A simple feedback system has been developed for application to either a field‐interrupting electrostatic modulator or to a vibrating electrode modulator; this system substantially increases the stability, sensitivity, and accuracy of the electrostatic voltmeter in which it is employed. An accuracy of 0.2% and a response rate of 2000 V/sec have been achieved in this instrument, which incorporates a transparent, vibrating NESA glass electrode to facilitate sample illumination.