be found in J. J. Thompson's " Conduction of Electricity through Gases/' 1 With the development of high-frequency oscillatory discharges such as are used in wireless telegraphy, and high tension alternating current for the transmission of power, the question of alternating spark potentials has received the attention of engineers and physicists because of the practical value attached to such information.Steinmetz 2 has measured the A.C. potential required to produce a spark in air at ordinary pressures and found a practically linear relation between potential and spark distance up to no-KV.efl with a commercial current of 125 cycles.Muller, 3 who used a different method, obtained similar results.Toepler 4 has collected tables from Freiberg, Jona, Steinmetz and others and attempted to reduce all to standard conditions for purposes of comparison, but with unsatisfactory results.Kowalski and Rappel 5 have made one of the most careful series of measurements and found their mean effective values for alternating potentials from 4 to 6 per cent.lower than those given by Toepler.Among others who have worked 1