HIGH SPEED PHOTOGRAPHS OF VACUUM SPARKS AT VOLTAGES UP TO 250 KV

Streak and framing photographs show that light-emitting vapour first appears from the cathode at all gaps. The vapour in which the main discharge develops originates at the cathode for gaps up to about 0.5 cm, and at the anode for gaps greater than this. At these larger gaps, the anode vapour velocities are in the range 3 × 104-3 × 105 cm sec-1 which correspond to temperatures up to about 2 × 104 °K. The degree of ionization of vapour from stainless steel electrodes is less than 10-5. Simultaneous development of multiple spark channels occurs when the gap is overvolted. © 1898.