<p style='text-align: justify;'>This folder comprises manuscript notes made by Nevil Maskelyne on the workings of John Harrison's time-keeper 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>]. These were made in his capacity as a Commissioner of Longitude, while attending the 'discovery' of the principles of H4 which was made by Harrison to a select group of Commissioners and watchmakers in 1765. Such discovery was required of him by a <a href='/view/MS-RGO-00014-00001/57'> new Act (RGO 14/1:29r)</a> passed by Parliament in that year, in order to win the great reward.</p><p style='text-align: justify;'>The notes form two parts. There are three sheets of rough <a href='' onclick='store.loadPage();return false;'> notes (RGO 4/152:1-3)</a> clearly taken by Maskelyne at the discovery, which include queries made by him and Harrison's answers. One such <a href='' onclick='store.loadPage(2);return false;'> query (RGO 4/152:1v)</a> asked what changes had been made to the watch after the first trial to Jamaica. These have been numbered down one side, clearly to re-order the points for the second group of notes. This second <a href='' onclick='store.loadPage();return false;'> group (RGO 4/152:4-7)</a> comprises three sheets of fully written prose expanding the short notes. There are some rougher additions where Maskelyne seems to have been unsure of the spelling of a watch part, or has added a detail later.</p><p style='text-align: justify;'>Both sets of notes form the manuscript preparations for Maskelyne's notes on the time-keeper which introduced The Principles of Mr Harrison's Time-Keeper, with Plates of the Same published by the Board of Longitude in 1767. Much of the wording from the second group of notes, went directly into the <i>Principles</i>, but a number of details of the size and materials of parts of the watch, as well as direct references to the figures, were removed before publication. Most comments in the first group of notes were re-worked in the second, but a few were transferred directly to the <i>Principles</i>, notably a <a href='' onclick='store.loadPage(3);return false;'> comment (RGO 4/152:2r)</a> by the watchmaker Thomas Mudge on the vibration of the balance. Interestingly, a <a href='' onclick='store.loadPage(3);return false;'> comment (RGO 4/152:2r)</a> by the watchmaker William Matthews that 'it would be best to fix the Clock plates, pendulum and all to the Wall' as well as some notes by Maskelyne on how to construct this, do not reach the <i>Principles</i>. This suggests that Maskelyne verified the discussions noted at the discovery before publishing them, and may help to explain why Matthews' plan for copying the watch after the event was rejected by the Board. </p><p style='text-align: justify;'>Katy Barrett<br />History and Philosophy of Science<br />University of Cambridge<br /></p>
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