Ships, Clocks and Stars: The Quest for Longitude

In 1714 the British parliament offer an unheard-of cash prize for anyone who could succeed in calculating longitude.

John Harrison's first marine timekeeper, H1. Picture: Australian National Maritime Museum.

Belief in a flat Earth has today become ironic shorthand for any wilfully obscurantist position. Nonetheless, throughout the past two centuries, amid the triumph of science and technology, there have been obstinate attempts by some biblical fundamentalists to argue for a literal interpretation of scripture and deny the sphericity of our planet.

It might come as a surprise to such people to realise that at the zenith of Christian civilisation, in the high Middle Ages, no educated person doubted that the Earth was spherical. Dante’s whole vision of the cosmos in The Divine Comedy, composed in the very early 14th century, is predicated on the idea of the Earth as a globe around which the sun, moon and the other five known planets, and ultimately the fixed stars, ­rotate in circular orbits.

Indeed the entire system of astronomy and astrology, which was developed in the Hellenistic period and fascinated the Middle Ages, assumed sphericity and circular orbits, each of the 12 signs of the zodiac representing 30 degrees of a full circle. This model underpins the conception, entrenched for centuries in medical and psychological theory, that individuals are imprinted with certain characteristics by the position of the cosmos at the moment of their birth.

The only matter that provoked opposition from the church was the replacement of the geocentric model with the heliocentric one, although even this thesis, which opened the way to a disturbingly decentred universe, was not controversial when first proposed by Copernicus, and only the influence of Spanish arch-conservatives forced the relatively liberal pope Urban VIII to silence his friend Galileo in 1633.

The realisation that the Earth was a sphere seems to go back to Aristotle, and its dimensions were calculated in the following century by the Alexandrian astronomer and geographer Eratosthenes. Knowing that the sun was directly above Aswan at noon on the summer solstice, and measuring the shadow of an obelisk in Alexandria at the same time, he found that the sun there was slightly more than 7 degrees from being directly overhead: this meant the Earth’s circumference was about 50 times the distance from Aswan to Alexandria.

A spherical Earth incidentally raised the question of the northern and southern hemispheres and with it the idea that the latter must hold a significant continental mass to balance the African and Eurasian continents already known to the ancients. Hence one of the most intriguing aspects of the proto-history of Australia: that the existence of the southern land was postulated in theory long before Europeans set foot on it, in contrast to America, whose existence came as a complete surprise.

The ancient geographers knew of the frozen North Pole and correctly postulated a correspondingly cold South Pole, and they also knew that temperatures rose as one approached the equator. For some time there was a belief that just as the poles were too cold for human life, the equator was too hot, and thus we might never be able to cross the so-called torrid zone and determine whether there was intelligent life in the southern hemisphere.

It was probably this as much as anything else that disturbed biblical fundamentalists, since it would throw into chaos everything from the story of humanity’s descent from Adam and Eve to the idea that Christ came to redeem our sins. It was hard enough, as it was, to explain why Christ had not revealed his message to the vast majority of already known humanity.

Eratosthenes also devised the system of geographical co-ordinates that we still use, the grid of latitude and longitude that allows us to plot any position on the globe. But there was a fundamental difference between the two axes of this system, for while the equator is a natural zero degree for latitude, there is no such natural reference line for longitude. It was entirely by convention — and reflecting British maritime dominance at the time — that the zero meridian was finally set at the Royal Observatory at Greenwich.

But even after a zero meridian had been established, longitude presented a still more intractable difficulty. It was relatively easy to work out by observation of the sun and stars how far north or south you had sailed, but it was very difficult to know how far around the globe you were. We can see the result of this in early maps that often seem to show the north-south dimensions of countries more accurately than the east-west ones.

The most famous consequence of this problem was the underestimation of the westward distance between Europe and Asia that lay behind the remarkable voyage of Christopher Columbus in 1492. It was a bold adventure by any standards, but it was conceivable only because the westward distance — or the number of degrees of the circular route — was imagined as far less than it is in reality.

By a wonderful coincidence, there is an artefact that may give us some idea of what Columbus was anticipating. The earliest surviving terrestrial globe of modern times is held in the Germanisches Nationalmuseum in Nuremberg. It was made in 1492 and completed before Columbus returned in early 1493 with news of his extraordinary discovery. The distance between Europe and the Chinese coast looks roughly comparable to that between Europe and North America, and various islands, including Japan (Cipangu) are much closer.

Martin Behaim’s globe gives us a vivid idea of the state of geographical knowledge at the time, and shows it was entirely plausible to postulate a westward shortcut to Asia, even if crossing a vast tract of open ocean remained extremely dangerous. And it simultaneously makes the difficulty of estimating longitude dramatically clear.

European maritime commerce boomed in the centuries following Columbus’s voyage, dominated by the Spanish and Portuguese in the 16th century, by the Dutch in the 17th and by the British from the 18th. It was the British, now equipped with the intellectual resources of the scientific revolution and the ambitions of the burgeoning Age of Enlightenment, who decided a solution had to be found. The problem’s urgency was emphasised by terrible disaster in October 1707, when a navigational error led to the wreck of five ships on the rocky coast of the Isles of Scilly, with the loss of 2000 lives.

The story of this great intellectual adventure is told in an absorbing exhibition that comes to the Australian National Maritime Museum from the National Maritime Museum at Greenwich which, with the Royal Observatory and other historic buildings, now forms part of Royal Museums Greenwich. It effectively begins with the decision by parliament in 1714 to offer an unheard-of cash prize for anyone who would succeed in coming up with a reliable way of calculating longitude.

A board was set up to oversee the process and to consider the proposed solutions and requests for research funding; it was initially chaired by none other than Isaac Newton, one the greatest scientific geniuses of any age and the man who more than any other represented the consummation of the scientific revolution: Alexander Pope had written of him: “Nature, and nature’s laws lay hid in night / Till God said, let Newton be, and all was light.”

The exhibition deals with a number of different approaches, including more accurate and systematic measurements of the cycles of the moon and stars, observed, checked, correlated, rechecked and published by a whole scientific bureaucracy. Meanwhile the instruments of shipboard observation of heavenly bodies were made more compact and accurate. There was even an inventor who devised a mechanical means to divide degrees more accurately on sextants.

But the most effective solution seemed to lie in the measurement of time. If a mariner could know what time it was at the zero meridian when it was midday at his own location, it would be possible to work out how many degrees distant he was. The problem thus became to devise a chronometer reliable enough to keep time consistently over the months of a long sea voyage.

The hero of this story is clockmaker John Harrison, and the exhibition follows the steps of his extraordinary effort to build a clock that would withstand the tossing and pitching of a ship, the sea air and changes of temperature. The exhibition includes the unprecedentedly accurate clocks he had already begun to make before undertaking research on a marine clock, as well as reproductions of the successive designs for a reliable shipboard chronometer.

These first models, large and elaborate constructions of brass, are objects of exquisite workmanship, remarkable ingenuity and a kind of strange, metaphysical beauty, each representing years of almost inconceivable patience and determination: you imagine Har­ri­son as a man with a preternaturally slow heart rate, capable of returning day after day, month after month to perfecting his devices, shaving off margins of error of fractions of a second.

Indeed, although these are instruments to serve the needs of navigation through space, they are really time machines. And while they inevitably recall the century’s reductive mechanistic conceptions of nature and even human nature as a kind of clockwork, they also make us ponder the reality of time. It was only a couple of generations later that Kant would suggest that time was merely a category of the human mind.

It is true, in this sense, that our minds cannot experience the world except in its temporal unfolding, and yet Kant showed we are capable of conceiving that this phenomenal experience is a subjective one. And so we can see these extraordinary machines, for all their undoubted usefulness in helping us find our way through the dimensions of the phenomenal world, almost force us to question its ultimate ontological status.

These first machines were heroic efforts, but in the end Harrison changed his whole approach and decided to work on a much smaller scale: it was in the end a kind of greatly enlarged pocket watch, known as H4, that proved to be the most reliable chronometer, and it was a replica of this that Cook carried with him on his second voyage.

Captain Bligh had one on the Bounty too in 1789, although the mutineers kept it when they put him and 18 loyal crewmen on a launch.

With only a quadrant, known since antiquity, and a compass, invented in the Middle Ages, Bligh navigated for 6700km and 47 days to reach Timor. Machines may be an invaluable aid, but in the elusive dimensions of time and space, nothing can replace a sense of direction.

Ships, Clocks and Stars: The Quest for Longitude

National Maritime Museum, Sydney. Until October 30.