Theory of Current Transference at the Cathode of an Arc

Abstract

The relatively low temperaturé of the cathode in the case of such metals as copper and mercury, suggests that thermionic emission from the cathode is not essential and that some other factor may be more important in determining the current carried to the cathode in such cases. It appears that if the gas next to the cathode is sufficiently hot, thermal ionization in accordance with Saha's equation may account for much of the current to the cathode. Calculation shows that an upper limit for the required temperature is somewhat in excess of 4000°K for Ca, and 6000°K for Cu.