An Attempt to Verify the Theory of the Long Spark of Loeb and Meek

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Abstract
In an attempt to verify the theory of the long spark of Loeb and Meek, d.c. sparking potentials in a plane parallel gap in air have been measured as a function of plate separation and pressure at and below atmospheric pressure. Below atmospheric pressure, the sparking-potential curve as a function of gap length at constant pressure, displays a peculiar levelling-off at large gap lengths. This has been shown to be due to field distortion of a pressure-dependent type. This field distortion is, in large measure, caused by the walls of the large chamber used in this study. This field distortion prevented the verification of the Loeb-Meek theory. However, there is considerable evidence for believing the results at atmospheric pressure to be valid. Meek's equation represents the data accurately at atmospheric pressure. Water vapor causes a small but definite scattering in sparking potentials.