The Fall of Potential in the Initial Stages of Electrical Discharges

The fall of potential in the initial stages of condensed discharges through air, nitrogen, hydrogen and C${\mathrm{O}}_2$ has been studied as a function of the pressure. The experimental method consisted in measuring the magnitude and shape of the potential wave impressed upon two parallel, copper wires attached to the electrodes of the discharge. In every case the rate of potential fall was increased with increase of pressure. Over the pressure range studied (50 to 140 cm of mercury) the decrease of potential was slowest in C${\mathrm{O}}_2$ of the gases quantitatively studied. However, rough measurements showed the rate of fall to be very much slower in helium than in C${\mathrm{O}}_2$. In hydrogen a small overvoltage produced an increase in the rate of potential fall at all pressures. The results are shown to be in good agreement with Toepler's discharge law. A method is described by means of which it is possible to apply 5×${10}^5$ volts/cm across a spark gap in air, hydrogen or nitrogen at atmospheric pressure at least ${10}^{-6\mathrm{}}$ sec. without electrical breakdown. When such discharges once are initiated the potential falls much faster than for a static breakdown.