Papers of Nevil Maskelyne : Lunar tables

Mason, Charles

Papers of Nevil Maskelyne

A collection of lunar tables for the year 1778. They were computed by Charles Mason, an assistant at the Royal Observatory. These tables, which predict the position of the Moon in the sky, were an important prerequisite for the production of the Nautical Almanac. This particular manuscript contains a number of notes made by Mason. As such, it helps to give an impression of the practice of computing lunar tables alongside Mason's private attitude towards the Board of Longitude.In an <a href='' onclick='store.loadPage(5);return false;'> early note (RGO 4/86:2r)</a>, Mason recounts attending a meeting with the Commissioners in which they offered him £750 for the tables. He initially refused the offer but soon changed his mind, recalling that he found his 'enemies at the Board too numerous and inflexible'. As an assistant to the Astronomer Royal, rather than a member of a learned society, Mason's social position no doubt made it difficult for him to garner support within the Board. He consoles himself with the thought that he may earn another £5000 if his tables should help improve the accuracy of the method of lunar distances to within the limits of the Longitude Act. This did not transpire, although Mason's widow was awarded another £200 for his later work. The minutes for these meetings can be found in volume <a href='/view/MS-RGO-00014-00005'> (RGO 14/5)</a> dated 28th November 1778 and 6th March 1779.Mason's other notes reveal what was left out of the Board's final publication of his tables. Whilst the manuscript includes a large number of equations, Mason puts a star symbol '*' next to those which he actually intended to present to the Board. Similarly, Mason included a greater level of detail in the manuscript calculations than in the final publication. He notes: 'I was obliged to compute these to tenths, in order to gain the nearest second. But it will appear quite superfluous to print it nearer than the second, and therefore should not be transcribed'.Towards the end of the manuscript, <a href='' onclick='store.loadPage(28);return false;'> Mason compares his calculations to the actual observations of the Moon taken by the Astronomer Royal (RGO 4/86:14r)</a>James Bradley between 13th September 1750 and 2nd November 1760. In doing so Mason taps into his experience working at the Royal Observatory. He reports when new instruments might have affected observations and on which days Bradley's journals were not complete. Such comments highlight the flip side to Mason's social position. He might have lacked institutional influence but this was made up for in practical astronomical experience. Indeed, in the 1760s Mason had been responsible for undertaking the observations used to establish the division between the states of Pennsylvania and Maryland in the USA: the eponymous Mason-Dixon line.James Poskett History and Philosophy of Science University of Cambridge