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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Franklin's electrostatic machine | 1/3 | https://en.wikipedia.org/wiki/Franklin's_electrostatic_machine | reference | science, encyclopedia | 2026-05-05T09:37:04.008946+00:00 | kb-cron |
Franklin's electrostatic machine is a high-voltage static electricity-generating device used by Benjamin Franklin in the mid-18th 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.
== Background ==
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. In 1745, Peter Collinson, a businessman from London who corresponded with American and European scientists, donated a German "glass tube" along with instructions how to make static electricity, to Franklin's Library Company of Philadelphia. Collinson was the library's London agent and provided the latest technology news from Europe. Franklin wrote a letter to Collinson on March 28, 1747, thanking him, and saying the tube and instructions had motivated several colleagues and him to begin serious experiments with electricity.
In 1746, Franklin began working on electrical experiments with Ebenezer Kinnersley after he bought all of Archibald Spencer's electrical equipment that he used in his lectures. Later, he was also associated with Thomas Hopkinson and Philip Syng in experimentation with electricity. In the summer of 1747 they had received an electrical system from Thomas Penn. While no records exists to tell exactly what parts were included in the system, historian J. A. Leo LeMay believes it was a combination of an electricity generating machine, a Leyden jar, a glass tube, and a stool that was electrically insulated from the ground. This gave Franklin a complete system to experiment with generating and storing electricity. When amber, sulfur, or glass are rubbed with certain materials, they produce electrical effects. Franklin theorized this "electrical fire" was collected from this other material somehow, and not produced by the friction on the object. He decided to retire early from his printing business, still in his early forties, to spend more time studying electricity. In 1748, Franklin turned over his entire printing business to his partner David Hall. He moved into a new Philadelphia home with his wife, where he built a laboratory to conduct experiments and research new electrical theories. Franklin experimented not only with the electrostatic machine with the glass globe, but also with the Leyden jar. He kept a detailed journal of his research in a diary called "Electrical Minutes" that has since been lost. Franklin's machine was given to Library Company of Philadelphia by Franklin's grandson in 1792, and is currently on display at the Franklin Institute.
== Description == Franklin's machine used a belt and pulley system that could be operated by one person turning a crank. A large pulley was attached to the crank handle, and a much smaller pulley was attached to a large glass globe. An iron axle passed through the globe. This allowed the globe to be rotated at high speed. When the crank was turned, the glass globe rubbed against a leather pad, which generated a large static charge, similar to the electrical charge that could be created by rubbing a glass tube with wool cloth by hand. The machine was unique improvement over others made in Europe at the time, as the glass globe could be spun faster with much less labor. A few revolutions of the handle were all that were needed to charge a Leyden jar. The electricity produced by the machine, in the form of sparks, passed through a set of metal needles positioned close to the spinning globe. The electric charge continued passing through a beaded iron chain, which acted as a conductor, to a Leyden jar that received the electricity. Franklin called the sparks produced by the machine "electrical fire". The glass globes, known as "electerizing globes", were made of glass that was scientifically designed to produce static electricity effectively. Franklin specified the materials to be used in the glass formula, and the globes were manufactured by Caspar Wistar, a close associate of Franklin. Wistarburgh Glass Works also made scientific glass for the Leyden jars Franklin used in the 1750s.