<p>This notebook was clearly a kind of astronomical scrapbook for <a href='/search?keyword=Nevil%20Maskelyne'>Nevil Maskelyne</a>, Astronomer Royal and Commissioner of Longitude, as he tackled the question of how to use the lunar distance method to find longitude at sea. It is rough, dirtied and torn, simply bound with marbled covers, its state suggesting that it accompanied him on many observations. It seems to have been part reference handbook, part notebook for rough calculations, as he includes both calculations and tables of observations, and copies of items from the <i> Philosophical Transactions </i> and the <i> Connaissances des Temps </i>, the French equivalent of the <i> Nautical Almanac </i>. Sheets with calculations and notes are pasted in between or onto pages of the notebook at regular points, some pages are written upside down, and there is even a strip of paper inserted at one point as a bookmark with a note to himself.</p> <p>Many pages are left blank, others have faint pencil calculations or single words in ink. This notebook might be compared with the similar marbled book<a href='/view/MS-RGO-00004-00150/1'>RGO 4/150</a> which contains Maskelyne's observations and calculations on his voyage to <a href='/search?keyword=St.%20Helena'>St. Helena</a> in 1762. Comparison of the two suggests that the blank pages in this book were left intentionally by Maskelyne to provide space for calculations or notes to himself that related to the observations. This is certainly what he has done in the pages that follow careful, neat tables<a href='' onclick='store.loadPage(57);return false;'>RGO 4/66:29r</a> of Jupiter's satellites for the years 1745-1760. Maskelyne subsequently added instructions on how to use these tables to find the immersions and emersions of the satellites, and details of <a href='/search?keyword=Ole%20Romer'>Ole Romer</a>'s equation of the progressive motion of light in the satellites, with a diagram. He then copied and commented on items from the <i>Philosophical Transactions</i> of 1694 and 1719 that related to the tables.</p> <p>Interesting items that have been pasted into the book include some observations<a href='' onclick='store.loadPage(87);return false;'>RGO 4/66:44r</a> of the <a href='/search?keyword=Royal%20Society'>Royal Society</a> clock at <a href='/search?keyword=Greenwich'>Greenwich</a>, which Maskelyne had taken to St Helena; and very rough, torn notes<a href='' onclick='store.loadPage(103);return false;'>RGO 4/66:51r</a> discussing the transit of Venus, which a note at the bottom explains 'were instructions that <a href='/search?keyword=Dr%20Bradley'>Dr Bradley</a> drew up at the desire of the Council of the Royal Society, relating to my observing the Transit of Venus in the East Indies. <a href='/search?keyword=C.%20Mason'>C. Mason</a>.' Maskelyne has added his own calculations on the back. There are also pages of computations<a href='' onclick='store.loadPage(150);return false;'>RGO 4/66:73r</a> of longitude by lunar distance, noted by Maskelyne as 'observed at Greenwich … with a Hadley's quadrant made by <a href='/search?keyword=Mr%20Bird'>Mr Bird</a>, by order of the Lord's of the <a href='/search?keyword=Admiralty'>Admiralty</a> to find the Longitude at Sea by the moon's distance from a star.' A touching human note is added by Maskelyne's transcription<a href='' onclick='store.loadPage(168);return false;'>RGO 4/66:82r</a> of the Latin motto on his predecessor <a href='/search?keyword=Edmond%20Halley'>Edmond Halley</a>'s tomb in Lee churchyard near Greenwich, which he notes as taken in July 1762.</p> <p>Katy Barrett<br />History and Philosophy of Science<br />University of Cambridge<br /> </p>
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