Electrometer, after Horace-Benedict de Saussure (1786)

In this small bell-jar, two pith-balls are on fine threads on a conductor, that passes through the top of the bell-jar and terminates in a hook. When the hook makes contact with an electric charge, the pith-balls will move apart because they have an equal charge. The more the balls move apart, the larger the electric charge. The idea to use pith-balls for the measurement of electric charge comes from the British John Canton. His idea was elaborated by Horace-Bénédict de Saussure. For his research into electricity in the atmosphere (atmospheric electricity), he put a bell-jar over the pith-balls. He did this to prevent any influence of air currents. The electrometer was made by the Swiss instrument makers Paul - father and son. Around 1800 they made various meteorological instruments.