The results of the measurement at a frequency of 1 million cycles per sec. of the effective inter-electrode capacitances under working conditions of a variety of valves are tabulated, together with an estimate of the net capacitance residing between the active elements themselves.The grid-filament capacitance shows an increment which increases with anode current up to the point at which grid current flows. The increment diminishes at a given value of anode current as the anode voltage is increased. Experiment shows that. this increment in; capacitance is not a simple function of anode current, neither .of anode-filament nor of mutual conductance. It is augmented the higher the filament temperature and is probably fc. function of the initial velocity of the electrons.The effective grid-anode capacitance suffers a reduction as the anode current increases, but the reduction is much smaller, proportionately than the increase in grid-filament capacitance.Every type of valve examined displays the effect—even the small acorn trdodes and. pentodes, in which the increment represents a 50% augmentation of the “cold” value ofCfg.