Thursday, July 31, 2008

Ancient Greek 'computer' an astronomical tool

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INSCRIPTIONS on a mysterious 2000-year-old clockwork device suggest that the artefact was inspired by earlier devices made by the great Greek mathematician Archimedes.

The so-called "Antikythera mechanism" has puzzled historians since it was salvaged from an ancient shipwreck near the Greek island of Antikythera in 1901. It dates back to about 100 BC, and consists of more than 30 bronze gear wheels and pointers, enclosed in a wooden case.

The device is by far the most advanced scientific instrument to survive from antiquity - nothing else close to its complexity shows up in archaeological records for more than 1200 years, when mechanical clocks appeared in medieval Europe.

The Antikythera mechanism is thought to be a mechanical computer, which used sophisticated algorithms to calculate the motions of celestial bodies. A dial on the front showed the position of the sun, moon and probably the planets in the zodiac, while the back displayed a 19-year lunisolar calendar, as well as the timing of eclipses (Nature, DOI: 10.1038/nature05357; Interdisciplinary Science Reviews, vol 32, p 27).

The mechanism may have been used by philosophers to show the workings of the heavens, as suggested by the Roman author Cicero, who wrote in the 1st century BC of bronze devices that erroneously modelled the movements of the sun, moon and planets around Earth.

The origin of the Antikythera mechanism was a mystery, but newly deciphered inscriptions show that its calendar used local month names. They match those used by Greek colonies founded by the city of Corinth, and a prime candidate is Syracuse, in Sicily (Nature, DOI: 10.1038/nature07130).

Alexander Jones of the Institute for the Study of the Ancient World in New York, who deciphered the inscriptions, says the presence of a local calendar supports the idea that rather than being used by astronomers, the mechanism was intended for demonstrations, albeit to a small, educated elite.

Jones and his colleagues say the identification of Syracuse is intriguing because one of the models Cicero mentioned in his writings was made by Archimedes in the 3rd century BC. Archimedes worked in Syracuse, so the Antikythera mechanism, made at least a century later, might be part of a tradition of geared mechanisms begun by the legendary mathematician.

But this also prompts a new mystery, because the wreck on which the mechanism was found was a Roman ship, sailing not from Sicily but from the eastern Mediterranean in 70-60 BC, mostly likely taking looted Greek treasures back to Rome.

"The route of the ship is puzzling," says Paul Cartledge, a professor of Greek history at the University of Cambridge, UK. "It was going from east to west, and Antikythera is well to the east of Syracuse."

Cartledge says it's not impossible that the instrument was designed in the east – Rhodes or Alexandria say – for use in Syracuse.

However the mechanism seems to have been several decades old when it was taken on its final journey. So perhaps it was made in Syracuse for a wealthy owner who subsequently moved to the eastern Mediterranean, or was carried there as a gift or votive offering, before later becoming part of booty taken for Rome.



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