An electrostatic instrument that detects small potential differences and electric charges. The gold-leaf electroscope consists of a pair of gold leaves hanging side by side from an insulated metal support enclosed in a draught-proof case. If a charge is supplied to the support the leaves separate due to their mutual repulsion. A more precise form replaces one of the gold leaves by a rigid metal plate (see diagram). Lauritzen’s electroscope utilizes metallized quartz fibre as the sensitive element.
An instrument that is capable of accurate quantitative measurement of potential difference is called an electrometer.