A frequency-bridge: An apparatus for accurate determination of frequency, by means of a null method

AS long as there was not available in the labaratory any convenient source of alternating current of a satisfactory steadiness and purity, the technique of measurements had to confine itself to such alternating-current bridge-methods where the balance is independent of frequency, so that accidental changes in frequency do not seriously affect the setting, and a reasonable amount of harmonics does not prevent an accurate adjustment. The steadiness and purity of the output from a properly adjusted triode oscillator, however, makes it possible, in a modern laboratory, to take up and successfully apply many convenient methods of measurement, which although known since many years, have been discarded and forgotten for reasons suggested above. On the other hand it enables us to utilize new methods, where the frequency enters explicitly into the result.