TIME AND OCEAN STUDY
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- A replica of John Harrison’s first marine timekeeper, H1, on show at the National Maritime Museum; Harrison’s marine timekeeper H4 (1759), right; Larcum Kendall’s marine timekeeper K2 (1771) bottom right 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