Based on some findings by Luigi Galvani, Alessandro Volta, a friend and fellow scientist, believed observed electrical phenomena were caused by two different metals joined by a moist intermediary. He verified this hypothesis through experiments and published the results in 1791. In 1800, Volta invented the first true battery, storing and releasing a charge through a chemical reaction instead of physically, which came to be known as the voltaic pile. The voltaic pile consisted of pairs of copper and zinc discs piled on top of each other, separated by a layer of cloth or cardboard soaked in brine (i.e., the electrolyte). Unlike the Leyden jar, the voltaic pile produced continuous electricity and stable current, and lost little charge over time when not in use, though his early models could not produce a voltage strong enough to produce sparks. He experimented with various metals and found that zinc and silver gave the best results.