Ancient Greek Computer Reconstructed

afaik_ianal writes "A working reconstruction of an ancient Greek computer, the Antikythera mechanism, which was found at the bottom of the ocean in 1900 has been unveiled and is on display at the Technopolis museum, in Athens. The device is believed to have been used to calculate the positions of various celestial bodies including the sun and the moon on any given date. While some guesswork was required in the reconstruction, the bulk of the design is based on updated X-ray photographs of the device."

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[loraksus]

(notice the date, not quite "news")

The Antikythera mechanism
The clockwork computer

Sep 19th 2002
From The Economist print edition
An ancient piece of clockwork shows the deep roots of modern technology

WHEN a Greek sponge diver called Elias Stadiatos discovered the wreck of a cargo ship off the tiny island of Antikythera in 1900, it was the statues lying on the seabed that made the greatest impression on him. He returned to the surface, removed his helmet, and gabbled that he had found a heap of dead, naked women. The ship's cargo of luxury goods also included jewellery, pottery, fine furniture, wine and bronzes dating back to the first century BC. But the most important finds proved to be a few green, corroded lumps--the last remnants of an elaborate mechanical device.

The Antikythera mechanism, as it is now known, was originally housed in a wooden box about the size of a shoebox, with dials on the outside and a complex assembly of bronze gear wheels within. X-ray photographs of the fragments, in which around 30 separate gears can be distinguished, led the late Derek Price, a science historian at Yale University, to conclude that the device was an astronomical computer capable of predicting the positions of the sun and moon in the zodiac on any given date. A new analysis, though, suggests that the device was cleverer than Price thought, and reinforces the evidence for his theory of an ancient Greek tradition of complex mechanical technology.

Michael Wright, the curator of mechanical engineering at the Science Museum in London, has based his new analysis on detailed X-rays of the mechanism using a technique called linear tomography. This involves moving an X-ray source, the film and the object being investigated relative to one another, so that only features in a particular plane come into focus. Analysis of the resulting images, carried out in conjunction with Allan Bromley, a computer scientist at Sydney University, found the exact position of each gear, and suggested that Price was wrong in several respects.

In some cases, says Mr Wright, Price seems to have "massaged" the number of teeth on particular gears (most of which are, admittedly, incomplete) in order to arrive at significant astronomical ratios. Price's account also, he says, displays internal contradictions, selective use of evidence and unwarranted speculation. In particular, it postulates an elaborate reversal mechanism to get some gears to turn in the right direction.

Since so little of the mechanism survives, some guesswork is unavoidable. But Mr Wright noticed a fixed boss at the centre of the mechanism's main wheel. To his instrument-maker's eye, this was suggestive of a fixed central gear around which other moving gears could rotate. This does away with the need for Price's reversal mechanism and leads to the idea that the device was specifically designed to model a particular form of "epicyclic" motion.

The Greeks believed in an earth-centric universe and accounted for celestial bodies' motions using elaborate models based on epicycles, in which each body describes a circle (the epicycle) around a point that itself moves in a circle around the earth. Mr Wright found evidence that the Antikythera mechanism would have been able to reproduce the motions of the sun and moon accurately, using an epicyclic model devised by Hipparchus, and of the planets Mercury and Venus, using an epicyclic model derived by Apollonius of Perga. (These models, which predate the mechanism, were subsequently incorporated into the work of Claudius Ptolemy in the second century AD.)

A device that just modelled the motions of the sun, moon, Mercury and Venus does not make much sense. But if an upper layer of mechanism had been built, and lost, these extra gears could have modelled the motions of the three other planets known at the time--Mars, Jupiter and Saturn. In other words, the device may have been able to predict the positions of the known celestial bodies for any given date with a respectable degre

Re:Is it a computer?

[iocat]

It's a single-problem solving analog computer of the classic, pre-Turing sense. They used to have all kinds of crap like this for solving various problems. Easier (at the time) (and probably cooler) than a book filled with lists. Not a Turing complete machine by any sense... more like the ABC device that people are always claiming was the "first computer," than an ENIAC.