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Longitude Essays

Royal Greenwich Observatory Archives > Longitude Essays

Nautical Almanac

The Nautical Almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial observations to determine the position of their ship while at sea using the lunar distance method. The Almanac specifies for each whole hour of the year the position on the Earth's surface at which the sun, moon, planets and first point of Aries are directly overhead. The positions of fifty seven selected stars are specified relative to the first point of Aries. Astronomer Royal Nevil Maskelyne suggested to the Board of Longitude that this information should be calculated beforehand for each year and published in a form accessible to navigators. This proposal was approved and under the care of Maskelyne the Nautical Almanac for 1767 was published in 1766. There is within the Barrington papers [BGN] an account of how an Act of Parliament in 1765 authorised the Commissioners of Longitude to begin publishing the Nautical Almanac. Whilst still containing general astronomical data, this was the first nautical almanac to contain data dedicated to the determination of longitude at sea. The Board of Longitude gave financial rewards to several people for their work on the Nautical Almanac, for example William Lax was given £1000 [RGO 14/46:124] in 1812 for the tables that he produced as was the widow of Tobias Mayer for the tables produced by her late husband.

In the Board of Longitude papers the Nautical Almanac is the most referenced publication. The Board spent as much money producing the Almanac as it did investigating the potential of the chronometer for solving the problem of longitude at sea. As well as the cost of printing, production and circulation, the accounts for which can be found in RGO 14/16 [RGO 14/16] and RGO 14/17 [RGO 14/17], there was also the need to pay a number of computers to work out the contents of the tables that were needed for each edition, as well as comparers to compare the work of the computers, checking it for error. These computers lived across the whole country and the Board of Longitude papers are a good record of this network. For example there is volume [RGO 4/86] which contains lunars for the year 1778 calculated by Charles Mason, an assistant at the Greenwich Observatory, along with RGO 4/84 [RGO 4/84] and 85 [RGO 4/85] which contain further work by Mason on the improvement of lunar tables. In the centre of this network of computers was Maskelyne, who organised the payment, on behalf of the Board of Longitude [REG09/000037:2:011], of the computers and comparers as well as editing together all the tables [RGO 4/288] to make a final edition. RGO 4/149 [RGO 4/149] is a volume of correspondence between Maskelyne and the computer Henry Andrews from 1768 till Maskelyne’s death in 1811. Within the Board of Longitude there are also appeals for financial charity from wives, daughters and sometimes sons of past computers and comparers. For example Margaret Mackay sent polite and very apologetic requests [RGO 14/12:326r] for assistance after the death of her husband who had worked as a computer.

In 1818 an Act of Parliament made Thomas Young Superintendent of the Nautical Almanac replacing John Pond, who had performed the role since the death of the previous Astronomer Royal Nevil Maskelyne. Young retained all correspondence [RGO 14/22] regarding improvement, reform and errata in the Nautical Almanac. Of particular significance are the letters [RGO 14/22:20] of Francis Baily and James South, both of whom attacked Young in his position as Superintendent and the administration and organisation of the Board of Longitude more generally. The content of the Nautical Almanac was actively debated in the early nineteenth century, Baily and South represented those that wanted the publication to be of more use to the astronomer, with the inclusion of additional tables. Many of the irrational schemes [RGO 14/44:83] for longitude that were sent to Young as Secretary of the Board also incorporated or suggested improvements to the Nautical Almanac.

The heavy presence of the Nautical Almanac in the papers of the Board of Longitude should serve as a reminder that the problem of finding longitude at sea was not inevitably solved by the chronometer alone. The Commissioners of Longitude held both the schemes, timekeeping and lunar distance, in high regard; furthermore both methodologies for finding longitude were used, often simultaneously, by mariners until much later in the nineteenth century.

Sophie Waring
History and Philosophy of Science
University of Cambridge