Electric egg, c 1880.
© Royal Institution / Science & Society Picture Library
In 1857, Michael Faraday (1791-1867) used an electric egg to examine electric discharges in air. The device comprises an egg-shaped glas with two metal balls inside. When the presure inside the glas was reduced to a very small value and the balls connected to a source of electricity, a luminous discharge appeared between the two balls if the voltage was high enough. Made by W Ladd (1850-1883).