Autumn Books

Nature 455, 867-868 (16 October 2008) | doi:10.1038/455867a; Published online 15 October 2008

Tale of a clockwork computer

Andrew Robinson1

BOOK REVIEWEDDecoding the Heavens: Solving the Mystery of the World's First Computer

by Jo Marchant

William Heinemann/Da Capo Press: 2008/2009. 330 pp/ 288 pp. £12.99/$25

Tale of a clockwork computer

It is appropriate that Arthur C. Clarke recommended this book before his death in March 2008. Decoding the Heavens tells the story of the 2,000-year-old Antikythera Mechanism and its decipherment. The tale encompasses diving, shipwrecked treasure, scientific puzzles, cutting-edge technology and computing, all of which Clarke knew from the inside. Moreover, he had a walk-on role.

The Antikythera Mechanism is an ancient Greek artefact comprising more than 30 precisely cut bronze gear wheels, dials and pointers held in a wooden case.

Clarke began to publicize the mechanism in 1959, perhaps encouraged by his friend Jacques Cousteau, who in 1953 had reinvestigated an ancient shipwreck off the Greek island of Antikythera, which had been salvaged by roving Aegean sponge divers in 1900–01. In 1965, Clarke tracked down the mechanism's encrusted remains languishing in a cigar box at the National Archaeological Museum in Athens, later televising it in Arthur C. Clarke's Mysterious World in 1980. If the ancient Greeks had been able to build on the knowledge required to make the mechanism, he told a Smithsonian Institution audience in 1973, by now humans might be exploring the nearer stars, not merely the inner Solar System.

Yet, as Clarke admits on the book's jacket, the Antikythera Mechanism remains "under-rated". The instrument was known only to a small circle of enthusiasts until a paper was published in 2006 explaining its operation, based on X-ray images of the interior and a new technique for illuminating previously hidden surface inscriptions (T. Freeth et al. Nature 444, 587–559; 2006). Jo Marchant, then a Nature staff journalist, wrote a news feature to accompany the paper, and the book grew from her research. Decoding the Heavens is Marchant's first book and is aimed squarely at the non-scientific reader, but is serious about the science. Her gripping and varied account will propel the mechanism to greater fame, although it may never achieve the celebrity of the Rosetta Stone that it probably deserves.

The complexity of the mechanism suggests that the ancient Greeks had achieved a level of clockwork technology not reached again until the Industrial Revolution of the eighteenth century. "It's hard to overestimate the uniqueness of the find. Before the Antikythera Mechanism, not one gearwheel had ever been found from antiquity, nor indeed any example of an accurate pointer or scale. Apart from the Antikythera Mechanism, they still haven't," Marchant explains.

The original 1900–01 dive was the first archaeological exploration of a wreck, undertaken decades before Cousteau's invention of the scuba apparatus. After describing its drama, Marchant turns to the scholars from many countries who tried to date and interpret the mechanism over the next century. In the 1960s and 1970s, the leading investigator was the late science historian Derek de Solla Price of Yale University, who published Gears from the Greeks (American Philosophical Society, 1974). Since the 1990s, two rival explanations have emerged: one from Michael Wright, a former curator at the Science Museum in London, who is inspired by de Solla Price, and the other from the multidisciplinary team that published in Nature, led by mathematician and film-maker Tony Freeth and Mike Edmunds, an astronomer at Cardiff University. Marchant's handling of the rivalry is excitingly tense.

Damaged Greek inscriptions initially dated the mechanism to between the second century bc and the second century ad. Radiocarbon analysis dated the ship's wooden hull to between 260 and 180 bc, although the ship could have sailed later. The design of the wreck's pottery amphorae narrowed the date to the first half of the first century bc. Silver and bronze coins found by a second Cousteau expedition in 1976 showed the ship sank between 70 and 60 bc, probably while sailing from Pergamon, on the coast of Asia Minor, towards Rome.

The mechanism was initially thought to be an astrolabe. But its gear wheels suggested another use, as astrolabes do not need gears. De Solla Price imagined it was a calendar computer, but this did not explain the ratios of teeth on the gears. Wright now favours a planetarium explanation, whereas Freeth's team believes it is an instrument for predicting eclipses. Freeth prefers to call it a 'calculator' rather than a 'computer', whereas Marchant, following historian Doron Swade's definition that a computer can display its calculated numbers on a scale, uses the latter. In both explanations, the mechanism's builders assumed that Earth is at the centre of the heavens, as believed by Greek astronomers and philosophers except for the heliocentric Aristarchus of Samos, and that the movement of the heavenly bodies is based on epicycles.

Marchant's fascinating final chapter asks who made it, and why. The inventions of Archimedes in the third century bc might have influenced it; an epigraphic analysis published earlier this year hints at a link with his home city of Syracuse (T. Freeth et al. Nature 454, 614–617; 2008). The astronomer Hipparchus may also have inspired its design, but was probably dead before its construction. The philosopher Posidonius, who lived at the right time, is a strong candidate; his student Cicero mentions that Posidonius built an instrument that reproduced the "motions of the Sun, the Moon and the five planets".

The mechanism's purpose may have been for astrology, in which Hipparchus apparently believed, but more likely it had no practical use. Like the orreries of the Enlightenment, it was probably one among many luxury gadgets for the educated Greek and Roman elite — the only example of its kind to survive. "The Antikythera Mechanism," Marchant concludes, "was originally meant as a celebration of the heavens."

  1. Andrew Robinson is a visiting fellow at Wolfson College, Cambridge. He is the author of Lost Languages: The Enigma of the World's Undeciphered Scripts and The Story of Measurement.
    Email: ar471@cam.ac.uk

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