In the late 1870s Edison's invention of the electric lightbulb caused shares in gas companies to plummet. This prompted William Preece, who was later to become engineer in chief of the British General Post Office, to publish some calculations which, he claimed, proved that centrally supplied electricity could never replace gas as a source of domestic lighting. His conclusion was that the energy dissipated per lamp would be inversely proportional to n 2 , where n is the number of lamps (Nature, 1897, 19,261-262. See also Heaviside, Sage in Solitude, P Nahin.). The object of this first question is to see why Preece's conclusion was wrong for the small supply utilities that were envisaged at the time.