The Use of Chronometers to Determine Longitude on East India Company Voyages

摘要

John Arnold in his Certificates and Circumstances states that various East India Company captains used his chronometers. The earliest instance quoted is that of Captain Charles Mears on board HEICS Egmont. Captain Mears wrote to him from the Downs off Margate, concerning the use of one of his timekeepers on 6 March 1773.' His letter records the longitude using the timekeeper while anchored off the Mother Bank at the Downs with seven readings over the period 3 to 5 March. The letter meticulously records in a tabular form the correction he applies to the rate of going which was provided by John Arnold of +13 seconds gaining per day. From his tabular results enclosed in the letter, it is also clear that his use of the word 'timekeeper' means a box chronometer, as he was using a watch to transfer the time of observation to the timekeeper. This has, until now, been regarded as the first use of a chronometer by a captain on a regular commercial voyage. There is, however, evidence that Mears used a chronometer to determine longitude on an earlier voyage in 1770.