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June 08, 2006

The Antikythera mechanism

Michael Wright, curator of mechanical engineering at the Science Museum in London, has deployed linear tomography to produce the best ever imagery of the remaining inner workings of the Antikythera mechanism. Recovered by a sponge diver in 1900 in the wreck of an ancient cargo ship, the device has long been thought to have been an astronomical computer. Wright's analysis appears to prove the case.

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.)

Posted by Ghost of a flea at June 8, 2006 09:33 AM