File:Andreas Cunaeus discovering the Leyden jar.png

English: Artist's conception of the discovery of the Leyden jar. In 1746, Andreas Cunaeus, a pupil of Pieter von Muschenbroek in Leyden, attempts to "condense" electricity in a glass of water. The rotating glass sphere (right) is an electrostatic machine. The static electricity generated by the hands rubbing on it is transferred through the chain to the suspended metal bar, and from it via the hanging wire into the glass of water. The glass acted as a capacitor, and a large charge built up in the water, and an equal charge of the opposite polarity built up in Cunaeus' hand holding the glass. When Cunaeus reached up to pull the wire out of the water, he got a severe shock, much worse than an electrostatic machine could give, because the amount of charge stored was much larger than the terminal of an electrostatic machine could store. Cunaeus took two days to recover. Musschenbroek was also impressed by the powerful shock he received from the device, writing, "I would not take a second shock for the crown of France". Reports of the experiment were widely circulated, and scientists began to investigate the charge storage ability of these "Leyden flasks". Eventually the water was replaced by foil coatings on the inside and outside of the jar to store the charge.