The Antikythera device was found by chance in the remains of an ancient ship, discovered sometime before Easter 1900 at a depth of 42 m. Many statues and other artifacts were retrieved on site by Greek sponge divers. The mechanism itself was discovered on May 17, 1902, when archaeologist Valerios Stais noticed that a piece of rock recovered from the site had a gear wheel embedded in it.

Upon examination, it was found that the “rock” was in fact a heavily encrusted and corroded mechanism which had survived in three main parts and dozens of smaller fragments. The device itself was surprisingly thin; about 33cm (13in) high, 17cm (6.75in) wide and 9cm (3.5in) thick, made of bronze and originally mounted in a wooden frame. It was inscribed with a text of over 2,000 characters, of which about 95% have been deciphered. The full text of the inscription has not yet been published. The device is displayed in the Bronze Collection of the National Archaeological Museum of Athens, accompanied by a reconstruction. Another reconstruction is on display at the American Computer Museum in Bozeman, Montana

Origins
The origins of the mechanism are unclear, as are the circumstances in which it came to be on the Antikythera ship. The ship was a Roman one, though there is no doubt that the mechanism itself was made in Greece. One hypothesis is that the device was constructed at an academy founded by the ancient Stoic philosopher Posidonios on the Greek island of Rhodes, which at the time was known as a centre of astronomy and mechanical engineering. Investigators have suggested that the ship could have been carrying it to Rome, together with other treasure looted from the island to support a triumphal parade being staged by Julius Caesar.

Function and purpose
Schematic of the artifact’s mechanismThe Antikythera mechanism is one of the world’s oldest known geared devices. It has puzzled and intrigued historians of science and technology since its discovery. Following decades of work in order to clean the device, systematic investigations were undertaken in 1951 by British historian of science Derek J. de Solla Price. In June 1959, in a front-page article in Scientific American titled “An ancient Greek computer”, he brought forth the theory that the Antikythera mechanism was a device for calculating the motions of stars and planets, which would make the device the first known analog computer. Up until that time the function of the Antikythera mechanism was largely unknown, though it had been correctly identified as an astronomical device, perhaps being an astrolabe. In 1971 Price, by then having been appointed as the first Avalon professor of history of science at Yale University, teamed up with Charalampos Karakalos, professor of nuclear physics at the Greek nuclear research centre “DEMOKRITOS”. Karakalos had gamma- and X-ray analysis carried out on the mechanism on behalf of Price, in this way revealing critical information concerning the device’s interior configuration. In 1974 Price authored “Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 B.C.”, where he presented a model of how the mechanism could have functioned. Recent research breakthroughs confirm Price’s theory (see below).

The device uses a differential gear — previously believed to have been invented in the 16th century — and is known for the level of miniaturization and complexity of its parts, which is comparable to that of clocks made in the 18th century. The differential gear arrangement is composed of 30+ gears with teeth formed through equilateral triangles. When past or future dates were entered via a crank (now lost), the mechanism calculated the position of the Sun, Moon or other astronomical information such as the location of other planets. The use of differential gears enabled the mechanism to add or subtract angular velocities. The differential was used to compute the synodic lunar cycle by subtracting the effects of the sun’s movement from those of the sidereal lunar movement. It is possible that the mechanism is based on heliocentric principles, rather than the then-dominant geocentric view espoused by Aristotle and others. This may indicate that the heliocentric view was more widely accepted at the time than was previously thought.

It is possible that the Antikythera mechanism was not unique. Cicero, writing in the 1st century BC, mentions an instrument “recently constructed by our friend Posidonius, which at each revolution reproduces the same motions of the sun, the moon and the five planets.” (Cicero was himself a student of Posidonius.) Similar devices are mentioned in other ancient sources. It also adds support to the idea that there was an ancient Greek tradition of complex mechanical technology which was later transmitted to the Arab world, where similar but simpler devices were built during the medieval period. The early 9th century Kitab al-Hiyal (“Book of Ingenious Devices”), commissioned by the Caliph of Baghdad, records over a hundred mechanical devices described in Greek texts that had been preserved in monasteries. Such knowledge could have yielded to or been integrated with European clockmaking and ancient cranes.

The device’s full range of capabilities is unknown. Some investigators believe that the Antikythera mechanism could have been used to track celestial bodies for auspicious occasions such as religious events or births. Price suggested that it might have been on public display, possibly in a museum or public hall in Rhodes.
The island was known for its displays of mechanical engineering, particularly automata, which apparently were a specialty of the Rhodians; to quote Pindar’s seventh Olympic Ode:

The animated figures stand
Adorning every public street
And seem to breathe in stone,
or move their marble feet.

Investigations and reconstructions

Price
Reconstruction of the Antikythera mechanism in the National Archaeological Museum, Athens (based on Wright’s model) Price’s model, as presented in his “Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 BC”, was the first, theoretical, attempt at reconstructing the device. According to that model, the front dial shows the annual progress of the Sun and Moon through the zodiac against the Egyptian calendar. The upper rear dial displays a four-year period and has associated dials showing the Metonic cycle of 235 synodic months, which approximately equals 19 solar years. The lower rear dial plots the cycle of a single synodic month, with a secondary dial showing the lunar year of 12 synodic months. A British orrery maker named John Gleave constructed a replica based hereupon, though with some very slight modifications of his own in order for it to be functional. The following link gives an idea of the internals of this device, though later researchers have doubts as to whether Price’s model is an accurate representation of the original Antikythera mechanism

Bromley & Percival
An ingenious variant on Price’s reconstruction was built by Australian computer scientist Allan George Bromley (1947–2002) of the University of Sydney and Sydney clockmaker Frank Percival. Bromley went on to make new, more accurate X-ray images in collaboration with Michael Wright (see below). Some of these were studied by Bromley’s student, Bernard Gardner, in 1993

Wright
2005 X-ray image of the Antikythera mechanismAll previous reconstructions rely on data taken from the description by Derek J. de Solla Price. Michael Wright, formerly Curator of Mechanical Engineering at The Science Museum, London, and now of Imperial College, London, made a completely new study of the original fragments together with Allan Bromley. For this, Wright designed and made apparatus for linear tomography, allowing resolution of radiographic images in three dimensions.

The new data from this survey supersedes that of Price. Working from it, Wright has, between 2002 and 2005, developed an entirely different reconstruction. The arrangement of the surviving gearing is not as Price described. The function of both back dials is changed. There is evidence that further mechanism has been lost from under the front dial and that this dial display was more elaborate than previously supposed. Wright’s working model demonstrates the possibility that it might have been a fully-elaborated planetarium, corresponding to those mentioned in ancient literature. (Follow external link.)

Wright points out that the detail of the instrument is less important than its significance as artifactual evidence for an established tradition of geared mechanism in Hellenistic antiquity that is otherwise known only through literary references. A line of development may be traced from these devices, through similar ones described in Arabic sources, to the medieval rise of the mechanical tradition of Western Europe.

Antikythera Mechanism Research Project
The Antikythera mechanism is now being studied by the Antikythera Mechanism Research Project, a joint program between Cardiff University, the National and Kapodistrian University of Athens, the Aristotle University of Thessaloniki, the National Archaeological Museum of Athens, X-Tek Systems UK and Hewlett-Packard USA, funded by the Leverhulme Trust and supported by the Cultural Foundation of the National Bank of Greece.

The mechanism’s fragility precluded its removal from the museum, so the Hewlett-Packard research team and X-Tek systems had to bring their devices to Greece. HP built a 3-D surface imaging device, known as the “PTM Dome”, that surrounds the object under examination. X-Tek systems developed especially for the Antikythera Mechanism a 12 ton 450kV microfocus computerised tomographer. It was announced in Athens on 21 October 2005 that many new pieces of the Antikythera mechanism had been found. There are now more than 70 fragments. Most of the new pieces had been stabilized but were awaiting conservation. On 30 May 2006 it was announced [2] that the imaging system had enabled much more of the Greek inscription to be viewed and translated, from about 1,000 characters that were visible previously, to about 2,000 characters, representing about 95% of the non-lost text. The team’s findings might shed new light concerning the function and purpose of the Antikythera mechanism. Research is ongoing.

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