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ANAXIMANDER’S VISION

In 1963, I was introduced to a new world and my vision of our planet took a major leap forward when I embarked on a trip to Greece. While in this historic landscape, with its ruins dating back across the ages, I began to dwell upon the world of the Ancient Greeks. Their concept of the world depended on understanding the natural world that was most familiar to them, one not so different from that known to the Babylonians, except it was a little further west and included a greater familiarity with the Mediterranean Sea and the lands around it.

In the 6th century BCE, in the thriving Ionian Greek city of Miletus, arose a school of pragmatic thinkers who, to some extent, freed themselves from the confines of belief in the Olympian gods; in the words of T. B. Parrington, a British classicist, ‘Technology drove mythology from the field.’ Reason ruled the day, at least in the cosmopolitan city of Miletus. A citizen of this city, Thales (624–546 BCE), possessed a great intellectual talent and, after making a considerable fortune in the olive oil business, retired and spent his time in the study of the cosmos, the Greek word for universe, meaning ‘order’. He studied the movements of the sun, moon and celestial bodies, and also the work of Babylonian and Egyptian researchers. Thales gained notoriety by predicting the solar eclipse of 585 BCE. His view was that by ignoring the mysticism of mythology and observing the natural order, it must be possible to discover the fundamental order of things. He concluded that all things must originate as water and developed the idea of a flat, disc-shaped earth floating on water, the primary substance – not unlike the Babylonian vision of 1,500 years earlier.

Map 4. The geographer Eratosthenes claimed that Anaximander published the first map of the world. Anaximander was undoubtedly influenced by earlier maps, including the Babylonian world map.

Map 5. Hecataeus is credited with improving upon the work of Anaximander. He created a more detailed interpretation of the world, approximately 80 years after Anaximander.

A fellow citizen, Anaximander (610–546 BCE), is assumed to have been a pupil of Thales, who was 14 years his senior. Thales – in whose mind observations of earlier societies and Greek philosophy had coalesced – certainly influenced Anaximander. In the theories attributed to him, the diversion from traditional myths and rational thought became obvious – he believed the world floated in the ‘infinite’ but was a cylinder in shape. Its inhabitable surface, on top of the cylinder, was surrounded by a circular ocean, reminiscent of the Babylonian concept. According to the geographer Eratosthenes, Anaximander was the first to publish a map of the known world, centred on, or at least near, his home city of Miletus. Hecataeus (550–476 BCE), also of Miletus, was inspired by Anaximander’s map to create his own version with added detail and produced a prose world history that separated out tradition and myth, relying on factual evidence wherever possible.

ERATOSTHENES AND THE WELL AT SYENE

Alexandria, founded on the northern coast of the Nile delta by Alexander the Great in 332 BCE, prospered after its foundation, far outliving the empire of Alexander, which fell apart after his death. Alexandria came under the rule of the Ptolemies, perhaps the most successful inheritors of his domains. They ruled with a relatively heavy hand, exacting high taxes to pay for a powerful army and navy, but they realised that knowledge was power and they had cultural ambitions. The manifestation of that power was the Great Library at Alexandria. The Ptolemies invested heavily in this fine institution; they even developed a policy that any ship arriving in Alexandria’s thriving port, guided into safe anchorage by the great ‘Pharos’ lighthouse, could be searched for scrolls and learned documents, which would be confiscated from their owners. These would then be carefully copied and the copies would be handed back to their owners, while the originals were placed in the library. Under the patronage of the Ptolemies, Alexandria attracted mathematicians, philosophers and scientists of all kinds. The lights of the Pharos guided valuable trade into Alexandria, but the reach of Alexandria’s influence ran well beyond the shores of the Mediterranean Sea – perhaps what modern politicians and diplomats now describe as ‘soft power’.

Eratosthenes (275–194 BCE), born in Cyrene and educated in other places including Athens, was a polymath and intellectual philosopher, geographer and mathematician who is reputed to have written a history of comedy, a chronology of major events in the Hellenistic world and also poetry. It was this gifted thinker that Ptolemy III, Euergetes, appointed head of Alexandria’s famous library in around 245 BCE. Eratosthenes, at the age of 31, now found himself the librarian in charge of the greatest concentration of knowledge in the known world and was able to sift through new scrolls and reports arriving in the Great Library. This position made Eratosthenes among the most respected scholars in the Greek world.

Map 6. Eratosthenes produced a new world map based on his mathematical studies for measuring the earth’s circumference. He also divided the world into climatic regions.

Among the scrolls was a report of the well of Syene on the Nile River. The report stated that at high noon the sun shone directly down this deep well, lighting its dark waters on the longest day of the year, 21 June. Eratosthenes assumed, based on observations by earlier and contemporary astronomers, that this must mark the northern edge of the tropics. The astronomers of the age believed that the sun, moon and stars rotated around a static earth; from this perspective, they also began to perceive that the sun moved around the earth each day and that, through its annual 365-day cycle, it was higher in the sky in summer than in other seasons of the year. This they called its ‘ecliptic’.

Aristarchus of Samos (310–230 BCE) had proposed a theory^* that the sun was the centre of the known universe and that the earth revolved around it. He had even suspected that the stars were other suns but much further away. However, it is known that Eratosthenes rejected this idea, as Ptolemy did centuries later.

When the ecliptic was plotted, astronomers also noted that the sun was almost always at an angle to the equator, the imaginary line that divided the celestial sphere of the earth. The sun’s migrations were calculated to go from 24 degrees south to 24 degrees north of the equator, before returning on the same course; this was called the ‘obliquity of the ecliptic’. Now hang in there for a moment …

Though the Greeks spoke of land below the tropics, the consensus of opinion was that people could not live ‘down’ there. However, the development of the idea of the earth as a sphere divided by the equator into hemispheres, with lines of latitude marked by the tropics of Cancer and Capricorn, gave geographers their first three reference lines for the making of maps. The northern tropic was named Cancer, which is when the constellation of the Crab (Cancer) appears in the night sky. Likewise, the southern tropic was named Capricorn after the first appearance of the constellation of Capricorn, the horned goat.

Eratosthenes’ understanding of the cosmos meant that he could now set about measuring the earth. For his calculations, he considered that the sun’s rays would be parallel when they reach earth. Therefore, as the earth was a sphere, the sun’s light must hit different parts at different angles. Now he knew that the sun shone straight down the well at Syene and the town’s buildings cast no shadow when the sun was almost directly above. At the same moment in Alexandria, the buildings cast a shadow. Therefore, he concluded that if he could measure the angle of the shadow on that particular day at high noon, he might just be able to work out the size of the earth.

Eratosthenes understood that Syene was some 5,000 stades (800 kilometres) due south of Alexandria, and thus on the same meridian (a meridian is half of a circle, from pole to pole that crosses the equator at a right angle). If he could determine the distance between the two locations, this would give him the exact length of the arc of the meridian, the part between the two points, and therefore part of the circumference of the earth. This left him with one unknown in his calculation: if the arc between Syene and Alexandria represented 5,000 stades, what fraction of the full circle of the earth did that represent? Eratosthenes used a gnomon to work this out (a vertical pole used to measure time, set in a public place for everyone to use). When the gnomon’s shadow hit the meridian line, the sun was at its zenith. Eratosthenes carefully measured the shadow and the height of the gnomon, which gave him two sides of a triangle. He then drew the third side, and now he could work out the angle of the sun’s rays from the top of the gnomon to the edge of the shadow. This turned out to be 7 degrees 12 minutes, almost one-fiftieth of a complete circle, therefore 50 x 5,000 meant the earth was 250,000 stades in circumference, or about 46,000 kilometres. We now know, of course, that the earth is just over 40,000 kilometres around the equator.

Eratosthenes had come pretty close to the correct answer, based on the tools and geographic knowledge available to him. There were mistakes: the earth is not a perfect sphere; Syene is not exactly on the tropic of Cancer (it is 60 kilometres north) and is not on the same meridian (it is 3 degrees 3 minutes east). However, Eratosthenes had established some of the elementary rules in cartography and, for many mapmakers that would follow, the importance of astronomy in calculating your bearings on earth.

During his lifetime, Eratosthenes’ researches covered many fields – his colleagues nicknamed him ‘Beta’ because he covered so much that he always came second (Beta is the second letter of the Greek alphabet). Perhaps there was a hint of jealousy on their part. Other admirers called him Pentathlos after the Olympian athletes who were all-rounders and capable competitors.

In old age, Eratosthenes contracted ophthalmia and became blind, leaving him no longer able to read the scrolls in the Great Library or to observe nature and the heavens. Frustrated, he chose to starve himself to death, dying in 194 BCE aged 82, probably in his beloved library.

* The Greek Heliocentric Theory.