The first capacitor was a jar of water that delivered a brutal shock
In October 1745, Ewald Georg von Kleist ran a wire from an electrostatic generator into water held in a glass jar. When he touched the wire, the jolt was far worse than anything the machine produced alone. He had stored electric charge, building the ancestor of a component now inside nearly every electronic device.
A year later the Dutch physicist Pieter van Musschenbroek built a similar device at Leiden, and it became known as the Leyden jar. He was so rattled by the jolt that he wrote he would not take a second one even in exchange for the whole kingdom of France. Soon Daniel Gralath linked several jars together to hold more charge, and Benjamin Franklin showed that the charge sat on the glass itself, not in the water. Franklin borrowed a military word for a row of jars, battery, which later passed to chemical cells. Early electricians even measured capacitance in jars, one being roughly 1.11 nanofarads.
The principle has barely changed. Two conductors sit close together, separated by an insulator called a dielectric, such as glass, mica, paper or plastic film. Apply a voltage and positive charge gathers on one side and negative on the other, with no current crossing the gap. A useful comparison is a stretchy diaphragm across a water pipe: water cannot pass, but the membrane bulges and springs back, storing energy, and bursts if pushed too hard, just as a dielectric can break down.
Radio drove the next wave of design around 1900, demanding compact, standardised parts. Paper capacitors rolled into cylinders appeared from 1876, William Dubilier invented mica versions in 1909, and Charles Pollak patented an aluminium electrolytic type in 1896. In 1957 H. Becker patented a porous-carbon capacitor with enormous capacity, frankly admitting he did not know exactly how it worked; its descendants are today's supercapacitors.
Nature builds giant capacitors too: clouds and the ground, with air in between, store charge until the air gives way as lightning. Inside computers, tiny capacitors hold bits of memory, an arrangement Robert Dennard turned into modern DRAM in 1966 by pairing each one with a single transistor.
Source: Capacitor
