Electroscope
Nollet's device detects and measures electric charge. Jean-Antoine Nollet (1700-1770) was the first professor of experimental physics at the university of Paris. At that time electrostatics was a topic of great interest. Nollet's electroscope was designed to detect and crudely measure electric charge. An insulated charge sensor protruded into a cylindrical container, the ends of which were closed by two flat glass windows. The bottom of the sensor (the part in the cylinder) was fitted with two leaves of metal foil ( usually gold). If the sensor's opposite, extruding end was brought into contact with a negatively charged body, electrons were repelled into the two leaves and they separated. The degree of separation was function of the size of he charge. A second negatively charged body contacting the extruding end would cause the leaves to separate more, whereas a positively charged body subsequently applied to the same end would cause the separation to decrease.