This paper gives the results of an investigation of the voltage characteristic of the copper arc in air during the process of arc formation. A pair of copper electrodes, initially in contact and carrying current, were separated and the voltage arising across the arc gap was studied. Cathode‐ray oscillograms indicate that at the instant of contact separation there develops across the gap a voltage of about 12.2 volts. This voltage was attained in less than 10−5 seconds. This rapidly developed voltage was found to be independent of arc current for current values up to 100 amperes, which suggests that the rapidly developed initial voltage corresponds to the cathode fall of the arc.