A calculable standard of capacitance

Abstract

A calculable standard of capacitance has been constructed in the form of a variable cylindrical cross-capacitor. The value defined by the standard is the change in capacitance due to the linear displacement of one screening electrode relative to another, and this displacement is measured in wavelengths of light (Hg green, λ 5462) by means of a built-in Fabry-Perot interferometer. The capacitance interval has a nominal maximum of 0.25 pF. The estimated accuracy of a capacitance determination by means of the standard is 1 in 107 when the value is expressed in e.s.u. The present uncertainty in the value assumed for the velocity of light limits the accuracy of a result expressed in e.m.u. to 1 in 106.