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Papers of Nevil Maskelyne : Rating of longitude watches on HMS Adventure

Bayly, William

Papers of Nevil Maskelyne

<p style='text-align: justify;'>An account of the rate of going of the two John Arnold timekeepers that had been issued to travel with the astronomer William Bayly on board HMS Adventure as part of what is known as Captain Cook's second voyage that lasted from 1772-1775. The Adventure, under the command of Tobias Furneaux was one of two ships equipped for this voyage, the other being HMS Resolution commanded by Captain Cook. The general purpose of this voyage was to explore the South Pacific to determine the location and existence of what was called 'Terra Australis Incognita' - that uncharted southern land mass, argued by many, including the first Hydrographer of the British Admiralty Alexander Dalrymple, to have existed. Missions like this from the late 1760s, however, began to involve a new type of personal - specially assigned astronomers, equipped with a range of instruments and detailed instructions for testing expensive technologies, making laborious astronomical observations and calculations, and making sure the instruments (typically owned by the Board of Longitude or the Admiralty) were not broken or stolen. Joining the voyage was another astronomer, William Wales, who travelled with a similar package of instruments to William Bayly and who also carried two timekeepers - one by Larcum Kendall and another by John Arnold.</p><p style='text-align: justify;'>This document gives no account of the going of the timekeepers entrusted to Bayly at sea. It does however, indicate the range of procedures developed in order to try and create an environment and context from which some sense of how a particular timekeeper had performed at sea. It should be remembered that in this period - and indeed for several decades to come - the idea of how timekeepers would be part of a practicable solution to finding Longitude at sea was still very much uncertain. We see from this document that before the voyage, the Astronomer Royal Nevil Maskelyne had tried the timekeepers at the Royal Observatory to determine their 'rate' - the amount of time that a timekeeper gained or lost per day. This procedure was absolutely necessary to using a timekeeper as it was always the case that a mechanical timepiece would lose or gain time. The difference, in theory, between a good timekeeper and poor one for finding Longitude, was whether the timekeeper kept a steady rate of losing or gaining or not. However, as shown in this document, even as the voyage began, many other factors could influence the rate of going of a timekeeper. Bayly notes on this <a href='' onclick='store.loadPage();return false;'> page (RGO 4/322: 1)</a> that on 12 July 1772, when the Adventure was at Plymouth, he found that the watch No. 2 had stopped. In order to rectify this, he says he got it going again 'by giving it a circular motion to make the balance vibrate'. Such acts of very physical maintenance were joined by what has been called 'metaphorical maintenance', in which an unusual going of a timekeeper was explained through an explanation not relating directly to the specific material environment. Such acts of physical and metaphorical repair were absolutely crucial for the trialling and use of timekeepers at sea, and it within this system that I believe we should understand this document, and indeed the role of astronomer at sea in the late eighteenth and early nineteenth centuries.</p><p style='text-align: justify;'>Eóin Phillips<br />History and Philosophy of Science<br />University of Cambridge<br /></p>

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