electroscope, n. [Electro- + -scope: cf. F. électroscope.].
An instrument for detecting the presence of electricity, or changes in the electric state of bodies, or the species of electricity present, as by means of pith balls, and the like. [1913 Webster]
Condensing electroscope (Physics), a form of electroscope in which an increase of sensibility is obtained by the use of a condenser.