Thomas Earnshaw, horologist, 1798.
© Science Museum / Science & Society Picture Library
Oil on canvas portrait attributed to Sir Martin Archer Shee, showing Thomas Earnshaw (1749-1829) seated at a table, with a chronometer in the background. Earnshaw was a pioneer of chronometer manufacture, and first patented a spring detent chronometer escapement in 1782, an escapement which was the standard for marine chronometers throughout the 19th century. A detent in a time piece is a catch that regulates the striking mechanism.