<p style='text-align: justify;'>This collection of miscellaneous papers includes a draft letter written by Nevil Maskelyne from Barbados to the Board of Longitude. It is undated but presumably became the letter that was noted by the Board in their <a href='/view/MS-RGO-00014-00005/66'> meeting (RGO 14/5:62)</a> of 18th September 1764 as having been sent on the previous 22nd December. The minutes of this meeting note only <a href='/view/MS-RGO-00014-00005/67'> that (RGO 14/5:63)</a> a letter with Maskelyne's observations had been received, and <a href='/view/MS-RGO-00014-00005/71'> that (RGO 14/5:67)</a> this also contained his negative opinion regarding the marine chair invented by Christopher Irwin. The multiple crossings out and corrections on this draft, however, show that these communications were by no means unproblematic.</p><p style='text-align: justify;'>The letter makes explicit the complicated process undertaken by Maskelyne in order to fulfil his instructions from the Board (given to him at the <a href='/view/MS-RGO-00014-00005/61'> Board meeting (RGO 14/5:57)</a> on 9th August 1763) to trial both the lunar distance tables of Tobias Mayer and Irwin's chair on his voyage to Barbados, and to establish the longitude of Barbados while there by constructing an observatory. At the time of Maskelyne's writing, the observatory was almost finished and ready for the clock and equal altitude instrument to be installed. Maskelyne discussed the propitious location found for the observatory on Constitution Hill, the size and set-up of the structure, and how the roof shutters would allow him to make observations more accurately. He explained that the instruments had in the meantime been housed at Willoughby Fort and used there for observations, but that being in the open air had affected the accuracy of these results. The last page of the letter includes a detailed timeline of his voyage and some preliminary results. The full set would be published in 1764 as <i>Astronomical observations made at the island of Barbados; at Willoughby Fort; and at the Observatory on Constitution Hill, Both adjoining to Bridge Town</i> .</p><p style='text-align: justify;'>More particularly, Maskelyne discussed in detail his attempts to make observations onboard the Princess Louisa while using Irwin's marine chair, concluding that he had found it totally useless. He listed eight different opportunities he had had of calm weather to make observations on the voyage, and that he was only once able to observe Jupiter's satellites and that this was without using the chair. He therefore concluded that '<a href='' onclick='store.loadPage(28);return false;'> Mr. Irwin's marine chair affords no convenience or advantage to an observer in using a telescope for observing the celestial phenomena at sea, but rather the contrary (RGO 4/320:7:2v)</a>.' He subsequently justified his decision to make observations without the chair for the latter half of the voyage, partly in order better to test the Hadley's sextant he had been given to trial the lunar distance method. He also explained his method of allowing for errors in this instrument, and the affect of the climate.</p><p style='text-align: justify;'>Most interesting, is the awareness that Maskelyne showed in his letter, and which is not considered in the minutes, of his '<a href='' onclick='store.loadPage(27);return false;'> delicate (RGO 4/320:7:2r)</a>' position as regards testing the marine chair. He pointed out that his criticisms of the chair could be used by Irwin and his friends to criticise Maskelyne's own observing skills, and that he was therefore in danger of falling foul of public opinion. We can join these concerns to the questions, recorded in the manuscript ' <i>Harrison Journal</i>' which William Harrison also posed on his later arrival at Barbados. He queried the appropriateness of Maskelyne taking the observations to test 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>], given Maskelyne's supposed allegiance to the lunar distance method; and recorded Maskelyne's subsequent confusion and the effect of this on the accuracy of his observations. It seems Maskelyne was right to feel the '<a href='' onclick='store.loadPage(27);return false;'> weight (RGO 4/320:7:2r)</a>' of the honour given him by the Board of Longitude in carrying out these trials.</p><p style='text-align: justify;'>Katy Barrett<br />History and Philosophy of Science<br />University of Cambridge<br /></p>
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