<p style='text-align: justify;'>This volume gives an impression of the problems faced in developing and testing reliable chronometers during the later period of the Board of Longitude's existence. The majority of this correspondence relates to the period between 1811 and 1828, although there are also some miscellaneous items from the 1790s.</p><p style='text-align: justify;'>Correspondents continue to address the effects of variation in air temperature, revealing the persistence of this basic problem well after the trials of John Harrison [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/136321.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>]'s timepieces in the eighteenth century. In 1814, for instance, Robert Gillepsie<a href='' onclick='store.loadPage();return false;'> writes (RGO 14/24:299)</a> from Leith suggesting that navigators should surround their chronometers with ice in order to preserve a constant temperature. He also compares poppy oil against olive oil for use as a lubricant in the context of this problem.</p><p style='text-align: justify;'>Despite these familiar issues, the early nineteenth century also introduced new demands. The upkeep of marine chronometers, given their increased use, became a more pressing concern. It was all very well possessing a highly accurate chronometer, but this was no good if it broke half way round the Cape of Good Hope, a theme Simon Schaffer has described in his work on “states of disrepair”. Indeed, in 1812 a watchmaker based in London, Samuel Grimaldi, <a href='' onclick='store.loadPage();return false;'> wrote to the Board (RGO 14/24:271)</a> describing in detail a number of common causes of such malfunction. The “accidents” he lists include the breaking of the main chain, something he attributed to deficient elasticity in the main spring. He then goes on to market his own chronometer, which did not include a main spring, as “more durable” than his competitors.</p><p style='text-align: justify;'>Broken chronometers were not just a problem faced by navigators; they also affected the testing of new timepieces at the Royal Observatory in Greenwich. In 1824James Scrymgeour sent his chronometer from Glasgow to Greenwich for trial. However, he soon received a letter back explaining that it had been found much more variable than he had indicated. Scrymgeour went on to complain that <a href='' onclick='store.loadPage();return false;'> “it must have got some some injury in the carriage” (RGO 14/24:419)</a>. Such problems of transit no doubt contributed to the convergence of clockmakers on London during this period.</p><p style='text-align: justify;'>As Scrymgeour's letter indicates, trialling chronometers at Greenwich was a laborious process. Not only did the clockmaker need to deliver the timepiece to the Royal Observatory intact, but they also had to wait months for trials to be completed. After having waited several months for a verdict on own timepiece, Grimaldi complained that it was “impossible for any man except possessed of property ever to succeed”. The numerous pages of tables describing the trial of Thomas Cumming's chronometer between 1819 and 1820 are a testament to this fact. However, these tables also indicate the labour that went into such trials on the side of the Board. Notes indicate the chronometer often needed cleaning and <a href='' onclick='store.loadPage();return false;'> one entry (RGO 14/24:361)</a> of 30th April 1820 reads “Taken ill this morning & forgot to wind it up”. As with machines, humans were equally liable to fall into “states of disrepair”.</p><p style='text-align: justify;'>James Poskett<br />History and Philosophy of Science<br />University of Cambridge<br /></p>
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