Thomas Earnshaw (1749-1829) was an eminent English watch and chronometer maker and inventor. The present watch is fitted with the spring detent escapement which he invented around 1780.
During the 19th century, this escapement became the standard for marine chronometers and continued to be manufactured for use at sea until the arrival of quartz controlled timekeepers.
For a similar chronometer by Thomas Earnshaw, numbered 626 and 3069, see The Camerer Cuss Book of Antique Watches, pp. 164 and 205.