Electrical Conduction Across Minute Air-Gaps

Abstract

Electrical Conduction across Minute Air-gaps.—As some results obtained by R. W. Wood are at variance with those of other observers, further experiments seemed desirable in which the separation of the metallic electrodes was determined optically. Therefore, two optical surfaces of nearly the same curvature were made conducting by depositing gold upon them by cathode discharge and were supported so as to be nearly in contact. Then, as the upper one was semi-transparent, the distance apart was determined by the interference rings produced by light of wave-length 0.546 μ. Using voltages of from 1.5 to 60, the minimum distance at which no conduction took place and the maximum distance at which conduction occurred were observed. Both these distances varied from less than a wave-length to several wave-lengths. In some cases the resistance of the gap during conduction was measured; it was found to obey Ohm's law and to be unaffected by radiation from 3 mg. of radium. The results suggest that the conduction was due to small projections from the electrodes or to dust particles. No disruptive discharge took place even when the potential gradient rose to 640,000 volts/cm., probably becuase the potential was less than the minimum which previous researches had indicated is necessary.