Quadrant electrometer

From Glossary of Meteorology

quadrant electrometer

A very sensitive electrostatic electrometer for measuring small potential differences.

It consists of a metal needle in the form of a lemniscate suspended horizontally inside a short metal container that has been divided into four electrically insulated quadrants. In the most frequent mode of operation, alternate quadrants are electrically connected to the terminals of a battery that has a grounded midpoint. The unknown potential is applied to the needle, causing a rotation proportional to this potential.