Crusty old computer: new imaging techniques reveal construction of ancient marvel.

Scientists say that they have figured out the arrangement and functions of nearly all the parts of a mysterious mechanical gadget that was discovered a century ago in a 2,000-year-old shipwreck.

Since it was found, the shoe-box-size device known as the Antikythera mechanism has amazed historians and other scholars with its advanced technology. The precision assembly contains 30 bronze gears with as many as 224 presumably hand-cut teeth.

Students of the mechanism, who have long known that it served as an astronomical computer, have deemed it to be at least 1,000 years more advanced than any other known mechanical device of its era. The remains of the apparatus consist of more than 80 congealed fragments of disintegrating metal adorned with cryptic inscriptions and entrusted with corrosion.

To make sense of that shattered structure, astronomer Michael G. Edmunds of Cardiff University in Wales and his colleagues have now applied two advanced imaging techniques to the shards. One is X-ray computer tomography, which records views of an object like those produced by a medical CT scanner. A high-power X-ray source penetrated the dense relic with a beam narrow enough to reveal fine details, says Andrew Ramsey, a tomography specialist with X-Tek Systems in Tring, England.

"The computer tomography images of the mechanism have literally opened the device up to us to see how it worked," comments ancient-astronomy scholar John M. Steele of the University of Durham in England.

The researchers also applied a novel computer-enhanced, optical-imaging technique for examining surface features.

Indeed, in the Nov. 30 Nature, the team of British, Greek, and American researchers reports that its fresh look at the mechanism has uncovered clear evidence of a previously suspected function: computing lunar and solar eclipses. The new images also doubled the number of inscriptions that could be read on the device's parts. The inscriptions indicated specific functions, not all of which had been known.

Furthermore, the work revealed a previously unrecognized lunar-motion feature, says filmmaker and mathematician Tony Freeth of Images First, a leader of the study.

The researchers used their new data to come up with a revised configuration for the machine's clockwork that uses 29 of the 30 known gears plus five hypothetical gears, four of which had been proposed previously by other researchers.

The new work is "an important advance" comments Michael T. Wright, an Antikythera-mechanism scholar and a retired curator of London's Science Museum.

In the issue of Nature containing the report, Francois Charette of Ludwig Maximilians University in Munich calls the model "highly seductive and convincing in all of its details."

Among such details is a proposed spiral dial at the lower-back section of the device. Around this dial, the motion of a hand indicates the solar and lunar eclipses during a period of 18 years. Wright adds that the Antikythera mechanism probably also employed long-lost ways to show the motions of planets.