Arc lighting, c 1840s.
© Science Museum / Science & Society Picture Library
Arc lighting describes the continuous spark produced by touching the tips of two carbon rods. The mechanism that creates the light is straightforward: an electric current is pased between 2 touching rods, and the heat it generates vapourises a tiny portion of the carbon. If the rods are then pulled apart, the vapourised carbon will still carry some of the current, and in doing so produce an intense glow. Arc lighting was demonstrated by scientists such as Michael Faraday (1791-1867).