XIII. The electrical conductivity imparted to a vacuum by hot conductors

Abstract

The experimental part of the present paper is an investigation of the electrical conductivity of the space surrounding hot surfaces of platinum, carbon, and sodium at low pressures. A preliminary account of some of the experiments on platinum was read before the Cambridge Philosophical Society on November 25th, 1901. The conductivity produced by hot metals has been the subject of a great number of researches by different authors. The phenomena are, however, very complicated; for the quantity and sign of the ionisation is found to vary in the most remarkable manner with the nature, temperature, and previous history of the metal, with the nature and pressure of the surrounding gas, and with small changes in the state of the metal surface. The present investigation was undertaken with the idea that in the negative ionisation at high temperatures the conductivity produced by metals took its simplest form. This idea is supported by the observation of Professor McClelland, that the negative current is to a great extent independent of the nature of the gas, and is independent of its pressure over a range from ∙04 to ∙004 millim.