Shortly before Easter 1900, a Greek sponge diver off the small Aegean island of Antikythera discovered the wreck of an ancient ship filled with artefacts, including bronze and marble statues, dating from 85 to 50 BCE. Among the numerous finds, a small formless lump of corroded bronze and rotted wood lay unregarded at the National Museum in Athens for years. As the wood fragments dried and shrank, the lump split open to reveal the outlines of a series of gear wheels resembling clockwork. Gamma-ray photography allowed the historian of science Derek de Solla Price (1922-1983) to reconstruct the machine’s original appearance.
The gear wheels were proportioned to show the movements of the sun, moon and planets. The gears could be moved backwards and forwards, making the device a calculator that could show the positions of planets in the sky at any required date. It is nothing less than an orrery, a device well known in the Middle Ages. Further research carried out between 2006 and 2010 has enhanced our understanding of the Antikythera mechanism, revealing its high level of accuracy and enabling most of the text inscribed on its surface to be read.
Although the device is a remarkable achievement, its status should not be exaggerated. We know that the principles of gearing were understood in the Classical world and what is surprising about the Antikythera mechanism is its uniqueness: no similar gearing mechanisms have survived from antiquity. Nevertheless, we know from the Roman statesmen Cicero (106-43 BCE) that his older contemporary, the astronomer Posidonius (c 135 BCE–c 51 BCE), built such a device.
The mechanism is unlikely to have been built for purely scientific purposes, but is more likely to have been part of an astrologer’s toolkit as well as being based around the four-year Olympic cycle. It does not show a Copernican solar system, with the planets revolving around sun, but a Ptolemaic system, with the sun and planets revolving around the earth in complex motions and it has been suggested that it is rooted in Babylonian astrological belief rather than Greek. Calling it a ‘computer’ rather than an ‘orrery’ only serves to make it sound mysterious and out-of-place!