The Longitude Problem — Reading

Passage

A Latitude has never been especially difficult. A sailor who measures the angle of the sun at noon, or of the pole star at night, can work out how far north or south of the equator the ship lies. Longitude is another matter entirely. Because the Earth turns, east-west position is not written on the sky in any fixed way. It can only be deduced by comparing the local time, which the sun supplies, with the time at some agreed reference place. Every hour of difference corresponds to fifteen degrees of longitude. The problem, for most of the age of sail, was that no ship carried a reliable way of knowing what time it was somewhere else. B The consequences were not academic. Vessels routinely made landfall hundreds of kilometres from where their officers believed themselves to be, and provisioning was guesswork. The disaster that finally forced official action came in 1707, when a British fleet returning from Gibraltar struck the Isles of Scilly in fog. Four ships were lost and around two thousand men drowned. The navigational error was in longitude. Seven years later Parliament passed the Longitude Act, offering a prize of twenty thousand pounds — a fortune — for a method of determining longitude at sea to within half a degree. C Two approaches competed. The astronomical method treated the sky itself as a clock. The moon moves against the background stars at a predictable rate, so measuring the angle between the moon and a chosen star gives, with enough tables and enough arithmetic, the time at Greenwich. These 'lunar distances' had the great advantage of requiring nothing that could break. They also required clear skies, a skilled observer, and roughly four hours of calculation for a single fix. D The mechanical method was simpler to describe and far harder to build: carry a clock set to Greenwich time. Isaac Newton had dismissed the idea, and his reasoning was sound. A pendulum is useless on a moving deck. Metal springs and balances expand and contract with heat, gain and lose with humidity, and a ship supplies all of these in abundance along with constant motion. No clock then in existence kept time well enough on land, let alone at sea. E John Harrison was a Lincolnshire carpenter with no formal training in horology. Between 1730 and 1760 he built a succession of marine timekeepers, each abandoning more of the assumptions of the previous one. His early machines used counter-oscillating beams linked by springs, so that the motion of the ship affected both equally and cancelled out, and bimetallic strips that compensated automatically for temperature. His fourth attempt looked nothing like the others. H4 was a large watch, roughly thirteen centimetres across. On a voyage to Jamaica in 1761 it lost about five seconds in eighty-one days. F The prize was not paid. The Board of Longitude, whose membership leaned heavily towards astronomers, demanded a second trial, then demanded the mechanism be explained and copied, then demanded further proof. Harrison was in his seventies before he received substantial payment, and then only after appealing directly to the king. Historians still disagree about how much of this reflected genuine scientific caution — a single successful voyage is not proof of reliability — and how much reflected a committee reluctant to award its prize to an untrained provincial carpenter over the astronomical method it had expected to win. G In practice both methods were used together for decades. Chronometers remained expensive, and a navigator who could take lunars had a way of checking a clock that might be drifting. Only when mass production brought the price of a marine chronometer within reach of ordinary merchant vessels did the astronomical method fade. The problem was, in the end, solved twice. H The Board of Longitude's conduct toward the clockmaker John Harrison, whose chronometers eventually proved the more practical solution, remains a case study cited in discussions of institutional bias in scientific and technical prizes generally. Harrison, a self-taught carpenter and clockmaker with no formal scientific standing, spent decades refining a sequence of increasingly accurate marine timekeepers, each significantly more reliable than the last, while board members with backgrounds in astronomy — the discipline behind the rival lunar-distance method — repeatedly raised the bar for what would count as sufficient proof, in ways Harrison's supporters characterised at the time, and many historians have agreed since, as reflecting a preference for the academically respectable solution over the practically superior one. Harrison eventually received a substantial portion of the prize money, though only after direct intervention from King George III and years past the point at which his fourth chronometer had already demonstrated accuracy well within the board's own published standard. The episode is now commonly invoked well beyond the history of navigation, as an illustration of how institutions charged with evaluating innovation can be slow to recognise a solution that arrives from outside the credentialed community they expected it from.