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Papers of Nevil Maskelyne : Comparison of chronometers

Papers of Nevil Maskelyne

<p style='text-align: justify;'>This rough notebook shows the results of experiments made on HMS Carcass to compare the rates of different chronometers between 30th May and 27th September 1773. Under the command of Captain Constantine Phipps (later Baron Mulgrave, a key member of the Board of Admiralty, and advisor to the Earl of Sandwich), the Carcass and Racehorse had been sent by the Admiralty to test the theory that open parts of the Arctic Ocean might allow a route to the Pacific by remaining largely free of ice. <a href='/view/MS-RGO-00014-00005/242'> Minutes (RGO 14/5:238)</a> from the Board of Longitude meeting on 24th April 1773 show the Commissioners granting Phipps whatever instruments he and the Astronomer Royal Nevil Maskelyne thought necessary for the expedition.</p><p style='text-align: justify;'>The booklet of results is made up of tables comparing the time by a number of chronometers against the mean time by observation, and a small number of entries under the heading 'Carcass' which presumably refer to dead reckoning. The time-keepers under consideration were by John Arnold, Larcum Kendall and Thomas Grignion. One column is headed simply 'watch,' presumably the time-keeper normally kept on the ship. There are regular, mostly daily entries within the May-September period, although there is some <a href='' onclick='store.loadPage(3);return false;'> confusion and changing of dates (RGO 4/154:2r)</a> around 7-10 June. The results are recorded on the recto of each page, with commentary on the verso. Mostly the tables purely contain numbers but at points small comments are adjoined such as <a href='' onclick='store.loadPage(5);return false;'> 'I imagine this should be 7' (RGO 4/154:3r)</a> or a calculation of how far a chronometer's rate was <a href='' onclick='store.loadPage(3);return false;'> 'slower than M[ean] T[ime].' (RGO 4/154:2r)</a> The <a href='' onclick='store.loadPage(6);return false;'> verso commentary (RGO 4/154:3v)</a> shows calculations for how much each watch had gained in a certain period, or recorded when a watch stopped, for how long and what affect this had.</p><p style='text-align: justify;'>There is a major gap in the observations between 5th August and 2nd September inclusive. After the gap the 'Carcass' and 'Mean Time' headings disappear. The <a href='' onclick='store.loadPage(10);return false;'> verso commentary (RGO 4/154:5v)</a> discusses the overall rate of the Arnold before the break, but there is no explanation of the gap in results. However, to test a chronometer was a complex and time-consuming process requiring setting up a tent observatory on land and time to perform observations. Given that Phipps barely managed to get his ships out of the Arctic ice, this break may mark the point at which attentions were directed away from the chronometer experiments by the hurry to survive.</p><p style='text-align: justify;'>Katy Barrett<br />History and Philosophy of Science<br />University of Cambridge<br /></p>

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