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Rev · 30th November 2006, 07:57

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Ancient Greek computer reveals its secrets

By Roger Highfield, Science Editor
Last Updated: 2:00am GMT 30/11/2006

Video: 3D animation of the mechanical computer
Video: The computer's inner workings

A bronze calculating machine salvaged from a shipwreck a century ago is finally yielding up its secrets, revealing a Greek computer of remarkable sophistication for a device constructed long before the birth of Christ.

Scholars have been baffled by the 80-plus fragments of the ancient mechanism found in 1901 by sponge divers in a Roman shipwreck near the island of Antikythera, midway between the Peloponnese and Crete.
Around the size of a discus, the device was so badly corroded that it had the consistency of flaky pastry and was encrusted with deposits. Yet it seemed to be the earliest-known machine involving an arrangement of gear-wheels, built centuries before such technology became commonplace.
Was it a rich man's toy? Or was it an orrery or an astronomical clock? Or something else that reflected an ancient interest in astrology?
In the wake of a study of its workings published today in the journal Nature, the "Antikythera Mechanism" will transform the way we think about the technological capabilities of the ancient world.
An international team unveils a new reconstruction of the way its gears worked and has doubled the number of deciphered inscriptions on the casing. It reveals a spectacular and ancient astronomical calculator that may even have been designed by Hipparchos (190BC-120BC) himself, arguably the greatest astronomical observer of antiquity, or by his followers.
Prof Mike Edmunds and Dr Tony Freeth of Cardiff University and colleagues in Greece and America say it was used to chart the movement of the Moon and Sun, along with eclipses and perhaps even the passage of Mercury and Venus.
The hand-driven mechanism was not a true computer, since its "program" could not be changed. Nonetheless, it would have been a wonder of its age, the supercomputer of its day, which could do multiplication, division, addition and subtraction.
Although the wreck has been dated to 65 BC, the device itself was probably built around the end of the second century BC. One of the provocative issues raised by this machine, said Prof Edmunds, is what other mechanical devices the ancient Greeks managed to construct.
"It does raise the question what else were they making at the time," he said.
Another profound question is how this extraordinary technology was lost when the Roman Empire came to dominate the Mediterranean. "In terms of historic and scarcity value, I have to regard this mechanism as being more valuable than the Mona Lisa," he added.
The new study vindicates pioneering work carried out from the late 1950s to the early 1970s by late British historian of science, Prof Derek De Solla Price. After studying the mechanism with X rays, he wrote in his book Gears from the Greeks that it had been used as an astronomical calendar.
But because his analysis demanded a complete rethink of the capabilities of ancient Greek technology, it came under attack from academics who put alternative ideas forward.
Today, although details of his work are clearly wrong, Price's overall thesis is vindicated. The new glimpse of this ancient celestial apparatus dates back to last year, when the Antikythera Mechanism Research Project - an international collaboration - was given access to the remains the National Archaeological Museum in Athens and used modern techniques to pry into its workings.
Dr Yanis Bitsakis of the National Bank of Greece Cultural Foundation, Prof Edmunds and colleagues used imaging techniques that could shed new light on apparently impossible to decipher inscriptions, not helped by how the Greeks left no gaps between words.
Analysis of the now much clearer lettering indicates a construction date of between 150 BC and 100 BC, slightly earlier than had been assumed, describes how it was made and used, and information on various motions of the heavens. Because it is so fragile, a 7.5 ton X-ray tomography scanner - akin to the kind used on patients - had to be taken to the museum to study the device.
This revealed a complicated arrangement of 30 precision, hand-cut bronze gears, housed inside a wooden case covered in inscriptions.
From their studies, they have inferred that there were at least seven more gears, along with iron or steel axles, marking a major departure from the pioneering work of Prof Price.
Overall, the mechanism is technically more complex than any comparable known mechanical device for at least a millennium afterwards. "It is as complicated as a clock," said Prof Edmunds. "It is only when you get Medieval astronomical clocks that you go beyond this in complexity."
Francois Charette of Ludwig-Maximilians-University, said that scholars are "stunned at the ingenuity of the ancients" but there will be plenty more speculation about how this marvel was used.
To help answer these questions, the team is now building a virtual version in a computer. The Antikythera Mechanism also reveals that the history of technology is far from linear, since the ancient Greeks achieved a level of instrument-making not surpassed until the Renaissance.
Prof Edmunds said: "It makes you wonder what they would have achieved if they'd have carried on, and the Romans hadn't taken over and put a stop to things. Would they have had a man on the Moon by AD 300?
"It sounds ridiculous, but if they were able to construct something as technically brilliant as this, it's not complete fantasy," said Prof Edmunds.
"The Romans were great at the stuff like building sewers and getting things done, but it was the Greeks who were the thinkers, and came up with real innovative technology."

http://www.telegraph.co.uk/news/main.../ugreek129.xml