The principles of a new method for the detection and measurement of potential difference are given, together with a description of a prototype instrument. The basis of the method consists of the use of two cyclically varying capacitors in conjunction with two resistors, or equivalent elements, to provide an ideal transducer. Devices based on this principle have input resistances which are limited only by leakage from the input conductor, and are suitable for measurements in circuits of very high resistance. Important features of the new arrangement are a completely passive input equivalent circuit, a short response time, and an improved signal‐to‐noise ratio as compared with existing electrometers.