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The electroscope is an early scientific instrument used to detect the presence of electric charge on a body. It detects this by the movement of a test charge due to the Coulomb electrostatic force on it. The amount of charge on an object is proportional to its voltage. The accumulation of enough charge to detect with an electroscope requires hundreds or thousands of volts, so electroscopes are used with high voltage sources such as static electricity and electrostatic machines. An electroscope can only give a rough indication of the quantity of charge; an instrument that measures electric charge quantitatively is called an electrometer.

Pith-ball electroscope
In 1731, Stephen Gray used a simple hanging thread, which would be attracted to any nearby charged object. This was the first improvement on Gilbert's versorium from 1600. The pith-ball electroscope, invented by British schoolmaster and physicist John Canton in 1754, consists of one or two small balls of a lightweight nonconductive substance, originally a spongy plant material called pith, suspended by silk or linen thread from the hook of an insulated stand. Tiberius Cavallo made an electroscope in 1770 with pith balls at the end of silver wires. of the atoms inside the pith ball. All matter consists of electrically charged particles located close together; each atom consists of a positively charged nucleus with a cloud of negatively charged electrons surrounding it. The pith is an insulator, so the electrons in the ball are bound to atoms of the pith and are not free to leave the atoms and move about in the ball, but they can move a little within the atoms. See diagram. If, for example, a positively charged object (B) is brought near the pith ball (A), the negative electrons (blue minus signs) in each atom '' will be attracted and move slightly toward the side of the atom nearer the object. The positively charged nuclei (red plus signs) will be repelled and will move slightly away. Since the negative charges in the pith ball are now nearer to the object than the positive charges (C)'', their attraction is greater than the repulsion of the positive charges, resulting in a net attractive force. This separation of charge is microscopic, but since there are so many atoms, the tiny forces add up to a large enough force to move a light pith ball. If the external object (B) instead has a negative charge, the positive nuclei of each atom will be attracted toward it while the electrons will be repelled away from it. Again, this causes opposite charges to be closer to the external object than charges of the same polarity, resulting in a net attractive force. The pith ball can be charged by touching it to a charged object, so some of the charges on the surface of the charged object move to the surface of the ball. Then the ball can be used to distinguish the polarity of charge on other objects because it will be repelled by objects charged with the same polarity or sign it has, but attracted to charges of the opposite polarity. Often the electroscope will have a pair of suspended pith balls. This allows one to tell at a glance whether the pith balls are charged. If one of the pith balls is touched to a charged object, charging it, the second one will be attracted and touch it, communicating some of the charge to the surface of the second ball. Now both balls have the same polarity charge, so they repel each other. They hang in an inverted 'V' shape with the balls spread apart. The distance between the balls will give a rough idea of the magnitude of the charge. == Gold-leaf electroscope ==
Gold-leaf electroscope
The gold-leaf electroscope was developed in 1787 by British clergyman and physicist Abraham Bennet, It consists of a vertical metal rod, usually brass, from the end of which hang two parallel strips of thin flexible gold leaf. A disk or ball terminal is attached to the top of the rod, where the charge to be tested is applied.The Bohnenberger electroscope was developed in the early 19th century by the German physicist Johann Gottlieb Friedrich von Bohnenberger as an improvement on earlier gold-leaf electroscopes. The instrument employed a single gold leaf suspended between two oppositely charge plates, increasing sensitivity and allowing clearer detection of both the presence and sign of an electric charge. Bohnenberger electroscopes were widely used in 19th-century experimental physics and appear in university laboratories, teaching collections, and scientific manuals throughout Europe. The design influenced later high-sensitivity electroscopic instruments. Eberbach & Son electroscope instruments were designed primarily for educational and laboratory use, following classical electroscope principles while emphasizing robustness and standardized construction for teaching environments. While they did not introduce new electroscopic principles, they played a role in the standardization of electrostatics instruction in North America. File:Gold-leaf electroscope-2.jpg|Condensing electroscope, Rome University physics dept. File:Gold leaf electroscope with ground strips.png|Electroscope from about 1910 with grounding electrodes inside jar, as described above File:Gold leaf electroscope homemade.jpg|Homemade electroscope, 1900 == See also ==
Source: Wikipedia ↗
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