Anyone who has read Dava Sobel’s wildly successful Longitude might well get the impression that after the down trodden hero (Harrison) had finally defeated the forces of evil (Maskelyne, The Longitude Board, The Admiralty etc.) that all was hunky dory and in future the British sailors could sail the Seven Seas with the certain knowledge that they knew where they were. In reality this was far from being the case. The successful trials of Harrison’s H4 were not the end of the story but rather the beginning for a number of very good reasons. Basically Harrison’s chronometer was too complex and too expensive. It would be quite a long time before other watchmakers had simplified the marine chronometer and made its manufacture cheap enough so that all ships navigators could or would make this their principle means of determining longitude.
The English watchmaker Thomas Earnshaw who was born on the 4th February 1749, was one of those who made a substantial contribution to the evolution of the marine chronometer. Earnshaw further developed a simpler and more accurate escapement mechanism that had been invented by another English watchmaker, John Arnold (1736 – 1799). The Arnold/Earnshaw chronometers were considerably simpler than Harrison’s but were consistently accurate and mechanically reliable. In 1805 the Board of Longitude awarded Earnshaw £2500 and Arnold’s son £1672.