Horology: The Antikythera Gear Wheel

Horology: The Antikythera Gear Wheel

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The discovery of a shipwreck by sponge divers off the coast of the Greek island Antikythera in 1900, lead to the recovery of a large collection of sculpture and bronze artefacts. When these were examined at the National Museum of Archeology in Athens, the items included a ‘fossil’ featuring, what seemed to be, a corroded gear wheel. The mechanism was dismissed as being, clearly, of a much later date and research was concentrated on the many other artefacts.

Although it was examined again in the 1950s, it was not until a scientific examination by Derek Price, with the help of a Greek Nuclear Physicist, that the mechanism was photographed using X-rays and Gamma rays. The images revealed much more of the complexity of the gearing and determined that the mechanism was indeed contemporary with the shipwreck.

Although it is not a clock, it is a kind of planisphaerium and is on a level of sophistication with the complex calendar dials which appeared on public clocks during the middle ages. It was cased in a wooden box roughly the size of a modern shoe box and was ‘powered’ by turning different handles on the sides of the case. Using the earliest known example of epicyclic gearing, the front dial accurately moves the corresponding positions of the 5 planets known to the Greeks whilst the dials on the rear of the mechanism are domestic calendars.

Recent scientific research, using the most powerful modern X-ray cameras available, have revealed further details of the gear counts and Ancient Greek inscriptions.

The most unexpected function is the ability to calculate lunar eclipses over a four-year cycle. This, including Northern and Southern positions, was possibly used to confirm the Rhodian calendar which was integral to their rituals and administration.

Other recently discovered dials on the back include the four-year cycle of the PanHellenic and Olympic games whilst another dial is shown to be the Metonic cycle which is engraved with the Corinthian months.

An illuminating way of seeing the mechanism is provided by some of the models and reconstructions which are lent to museums. The former curator of the Science Museum in South Kensington, Michael Wright has researched and overseen much of the investigation and has produced his own model which can be seen on BBC iplayer, The 2000 Year Old Computer.

The pedigree of the piece is lost in the mists of time but it has now been determined, comprehensively, to have been built circa 81 BC. It was made, then, less than 150 years after the death of Archimedes in Syracuse. No other known mechanism exists and given the details it offers,it inspires a new outlook on the cultures and  abilities of the Ancient Greeks.

Jonathan McNabb

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