William Hedley

William Hedley (1779–1843) was an English colliery viewer and engineer at Wylam Colliery west of Newcastle who, with enginewright Jonathan Forster and blacksmith Timothy Hackworth, designed and built Puffing Billy and Wylam Dilly in 1813–14 — the oldest surviving steam locomotives in the world — and who conducted the crucial experiments that settled a fundamental question in early locomotive engineering: whether smooth-rim wheels on smooth rails could provide sufficient adhesion to haul a useful load without the aid of rack-and-pinion mechanisms.

Born at Newburn-on-Tyne on 13 July 1779, Hedley was appointed viewer — the practical engineering manager — of Wylam Colliery in 1805. The colliery's horse-worked tramroad was struggling to handle its coal output, and the possibility of steam traction was attractive, but many engineers doubted that a smooth-wheeled locomotive could grip smooth iron rails firmly enough to haul a loaded train. Hedley addressed this question systematically, building a test vehicle pushed along the rails by men turning handles to determine how much force the wheels could develop before slipping — an early scientific experiment in railway traction mechanics that conclusively demonstrated adequate adhesion for useful haulage.

This result made the Blenkinsop rack-rail system unnecessary, and Hedley's team proceeded to build the smooth-wheel adhesion locomotives that proved the principle in commercial service. Puffing Billy, completed in 1813–14, worked the Wylam Colliery waggonway for nearly fifty years before being retired and preserved. It is now displayed at the Science Museum in London as the world's oldest intact steam locomotive. Wylam Dilly, its companion, is at the National Museum of Scotland in Edinburgh. Hedley died at Newburn House on 9 January 1843.