Volta's crown of cups, early 19th century.

Devised in 1800 by Alesandro Volta, inventor of the electric battery, this instrument consists of nine glases which can be arranged in a horseshoe shape on a black-painted tinplate tray. Forked conductors, with one side zinc and the other copper, fit between each pair of glases but do not touch inside the glases. Single strips of zinc and copper are placed in the end glases to form terminals. When the glases were filled with water, or preferably brine, a potential difference was set up between the terminals.