Alessandro Volta builds in 1800 the first electric battery in history — the voltaic pile — by stacking alternating discs of zinc and copper separated by cloth soaked in salt water. He communicates the invention to the Royal Society of London in a letter dated 20 March 1800. The voltaic pile produces, for the first time, a continuous, controllable electric current, making possible all subsequent electrochemistry: the electrolysis of water (Nicholson and Carlisle, 1800), the isolation of sodium and potassium (Davy, 1807), and ultimately electromagnetism. The unit of electric potential difference, the volt, bears his name.