Dependence of the Dielectric Coefficient of Air Upon Pressure and Frequency

Abstract
A capacity-resistance bridge has been designed to incorporate into an a.c. method of measurement the most desirable features of a previously described electrometer method of determination of the dielectric coefficients of gases. The bridge, which provides for adequate shielding from the effects of solid insulators, has been employed for the measurement of the dielectric coefficient of air at pressures up to 170 atmospheres (18°C) and frequencies up to 70,000 cycles per second. As in the electrometer measurements, the dielectric coefficient at each frequency employed appeared to increase approximately linearly with pressure. The extreme variation among the measured values of the dielectric coefficient, 1.000589 to 1.000593 at N.T.P., was less than one percent, and is considered to lie within the experimental error.

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