The Voltaic Pile
It was already known that the limbs of dead animals could be made to twitch by applying connected ends of wires of different materials – copper and iron – to foot and the exposed nerve. Allesandro Volta did some experiments to show that a voltage was produced and a current flowed was whenever dissimilar metals were separated by a conducting electrolyte (for the dead frog, the electrolyte was the frog's own body fluids). He constructed a pile of silver and zinc discs separated by pads soaked in salt water as shown below.
On touching the top and bottom discs he received an electric shock. Further experiments with other metals and liquids also gave electric shocks of various severity.
The pile tended to squeeze out the electrolyte and cause short circuits. Volta solved this problem by putting the discs side by side dipping into electrolyte (dilute acid).. The diagram below shows one such arrangement using zinc and copper, with copper wires.