Sparks “Standard for Low Values of Direct Capacitance

In the measurement of small capacitances, such as the interelectrode capacitance of vacuum tubes, standards are needed for checking the calibration of the measuring equipment. The design, construction, and measurement of a group of small primary and secondary stand-ards of capacitance for this purpose are described, the values of which range from 0.001 to 5.0 micromicrofarads. Capacitators of 0.1 fi/xf and above are of the Kelvin guard-ring type; those of 0.1 fifif and smaller are of a new "guard-well " type, which permits the construction of primary standards for values as low as desired. I