The Observatory’s involvement with Chronometers dates back to 26 April 1766 when the Board of Longitude resolved that Harrison’s longitude watch (H4) along with his three earlier seagoing clocks should be tested there. Over the next 50 years, a small number of other chronometers were also tested mainly for the Board (these included Kendal No.1, Mudge “Green” and Mudge “Blue”).
In 1818, a new Longitude Act was passed, as a result of which, the post of Superintendent of Chronometers was created with a salary of £100 a year. Initially this was bestowed upon the Hydrographer of the Navy, Captain Thomas Hurd. On 23 July 1821 it was transferred to John Pond, the Astronomer Royal.
A month earlier, on the 25 June, following up a suggestion from the chronometer maker WJ Frodsham, the Admiralty instigated a series of annual trials at the Observatory ‘for the purpose of further encouraging the improvement of chronometers’. To encourage makers to submit their instruments, it was announced that the Admiralty would ‘purchase, at the end of each year, the chronometer which shall have kept the best time, at the price of £300, and the second best at the price of £200’.
The first trial began in 1822, and was followed by twelve others. From 1828 instead of agreeing to purchase the two best chronometers, the Admiralty instead purchased the best three for £200, £170, and £130 respectively. Each of the trials, which became known as the ‘Premium Trials’, lasted for a period of 12 months. They were discontinued in 1836 at the end of the thirteenth trial as no useful purpose seemed likely to be served by continuing them. Over the course of the trials, there had been no marked improvement after the first four trials nor had there been any new inventions or discoveries. Worse still, some individuals had abused the system by entering chronometers that they had not made.
A new series of trials in a different format was begun by Airy in 1840. In 1888/9 separate trials for watches were instigated. These trials continued in much the same format until the outbreak of war in 1914 at which point, they were suspended. Although the formal trials ceased, the testing of watches and chronometers for the Navy did not. As late as 1926, it was still the Astronomer Royal’s intention to reinstate the formal trials, but this never happened, the work of the Observatory’s Chronometer Department becoming largely confined to rating of chronometers and watches that the Admiralty already owned.
A partnership between Cambridge University Library, the National Maritime Museum (part of Royal Museums Greenwich) and the AHRC-funded Board of Longitude Project, has resulted in fully digitised versions being made available via the Cambridge Digital Archive.of the Board of Longitude papers together with associated material from the papers of Nevil Maskelyne and John Pond held in the Royal Greenwich Observatory Archives held at the University. The links below are to those papers specifically relating to the trial of chronometers at the Observatory.
Trials of Harrison’s chronometers. Observations and comparisons during the trials of John Harrison’s chronometers (H1, H2, H3 and H4) and Kendall I, with mean solar time, 1766–1767, and the rating of the Royal Observatory transit clock, 1771. The volume is comprised largely of tables of measurements, with some descriptions of how the results were achieved (RGO4/311).
Books on chronometer trials (RGO 4/312)
Nine exercise books bound together, containing the rating of chronometers and watches.
1. Comparison of Harrison 4 and Kendall I from 19 March 1770 until 15 February 1773, when Kendall I was not used. John Arnold’s watch was used as a comparison from 27 July to 13 December 1774, and Kendall I was used once more from 1 August 1775. The Harrison 4 observations end on 1 September 1775. Kendall I and III are compared for 22 April – 11 June 1776.
2. Daily rating of Thomas Mudge’s ‘Green’ and ‘Blue’ time-keepers, 21 July 1783 - 12 September 1784.
3. Daily rating of Mudge’s watch, 14 December 1774 - 26 February 1778, and comparison of Mudge’s ‘Green’ and ‘Blue’ time-keepers, 20 April 1779 – 17 July 1780.
4. Comparison of Mudge’s ‘Green’ and ‘Blue’ time-keepers, 22 June 1789 - 20 June 1790, calculated by John Crosley.
5. Rating of Coombe’s watch, 29 June 1779 – 26 January 1780.
6. Daily comparison of Mudge’s ‘Green’ and ‘Blue’ time-keepers, 21 July 1783 – 12 September 1784. The rates have been kept separate for the two watches.
7. Rates for Mudge’s first time-keeper from 14 December 1774, and kept daily from 11 November 1776 to 16 February 1778.
8. Separate daily rates of Mudge’s ‘Green’ and ‘Blue’ time-keepers, 20 April 1779 – 17 July 1780.
9. Computed variation in Mudge’s ‘Green’ and ‘Blue’ time-keepers, 24 June 1789 – 29 June 1790, with a note on how the tests were performed.
An Account of the going of Dr Maskelyne's new Chronometer N.309 made by Mr T. Earnshaw made between 1800 & 1811(RGO 4/153)
Click here for an image of the chronometer (from the Royal Museums Greenwich website)
Click here to view the Board of Longitude Papers.
Links to most of these trial results are not currently available from this website. A bound volume (ref: 10/5/995) of the published results of all 13 trials (part of the official records of the Hydrographic Department of the Admiralty, but missing some sections) is held in the Horology Office at the National Maritime Museum.
1822 Feb – 1823 Jan
1823 Mar – 1824 Feb
1824 Apr – 1825 Mar
1825 May – 1826 Apr
1826 Jun – 1827 May
1827 Jul – 1828 Jun
1828 Aug – 1829 Jul
1829 Sep – 1830 Aug
1830 Oct – 1831 Sep
1831 Nov – 1832 Oct
1832 Dec – 1833 Nov
1834 Jan – 1834 Dec
1835 Mar – 1836 Feb
The rates were published as an appendix to Greenwich Observations, (normally in the volume for the preceeding year). From 1840 to 1902/3, the instruments were described as 'Chronometers'. From 1903/4 onwards, they were described as for 'Box and Pocket Chronometers'. The dates below are the year of the trial.
The rates were published as an appendix to Greenwich Observations, (normally in the volume for the preceeding year). From 1888/9 to 1905, the instruments were described as 'Deck Watches'. From 1906 onwards, they were described as for 'Chronometer Watches'. The dates below are the year of the trial.
* cover page missing in this copy
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Except where indicated, all text and images are the copyright of Graham Dolan