An Explanation of the Tanberg Effect

• DOI: 10.1038/179625a0
• Publication Date: 2006-05-30T22:27:59Z
• Authors: A. E. ROBSON; A. VON ENGEL

WHEN an arc discharge at very low pressure passes between metal electrodes the cathode experiences a force directed away from the anode. By suspending a copper cathode on a pendulum and observing the deflexion Tanberg1 measured this force. At the same time he measured the rate of evaporation of cathode material. With these data he obtained the velocity of the evaporating atoms from Newton's laws of motion. From a force of 20 dynes/amp. and a rate of evaporation of 10−5 gm./coulomb, he estimated that the copper atoms left the cathode with a velocity of about 106 cm./sec. He suggested from this that the cathode was at a temperature of about 5 × 105 deg. C. Up to the present his claim has caused some concern. Opinions are divided into two groups: those who question the accuracy of the experiments and those who disbelieve in Newton's laws. However, other evidence2–4 tends to support Tanberg's measurements.