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Thursday, November 30, 2006

Vintage Compuer: An Ancient Computer Surprises Scientists

The New York Times
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November 29, 2006

An Ancient Computer Surprises Scientists

A computer in antiquity would seem to be an anachronism, like Athena ordering takeout on her cellphone.

But a century ago, pieces of a strange mechanism with bronze gears and dials were recovered from an ancient shipwreck off the coast of Greece. Historians of science concluded that this was an instrument that calculated and illustrated astronomical information, particularly phases of the Moon and planetary motions, in the second century B.C.

The Antikythera Mechanism, sometimes called the world’s first computer, has now been examined with the latest in high-resolution imaging systems and three-dimensional X-ray tomography. A team of British, Greek and American researchers was able to decipher many inscriptions and reconstruct the gear functions, revealing, they said, “an unexpected degree of technical sophistication for the period.”

The researchers, led by Tony Freeth and Mike G. Edmunds, both of the University of Cardiff, Wales, are reporting the results of their study in Thursday’s issue of the journal Nature.

They said their findings showed that the inscriptions related to lunar-solar motions and the gears were a mechanical representation of the irregularities of the Moon’s orbital course across the sky, as theorized by the astronomer Hipparchos. They established the date of the mechanism at 150-100 B.C.

The Roman ship carrying the artifacts sank off the island of Antikythera around 65 B.C. Some evidence suggests that the ship had sailed from Rhodes. The researchers speculated that Hipparchos, who lived on Rhodes, might have had a hand in designing the device.

In another article in the journal, a scholar not involved in the research, François Charette of the University of Munich museum, in Germany, said the new interpretation of the Antikythera Mechanism “is highly seductive and convincing in all of its details.” It is not the last word, he concluded, “but it does provide a new standard, and a wealth of fresh data, for future research.”

Historians of technology think the instrument is technically more complex than any known device for at least a millennium afterward.

The mechanism, presumably used in preparing calendars for seasons of planting and harvesting and fixing religious festivals, had at least 30, possibly 37, hand-cut bronze gear-wheels, the researchers reported. An ingenious pin-and-slot device connecting two gear-wheels induced variations in the representation of lunar motions according to the Hipparchos model of the Moon’s elliptical orbit around Earth.

The functions of the mechanism were determined by the numbers of teeth in the gears. The 53-tooth count of certain gears, the researchers said, was “powerful confirmation of our proposed model of Hipparchos’ lunar theory.”

The detailed imaging revealed more than twice as many inscriptions as had been recognized from earlier examinations. Some of these appeared to relate to planetary as well as lunar motions. Perhaps, the researchers said, the mechanism also had gearings to predict the positions of known planets.

Dr. Charette noted that more than 1,000 years elapsed before instruments of such complexity are known to have re-emerged. A few artifacts and some Arabic texts suggest that simpler geared calendrical devices had existed, particularly in Baghdad around A.D. 900.

It seems clear, Dr. Charette said, that “much of the mind-boggling technological sophistication available in some parts of the Hellenistic and Greco-Roman world was simply not transmitted further,” adding, “The gear-wheel, in this case, had to be reinvented.”

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A Reconstruction of the
Antikythera Mechanism

Dated to ca 80 BC

In the year 1900 the bronze remains of a mechanical device were retrieved from a shipwreck off Antikythera, near Crete.

It was not clear initially what the device was, except that it was clearly a sophisticated mechanism. X-ray analysis was subsequently used to probe the inner structure of the device, the details of the gears. Finally in 1974, a full analysis was published by Professor D. De Solla Price. While some of the original gearing was missing, there was enough to work out that the device was intended to show the motion of the Moon, Sun, and most likely the Planets through the years, when the handle was turned. A few years ago, John Gleave, an orrery maker based in the United Kingdom, decided to construct a working replica of the original mechanism.

Antikythera mechanism - front

A full scale reconstruction of the Antikythera mechanism
Height 12.25 inches
The front dial - showing the annual progress of the sun & moon through the zodiac, against the Egyptian calendar, rendered in Greek on the outer annulus

Antikythera mechanism - the back dials

The back dials

The upper back dial displays a four year period and has five concentric inscribed rings, most probably each with 47 divisions giving the Metonic Cycle of 235 synodic months, which equals 19 solar years. The lower back dial gives the cycle of a single synodic month, and the subsidiary dial the Lunar year of 12 synodic months.

The original gearing was cut from bronze, and the 60 degree triangular teeth were finished using a file. In the reconstruction, the gearing is made from brass, set between perspex plates, with perspex dials in place of the original bronze, so that the mechanism is visible.

The instrument indicates that the technology of the time, of which this is the only surviving example, was by any measure sophisticated.


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