John Theophilus Desaguliers, French-born scientist and inventor, 1725.
© Science Museum / Science & Society Picture Library
Engraving by P Pelham after an original painting by H Hysing. Desaguliers (1683-1744), a 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. He appears here holding a magnifying glas, with a glas prism on the table.