Six's self-registering thermometer, 18th century.
© Science Museum / Science & Society Picture Library
James Six (1731-1793) retired early from busines to devote himself to the natural sciences. He is best known for the invention of the self-registering thermometer, first designed in 1780, which recorded the maximum and minimum temperatures reached. It was the most widely used thermometer for taking deep-sea temperatures until 1870. The thermometer's susceptibility to presure was addresed in 1869 by Dr W A Miller (1817-1870), then Vice-President of the Royal Society. Miller's adaptation of Six's design was made by the instrument maker L P Casella (1812-1897).