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Franklin's electrostatic machine


Franklin's electrostatic machine is a high-voltage static electricity generating device used by Benjamin Franklin in the mid-eighteenth century for research into electrical phenomena. Its key components are a glass globe which turned on an axis via a crank; a cloth pad in contact with the spinning globe; a set of metal needles to conduct away the charge developed on the globe by its friction with the pad; and a Leyden jar – a high-voltage capacitor – to accumulate the charge. Franklin's experiments with the machine eventually led to new theories about electricity and inventing the lightning rod.

Franklin was not the first to build an electrostatic generator. European scientists developed machines to generate static electricity decades earlier. In 1663 Otto von Guericke generated static electricity with a device that used a sphere of sulfur.Francis Hauksbee developed a more advanced electrostatic generator around 1704 using a glass bulb that had a vacuum. He later replaced the globe with a glass tube of about 2.5 feet (0.76 m) emptied of air. The glass tube was a less effective static generator than the globe, but it became more popular because it was easier to use.

Machines that generated static electricity with a glass disc were popular and widespread in Europe by 1740. In 1745, German cleric Ewald Georg von Kleist and Dutch scientist Pieter van Musschenbroek discovered independently that the electric charge from these machines could be stored in a Leyden jar, named after the city of Leiden in the Netherlands.


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