Definition of "electroscope" [e•lec•tro•scope]

• An instrument used to detect the presence, sign, and in some configurations the magnitude of an electric charge by the mutual attraction or repulsion of metal foils or pith balls. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "It was found that, if the medium held her fingers at a distance of an inch or so from the knob of the electroscope, some form of energy, apparently _radio-active_ in character, issued from her fingers, and _gradually discharged the electroscope_."
• "By the side of gold leaf electroscopes we see a feather electroscope, which is fastened to its support by means of a silken thread."
• "The spectroscope will detect a quantity of matter four million times smaller even than this; and the electroscope is a million times still more sensitive than the spectroscope."