1714 - The Longitude Act

The Longitude Act is passed by the Parliament ‘for providing a Publick Reward for such Person or Persons as shall discover the longitude at Sea’. A Board of Longitude is established. It is composed of twenty-four high rank characters, seafarers and scholars. It will assess worth of the contributions claiming some reward.

The promised reward amounts to £20,000 – a hundred years of captain’s wages – to the one or ones who would supply the elements, whatever their nature, intellectual or physical, so as to achieve accurate landings. The criterion is to deliver a longitude false by less than half a degree – that is 28½ miles at Kingston, Jamaica – after crossing the Atlantic ocean to the West Indies. Meanwhile, the Board may intervene under the form of lesser but stimulating rewards, up to £2,000, for significant steps forward.

¤ What do such amounts compare to ? The Chancellor of the Exchequer earns £5,000 a year, the Surveyor of the Navy £500, a captain £200, a seafarer between £5 and £20, a specialist like a carpenter between £20 and £40. In London, the basic 4-pound loaf costs 6 pence on average – that is £9 or £10 for day-to-day bread over a year.

This decision stems from a petition that came to Westminster lately. Signed by ‘Captains of Her Majesty’s Ships, Merchants of London, and Commanders of Merchant Ships’, it summoned the government to pay attention to the longitude problem, deemed as responsible of tens or hundreds of shipwrecks.

There is no exaggeration, alas, even if there are many other ways of sinking. The late loss of warships on the Scilly’s reefs in 1707 had stressed the question, assigned by the public to a false longitude although the real issues were a likely error in latitude combined with an inaccurate bearing and some neglected drift.

¤ The Admiralty refrains from contradicting. The longitude version is politically correct, contrary to the real causes of the wreckage. It withholds a set of issues about navigation procedures.

Questioned by the Parliament, Isaac Newton has named two possible methods to settle the question of time – i.e. knowing time precisely aboard the ships – which underlies the question of longitude : either by a very accurate watch, or by measuring the angle between the moon and the sun at daylight, or between the moon and a star at night. The latter method of determining time was imagined in 1524 by Vernerus, Johannes Werner (†1522), a priest, a mathematician and an astronomer. Both methods require elements which are still lacking at the appropriate level of accuracy nowadays : there is neither steady watch nor reference of moon position through time in the form of precise lunar tables yet. Moon motion displays irregularities which outwit simple usage of Newton's law of gravitation

¤ To achieve a half-a-degree accuracy for landing on the other side of Atlantic ocean, a watch must not loose time by more than two minutes on the journey, that is three seconds a day for a 40-day journey, which is a standard performance for a warship to cross the Atlantic ocean, two seconds for a 60-day journey, which is standard performance for a merchant vessel.

As we all know, the question of longitude is closely related to the question of time. If the sailors could precisely know time at the prime meridian when they observe sun culmination, that is local noon, they could deduce the time difference between the meridian where they currently sail and the prime one, hence longitude in terms of time. The problem is : there is nothing aboard a ship which can give time today.

¤ An hour corresponds to 15 degrees of longitude, a minute of time to 15 minutes of longitude. A minute of longitude is an arc of a parallel, the length of which varies with the cosine of the latitude of said parallel : one mile of 6,076 feet on the Equator, 918/1000th of a mile on a Tropic, 707/1000th of a mile by 45 degrees of latitude – e.g. Bordeaux –, half a mile by 60 degrees of latitude – e.g. Oslo – and zero at the Pole.

Curiously, nobody raises the question of the best possible usage of £20,000. The idea of a reward meets public agreement, which has been the real Parliament’s goal if you allow this perfidious thought. But this sum could pay about thirty astronomers during ten years – an effort that should bring the required lunar tables for sure and other tips with. But the investment would not show off the same appearance of gleaming altruism as the reward.

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IN RETROSPECT FROM TODAY

NOTE A - About Newton’s opinion.

Newton believes that accurate lunar tables could be established within a few years. He is right but nobody will endeavour to achieve it before a generation. Besides he thinks that the accurate watch is a remote dream. He nevertheless mentions the two possibilities.

NOTE B - About the implementation of Newton’s axes of research.

He would have been be surprised that the seafarers must wait until 1752 to get accurate Tobias Mayer’s Lunar Tables, and until 1767 to see them incorporated in the form of pre-tabulated data by Astronomer Nevil Maskelyne in the Nautical Almanac – and in 1774 by Joseph-Jérôme Lefrançois de Lalande in the Connoissance des Temps. Mayer works alone which proves that an affordable effort in astronomy and mathematics would have solved the question without waiting for forty years.

The motion of the moon induces a correspondence between Mayer and Leonhard Euler (1751-55), which made Euler re-think the trajectory of the moon as a three-body problem, for which he found an approximate solution and exposed in his Theoria motus lunae exhibens omnes ejus inaequalitates (1753). (Note that Alexis Clairaut (†1765) had already delivered an approximate solution for the three-body system and published a Théorie de la Lune (1752) as a result.)

Mayer's widow was awarded £3,000 and Euler £300, as the board of Longitude believed that Euler oriented Mayer's work, whereas it seems to be the opposite, observations giving some food for thinking.

NOTE C - About the Board of Longitude

It does not meet before 1737 and the first results of John Harrison's maritime watch H1. It awards him £500 to finance further improvements. Globally Harrison will be awarded £5,000 over the years, from a proposition to the other.

The Board will be abolished in 1828. At that time the lunar-distance method has been established and widely used for more than fifty years, while the maritime watch is diffusing.

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SUGGESTED BIBLIOGRAPHY

Eva Germaine Taylor – The Haven-Finding Art, a History of Navigation from Odysseus to Captain Cook – London, 1958

Dava Sobel – Longitude : The True Story of a Lone Genius Who solved the Greatest Scientific Problem of his Time – New York, 1995

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CREDIT

Godfrey Kneller - Portrait of Isaac Newton - oil on canvas, 1702 - © National Portrait Gallery