The Leyden jar is the ancestor of our modern capacitor. As experimentation with electricity progressed through the 18th century, scientists were looking for better ways to store an electric charge. Insulated conductors could be used to store a charge, though a more compact storage device was greatly desired.
Ewald von Kleist and Pieter van Musschenbroek, each working independently, invented a solution in the 1740s. They discovered that a glass jar lined with metal foil on both the inside and the outside was capable of holding a significant electric charge. The device came to be called a “Leyden jar” by Van Musschenbroek’s colleagues, since the Dutch scientist was at the time teaching at the University of Leiden.
Scientists continued to tinker with the Leyden jar, but its design and function remained substantially unchanged throughout its useful lifetime. Maybe the most important advancement in Leyden jar technology was the simple act of grouping several of them together. Benjamin Franklin compared this assembly to a “battery” of cannons, thereby coining the term we still use for the modern electrochemical cell batteries that power smoke alarms, flashlights, and children’s toys.
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