The effect of an anode hole on measurements of Townsend's $\alpha$

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Abstract
The electric field between uniform field electrodes is distorted by the presence of holes in the anode, drilled to admit ultra-violet light. The distortion has been determined using a high speed digital computer, and the results have been used to calculate the errors to be expected when measurements of Townsend's first ionization coefficient α are made using such a system. In some circumstances there is an error of about 2% in α, even when the electrode spacing is 20 times the hole radius.