<p style='text-align: justify;'>This bound volume contains nine lined exercise books in blue paper wrappers, some of which are labelled in pen. The long-serving Astronomer Royal Nevil Maskelyne and his assistants recorded in these their observations and calculations from some of the single and comparative trials of marine timekeepers or chronometers conducted at the Royal Observatory in Greenwich on behalf of the Board of Longitude during the period from 1770 to 1790. The books also include some comments on the ways in which the trials and related calculations were carried out, and by whom. The point of these trials was to establish, in combination with sea trials, whether the designs were accurate and reliable and replicable enough to be rolled out across the Naval and mercantile fleets and to garner their inventors one of the longitude rewards established in 1714. The well-known chronometer makers whose inventions were tested include John Harrison, Larcum Kendall, John Arnold and Thomas Mudge. Harrison and Mudge later vehemently accused Maskelyne of not having tried their timekeepers fairly while they were kept at Greenwich, but there is no known evidence of sabotage having been intended or carried out there.</p><p style='text-align: justify;'>The first book in the volume, which mainly deals with trials of John Harrison's design H4 [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/79142.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>], provides an example of the common contents of such records. It records comparisons of the going of 'H4' with that of Larcum Kendall's Harrison-style chronometer from 19 March 1770 until 15 February 1773, from 27 July to 13 December 1774 with John Arnold's watch instead used for comparison, and then from 1 August 1775 to 1 September 1775 with the Kendall timekeeper once more. Finally there are comparisons for Kendall's first [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/79143.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] and third [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/79216.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] designs for the period of 22 April to 11 June 1776. In 1765, the Board had directed Kendall to make a chronometer based upon the principles of Harrison's watch, and if his had proved high quality and affordable enough, he would have been put to work teaching other workmen to replicate it with an eye on larger scale production than Harrison himself could have managed. It was ready in 1770, and the Board ordered on <a href='/view/MS-RGO-00014-00005/101'> 3 March (RGO 14/5:97)</a> 'That both the abovementioned Watch Machines be delivered into the custody of the Astronomer Royal who was desired to receive the same and to make observations of their going and report the same to the next Board'. Ultimately, it was cost which prevented the Commissioners from trying to move forward with the Harrison-style design.</p><p style='text-align: justify;'>The <a href='' onclick='store.loadPage(6);return false;'> first page (RGO 4/312:1v)</a> in this record book only records the dimensions of Kendall's timekeeper, and then the second page is blank. After that, tables compare the Harrison and Kendall watches with each other and with a long-pendulum astronomical clock, in terms of their rates of going. There are occasionally notes added, as when problems required the adjustment of the timekeepers, for example when an assistant forgot to give the two chronometers their daily winding and Kendall had to come reset them <a href='' onclick='store.loadPage();return false;'>RGO 4/312:4</a>. One note was long enough to require a <a href='' onclick='store.loadPage();return false;'> separate sheet (RGO 4/312:26)</a>, inserted loose, in which Maskelyne explained the steps which he took on 1 August 1774 to try to fix Arnold's clock and to determine why it had stopped that day. Periodically, the trials would stop while one or both clocks were sent to sea or leant to Kendall for his ongoing work. All of the books in this volume follow this same basic pattern, with a brief report on the timekeepers at the beginning and end of each trial and only occasional notes interrupting the tables of observations when something atypical or disruptive occurred, or when calculations were made of the degree of error of the different timekeepers.</p><p style='text-align: justify;'>These records are important as the trials that they commemorate were a key element of the Board of Longitude's attempts to define and to procure acceptable evidence that a timekeeper was accurate and reliable enough for long-term use under maritime conditions. They were also one of the key causes of conflict between Commissioners including the Astronomer Royal and some of the best candidates from amongst the chronometer makers including John Harrison. The daily details revealed in these records also show how tricky it could be to keep the timekeepers running uneventfully even at rest in a relatively controlled environment, due to technical and human error and other obstacles - something which only became magnified once at sea, as is revealed by many of the ships' records now preserved in the RGO volumes.</p><p style='text-align: justify;'>Alexi Baker<br />History and Philosophy of Science<br />University of Cambridge<br /></p>
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