William Preece. Historical portrait of the Welsh electrical engineer Sir William Henry Preece (1834-1913). Preece was trained by Faraday at the Royal Institution. From 1853 Preece worked for a number of telegraph companies and in 1870 he joined the Post Office, becoming Chief Engineer in 1892. His main work at this time was pioneering telegraphy and railway signalling. With Fleming, Preece showed that a thermionic current flowed between a hot filament and a cold conductor in an incandescent lamp. Preece also discovered electrical inductance between two parallel wires. From 1892 he worked in radio and encouraged Marconi to do his early radio experiments.