Contemporary Advances in Physics, XXIV - High-Frequency Phenomena in Gases, First Part

N this article I will describe some of the phenomena which are observed when the voltage across a region filled with gas is varying quite rapidly. Considered as a function of time, the voltage may be periodic, a sine-wave with uniform amplitude and of a frequency somewhere between a few thousands and a few hundreds of millions of cycles per second. It may be a succession of highly-damped wavetrains, each commencing with a rapid rise of voltage and continuing in oscillations of high frequency but swiftly declining amplitude, which die away into nothing and after an interval (it may be of a few hundredths or a few thousandths of a second) are followed by another train. It may be a brief irregular spasm of electromotive force, of which the highest value of the voltage is measured or merely guessed. In the gas itself there may be the phenomenon of sudden and violent breakdown; or the establishment of a self-sustaining luminous discharge, like in aspect to a glow or an arc; or merely a vibratory motion of electrons, freed by other agencies and set in motion by the oscillating field. One might regard this as a subject which physicists had better leave alone, until they have full understanding of the seemingly much easier problems of discharges across a gas exposed to a constant voltage. So great are the apparent advantages of steady or "directcurrent" discharges for the student, so great the apparent inconveniencies of high frequencies, that one might reasonably think it futile to assail the latter with weapons which have not yet overcome the former.