<P> An electroscope is an early scientific instrument that is used to detect the presence and magnitude of electric charge on a body . It was the first electrical measuring instrument . The first electroscope, a pivoted needle called the versorium, was invented by British physician William Gilbert around 1600 . The pith - ball electroscope and the gold - leaf electroscope are two classical types of electroscope that are still used in physics education to demonstrate the principles of electrostatics . A type of electroscope is also used in the quartz fiber radiation dosimeter . Electroscopes were used by the Austrian scientist Victor Hess in the discovery of cosmic rays . </P> <P> Electroscopes detect electric charge by the motion of a test object due to the Coulomb electrostatic force . Since the electric potential or voltage of an object with respect to ground equals its charge divided by its capacitance to ground, an electroscope can be regarded as a crude voltmeter . However, the accumulation of enough charge to detect with an electroscope requires hundreds or thousands of volts, so electroscopes are only used with high - voltage sources such as static electricity and electrostatic machines . Electroscopes generally give only a rough, qualitative indication of the magnitude of the charge . An instrument that measures charge quantitatively is called an electrometer . </P> <P> The pith - ball electroscope, invented by British schoolmaster and physicist John Canton in 1754, consists of a small ball of lightweight nonconductive substance, originally a spongy plant material called pith, although modern electroscopes frequently use plastic balls . The ball is suspended by a silk thread from the hook of an insulated stand . In order to test the presence of a charge on an object, the object is brought near to the uncharged pith ball . If the object is charged, the ball will be attracted to it and move toward it . </P>

Which property is used ti identify the electric charge on the object