Thomas Earnshaw (4 February 1749 – 1 March 1829) was an English watchmaker who, following John Arnold's earlier work, further simplified the process of marine chronometer production, making them available to the general public.

He is also known for his improvements to the transit clock at the Royal Greenwich Observatory in London and his invention of a chronometer escapement and a form of bimetallic compensation balance.

Whilst initially the design was crude and unsuccessful, with modifications it later became the standard form in marine chronometers,[2] following the invention of the detent escapement by Pierre Le Roy in 1748.

It was highly praised by John Thomas Romney Robinson in the 19th century, who at that time believed it to be the most accurate clock in the world.

The first expedition was with HMS Bounty which had ended in the infamous mutiny led by Fletcher Christian and from which Bligh returned to England only with the greatest of difficulties.

[4] Around 1796 Earnshaw, who had temporarily lost interest in the Board of Longitude reward, was tempted back by the failure of Josiah Emery to win it.

The Earnshaw chronometer was the only one working at the end of the journey, causing Flinders to refer to it in his book A Voyage to Terra Australis as "this excellent timekeeper".

509 was carried on HMS Beagle on a voyage to circumnavigate the globe and establish, for the first time, a chain of points around the world of accurately-known longitude.