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Longitude Essays

Board of Longitude > Longitude Essays

Isaac Newton

Isaac Newton, pre-eminent mathematician, astronomer and natural philosopher, played an important if complicated role in the development of rewards for finding longitude at sea. He read a prepared paper to a committee of the House of Commons that in June 1714 debated plans for a reward for finding maritime longitude. President of the Royal Society and author of Principia mathematica, he was taken to be the leading British authority on the determination of longitude. Several drafts of his evidence to the committee survive among his manuscripts [link] in Cambridge University Library. He listed the viable projects for determining the longitude at sea. One was proposed in 1713 by William Whiston and Humphry Ditton, involving rockets released at fixed times from ships moored at sea. Newton actively supported both men and met Ditton in March 1714. But in June he told the committee of the scheme’s difficulties since it would only help tell navigators their position near the coast. Newton also mentioned the design of a watch to keep exact time, but said such a watch had not yet been made, that two such watches would be needed, and that any watch would have to be checked against astronomical observations. Both rockets and exact clocks could keep longitude once known, not find it from scratch. Only astronomy would. He discussed timing eclipses of Jupiter’s moons, but long telescopes and ships’ movements meant this would fail at sea. Observing the Moon’s positions would work in principle, but its theory was not exact enough. Both Newton [link] and Whiston reckoned the committee’s chair, the Liverpool MP William Clayton, was opposed to the longitude bill. Nevertheless, when the Act was passed Newton’s arguments affected its terms. He insisted astronomy was required to find longitude, backed the idea that the reward’s size should match the accuracy with which the longitude could be found, and proposed rewards should be offered after trying the method on a voyage to a specified distant port.

Though he confessed he’d never been to sea, Newton had much experience with maritime longitude. He worked on the Moon’s motion from the period when he composed the Principia mathematica between 1684 and 1687, already convinced only the combination of astronomy and a good clock could find longitude at sea. Using John Flamsteed’s observations, Newton claimed he had a workable lunar theory. In 1697 Edmond Halley published a summary of Principia mathematica and its relevance to a lunar method for longitude at sea. Newton’s Cambridge manuscripts [link] include papers on the Moon’s motion of February 1700, published in English and Latin in 1702. But he never completed an exact model for lunar motions. Meanwhile, in 1699 he discussed a longitude scheme with the Admiralty secretary Josiah Burchett. At exactly the same time, Newton announced a reflecting octant to measure distance between Moon and stars at sea. Descriptions of the device survive in his Cambridge manuscripts [link] and at the Royal Society. It was eventually published in 1744, well after John Hadley had announced his own octant.

Even before the 1714 Act, Newton was lobbied by longitude claimants. After the Act, which made him one of the Commissioners, he was frequently and frustratingly involved in judging such schemes, several forwarded by Burchett. Early petitioners included a French engineer and a Hanoverian courtier. Newton read a scheme for using magnetic compasses by the mathematical practitioner John French, a proposal for a log by the Guernsey mariner Henri de Saumarez that might measure the ship’s path, and a project by John Vat that Newton dismissed [link] as just as impracticable as finding position by “burning brandy”. In drafts [link] now in his Cambridge manuscripts, he still insisted longitude could not be found by clockwork alone, and once lost could not be regained by exact watches. Many proposals reached him in the final years of his life, including those of a Coventry pamphleteer William Blundell, the Welsh physician and magnetic experimenter Zachariah Williams, and a German physician Johann Biester. In answer to the instrument maker Jacob Rowe’s scheme for a better sandglass, sent in August 1725, Newton conceded lunar theory was not yet sufficiently exact. He claimed the new Astronomer Royal Halley was already making lunar tables using Flamsteed’s data, and that reliable watches might help time astronomical observations made at sea. Newton’s longitude correspondence provides some of the few documents about the Commissioners’ activities before they first met formally in 1737. He influentially argued that [link] before the Commissioners met they should consider how astronomy might be improved “before it be applied to sea affairs”, that astronomy must first be improved on land by astronomers, not watch makers, and that the Commssioners should certainly not meet to judge any time keepers until “the instruments have been made and sufficiently tried both at land and sea and in various latitudes and witnesses are ready to attest the success”. These views affected the Commissioners’ behaviour. In the decisive year of 1765 [BGN:1:1], when lunar and chronometric methods for longitude were first discussed together, the Navy Treasurer and MP Viscount Barrington helped prepare new legislation that would seek to clarify relations with John Harrison, and ensure the continuation of the Board of Longitude. Significantly, one of his first tasks was to study the opinions that Isaac Newton had first put forward back in 1714.

Simon Schaffer
History and Philosophy of Science
University of Cambridge