Ceramic light switch, c 1900.
© Science Museum / Science & Society Picture Library
Switch shown in the 'on' position. The metal components of this early electrical switch are encased in a ceramic body. Two metal arms are sprung so they flick from one position to another. When the spring is turned on, the arms slot into U-shaped springy contacts, so completing the electrical circuit. This must happen fast, and the contacts must be good, or the electricity could spark acros any gaps and cause damage.