John Theophilus Desaguliers, scientist and inventor, c 1730s.
© Science Museum / Science & Society Picture Library
Pen and wash drawing by M Seymour after an engraving. Desaguliers (1683-1744), French-born British inventor and scientist, became experimental asistant to Sir Isaac Newton. He designed a project to heat salt-boilers and similar vesels by steam rather than fire. He added a safety valve to Thomas Savery's steam engine, which along with an internal water jet, condensed the steam in the displacement chambers, improving the design.