John Southern (engineer)

John Southern (c. 1758–1815) was an English engineer, son of Thomas Southern of Derbyshire.^[1] In 1796 he and his employer James Watt co-invented the Indicator, an instrument for measuring and recording the pressure inside a steam engine cylinder through its stroke.^[2] This data was crucial for assessing an engine's efficiency. Southern became a partner of the firm of Boulton & Watt in 1810.^[1] The use of the instrument was kept as a trade secret for a generation, only becoming public in the 1830s.^[3]

A Treatise upon Aerostatic Machines, 1785, by John Southern