The measurement of electrostatic potential attributable to net ion space charge in air

The electrostatic potential in air resulting from an ion space charge of one predominant sign is difficult to measure with existing potential-measuring instruments. An ideal instrument should not deplete the ion space charge and should be capable of measuring relatively low potentials. An instrument using the null-and-substitution method, and combining an electronic pulse widener and a vacuum-tube voltmeter, is described. This instrument has an application in measuring ion density in air by measuring the electrostatic potential attributable to ion space charge; Poisson's equation can then be solved for ion density.