Эндрю Тэйлор – The World of Gerard Mercator: The Mapmaker Who Revolutionised Geography (страница 3)

The merchants brought wealth to Alexandria as well. In the days of its greatness, the story went, the buildings contained so much glistening marble that a tailor could thread his needle by the reflected light of the Moon. The library where Ptolemy worked, with its collection of some seven hundred thousand manuscripts in Hebrew, Greek, and Egyptian, was one of the most obvious expressions of that wealth. Just as the merchants in the port haggled and bargained over the commerce of the mightiest empire the world had ever seen, so Alexandria’s scholars swapped ideas and theories in the library and the museum associated with it.

There are no surviving original manuscripts of Ptolemy’s work, and hardly any facts known about his life, but it would be hard to exaggerate the effect of his books on the generations that followed him. For centuries after his death, they were largely forgotten in the West, but to Mercator, the writings of Ptolemy represented the fount of ancient knowledge, the standard by which new discoveries and theories should be measured. Apart from the eight books of the Geographia, the Almagest set out Ptolemy’s views on astronomy and the place of the Earth at the center of the universe, while his various other writings encompassed mathematics, music, and history.

Other writers had concentrated on stories of the wonders that lay at the farthest reaches of knowledge, but Ptolemy’s main interest lay in establishing a reliable and coherent system for showing the spherical Earth on a flat sheet of paper. Philosophers could only suggest what form the Earth took, while travelers either by land or by sea could do little more than estimate distances – in both cases, their contributions were merely elegant guesswork. The generally accepted image of the land surrounded and limited by the ebbing and flowing waters of the sea suggested a comfortingly finite world. Ptolemy raised the possibility of a world beyond those boundaries, basing his conclusions not just on the arguments of the philosophers and on the reports of travelers but also on exact astronomical measurements.

Ptolemy saw geography as a mathematical enterprise, a matter of measurement and calculation rather than the simple telling of stories. Like Mercator some fourteen centuries after him, he designed and made instruments for measuring angles and altitudes in the heavens; his Geographia includes descriptions of a brass astrolabe and a quadrant for calculating the height of the Sun in the sky.

Ptolemy knew the true location of a place could be fixed by taking precise sightings of the stars. The Geographia therefore included a catalog of some eight thousand place-names, rivers, mountains, and peninsulas, each of them with its position defined by degrees of latitude and longitude. It is a work of staggering ambition and exactitude – the first time anyone had attempted to use coordinates in such a precise way. Many of the observations Ptolemy needed to make the calculations had already been taken, but to place cities in remote or unexplored parts of the world, he had no choice but to rely on traditional accounts and the estimates of travelers. In such a case, he said, the mapmaker should use his judgment as to what figures to use, “deciding what is credible and what is incredible.”⁴

It is impossible to know whether Ptolemy drew any maps to go with his Geographia. The illustrations that adorned medieval versions of his books were additions by later copyists working to his descriptions and coordinates, but in them his worldview, with the traditional three continents of Europe, Asia, and part of Africa, can clearly be recognized. Taprobane is grotesquely out of proportion in comparison with the half-formed India that lies to its north, and the coastline of the Far East is clearly drawn largely from imagination, but the Arabian peninsula and the whole of the Mediterranean basin are presented in some detail.

Perhaps most important of all, though, Ptolemy left open the possibility that there were more lands to be discovered beyond the extent of his own knowledge. Where the Romans and Greeks who came before him had been content to keep their studies inside the limits of the habitable world, his interest was in the Earth as a whole, and geography, for him, was no more or less than the art of making maps. “It is the prerogative of Geography,” he said, “to show the known habitable earth as a unit in itself, how it is situated and what is its nature; and it deals with those features likely to be mentioned in a general description of the earth, such as larger towns and great cities, the mountain ranges and the principal rivers.”⁵

The circle of seas that surrounded the Earth in the early T-O maps was one way of suggesting a round world, but Ptolemy’s was the first serious attempt to deal with the problem of projection. He described two possible solutions, based on a simple rectangular grid that ancient Greek philosophers had already devised, but adapting it to take account of the fact that the Earth was curved, not flat.* The systems he suggested were, as they had to be, a compromise, and one which worked satisfactorily enough within the limits of the known world. Even in the sixteenth century, most maps were still produced on grids that were simple adaptations of Ptolemy’s projections. Mercator’s greatest achievement would lie in rethinking these fifteen-hundred-year-old proposals.

Ptolemy’s geographic writings are filled with errors of fact, many of them, as he engagingly admitted himself, due to a lack of basic information. Some, such as the “great southern continent” that he believed must balance the world on its axis, would endure, like the fabulous creatures described by Herodotus and other Greek writers, for centuries after Mercator.

For all its shortcomings, though, the rediscovery and publication of the Geographia in the West laid the foundations for the work of the great cartographers of the sixteenth century. The book traveled with Columbus to the New World; when Mercator compiled his great world map of 1569, he began with Ptolemy’s calculation of the position of Alexandria. The Geographia was still being treated as the ultimate authority fourteen hundred years after its author’s death. It shows a man trying to apply scientific methods to achieve a precise, objective representation of the world in a way that was unique in his time, and remained so until Mercator’s day.

IN THE EAST, the scanty records and remains of the work of the Chinese suggest that they had their own impressive tradition. Around the third century AD, a government minister of works named Phei Hsiu set out official principles for the making of maps under the Chin Dynasty. The most important of these was that they should be constructed on a rectangular grid in order to create a consistent scale and locate places accurately. There is no evidence that Ptolemy’s thinking had reached the Far East – a grid system had been introduced in China some two hundred years before Phei Hsiu by Ptolemy’s near-contemporary Chang Heng, an astronomer royal of the Han Dynasty.* He wrote of a spherical world suspended in infinity, like a yolk in an egg, and the system he introduced of building up a map by equal squares – “casting a net over the Earth,” in a contemporary phrase – was the basis of Chinese cartography for centuries.

Chang Heng’s grid made no allowance for the curvature of the Earth, and it is hard to know from what is left of ancient Eastern cartography whether his image of a spherical world had any effect on current thought. There are no indications that early Chinese mapmakers realized the world was a sphere, that the lands they were mapping were consequently curved, nor whether the challenge, which still fascinates cartographers, of representing such a three-dimensional world on a flat surface had even occurred to them as a problem.

In the Islamic world, Arab mapmakers drew on the ideas of Ptolemy and the Greeks to develop their own traditions. By the eighth century, they were compiling maps for overland diplomatic missions to China, military campaigns, and trading expeditions; the tales of Sindbad the Sailor, dating from some two hundred years earlier, are ample evidence of their seafaring traditions. Unlike the work produced by medieval monks in Europe, their maps seem to have been designed for use as much as for study, but they were still based mainly on copies of older European originals. There are early versions of the T-O maps, with south at the top and Mount Sinai in the center and, slightly later, more distinctively Arab interpretations in which a disk-shaped world, surrounded by water, is pierced from the east by the Arabian Gulf and the Red Sea, and from the west by the waters of the Mediterranean.

Later mapmakers of the tenth and eleventh centuries were often slave dealers or traders, making their way north to the shores of the Caspian Sea and up the Volga River deep into the heart of Asia. Asian tribesmen, Russians, Norsemen, and Arabs would meet on one of the medieval world’s great trading routes, exchanging goods, knowledge, and ideas.