Antikythera Mechanism

10 Sep 2021

William also sent in this link. On the Antikythera Mechanism - see Current World Archaeology 108 [August/September 2021] pages 16-23 [see also ] and T Freeth et al [2021] 'A Model of the Cosmos in the Ancient Greek Antikythera Mechanism' in Scientific Reports at ... It has been described as a computer. A mechanism to calculate, or compute. It is a testament to Greek ingenuity - but what was it used for?

The device was found in a shipwreck between Crete and mainland Greece, near the island of Kythera, back in 1901. It was amongst a treasure of bronze sculptures, glassware, jewelry, amphorae, and tableware etc. The mechanism, at that time, was just a big lump - the size of a large dictionary. A month after it was recovered the object split apart, revealing tiny gear wheels, the size of coins. No one thought such precision gearing could exist in the ancient world - but these gear wheels did. Just a third of the original survives, in a Greek museum. It consists of 82 fragments - just a third of the original. It is a jigsaw puzzle that has perplexed succeeding generations. Over the years various people have tried to work out what it was meant to do. Now, a team from UCL in London has come up with a model that is riding on the back of earlier researchers. They also used the research notes of Albert Rehm, from back in the early 20th century, which was unpublished. He red inscriptions on the mechanism concerning the risings and settings of the planets as viewed from the earth - and discovered astronomical cycles too [the 19 year and 76 year cycles of the moon for example, as well as an eclipse cycle]. The planets Mercury, Mars, Venus, Jupiter, and Saturn, were displayed in a ring system at the front of the mechanism, he claimed. More than a century later Rehm's ideas lie at the core of the new model. In between, in mid 20th century,  Derek de Solla Price, began a 20 year bout of research on the mechanism, using x-rays on the fragments. He was able to identify that there were 30 surviving gears. Later, Michael Wright took up the research, broadening Price's suggestion about the planets.

The Greeks thought the planets orbited around the earth, rather than around the sun. When viewed from earth Venus is sometimes ahead of the sun and sometimes behind the sun. Similar motions apply to all the planets - which created a problem for ancient astronomers. The Babylonians had discovered that Venus goes through five synodic cycles every 8 years - hence were able to predict the future positions of Venus, and in a similar fashion, those of the other planets. The Greeks built on this by proposing geometrical theories for explaining the planetary motions. These theories were ideal for mechanising the motions of the planets in a general mechanism. Astronomical changes could be calculated by turning a handle.

Wright had found evidence of bearing and other structures on the Main Drive Wheel. This four spoked gear is prominent at the front of Fragment A. It is fronted by the impact handle and rotates once a year - setting all the other gears in motion etc. He published his ideas in 2002, which were received favourably at first. However, later there were multiple challenges to his work - hence the germ of the decision for the UCL study. They used Microfocus X-ray Computed Tomography and Polynomial Texture Mapping [a digital imaging technique]. All 82 fragments were scanned. Two discoveries were made. A dial on the back predicted eclipses - which Rehm has recognised, involving a 223 tooth gear [for a 233 month cycle]. They also found the driver could model the movement of the moon - which also involved the 223 toothed gear. Tw inscriptions were found - one of the back and one at the front. They described a model of the Cosmos with the sun show as a pointer, a ring system for the planets, and marker beads to indicate each planet etc. A fascinating piece of research - by all of them, from Rehm to the UCL team.