Effect of a magnetic force on the motion of negative ions in a gas

Abstract

1. When the velocity of a charged particle in a gas is proportional to the electric force and inversely proportional to the pressure, the size of the particle is unaltered either by changes in the pressure or in the force. For a large range of pressures and forces the mass of an ion is thus shown to be constant, since the velocity is proportional to the ratio X / P. At low pressures when the ratio X / P exceeds a certain value the velocity of the negative ions undergoes large changes when small variations are made in the force or in the pressure. The increase in the mobility may be explained on the hypothesis that the mass associated with the negative ion diminishes. Thus in dry air at a pressure of 29 mm. the velocity of the negative ions is 926 cm. per second, under a force of 2·3 volts per centimetre, whereas if the ion travelled with the same mass that it has at atmospheric pressure the velocity would be about 114 cm. per second.