ANTIKYTHERA Mechanism

[Bianca]

[Bianca]

Was the Antikythera Mechanism the world’s first computer?



by John Seabrook

May 14, 2007 




The main fragment of the Mechanism, found after two thousand years under water. Courtesy Antikythera Mechanism Research Project.

Related Links
 The Antikythera Mechanism
 


Antikythera Mechanism; Ancient Greece; Technology; Astronomy; Archeology; Price, Derek; Wright, Michael


In October, 2005, a truck pulled up outside the National Archeological Museum in Athens, and workers began unloading an eight-ton X-ray machine that its designer, X-Tek Systems of Great Britain, had dubbed the Bladerunner. Standing just inside the National Museum’s basement was Tony Freeth, a sixty-year-old British mathematician and filmmaker, watching as workers in white T-shirts wrestled the Range Rover-size machine through the door and up the ramp into the museum. Freeth was a member of the Antikythera Mechanism Research Project—a multidisciplinary investigation into some fragments of an ancient mechanical device that were found at the turn of the last century after two thousand years in the Aegean Sea, and have long been one of the great mysteries of science.

Freeth, a tall, taciturn man with a deep, rumbling voice, had been a mathematician at Bristol University, taking a Ph.D. in set theory, a branch of mathematical logic. He had drifted away from the academy, however, and spent most of his career making films, many of them with scientific themes. The Antikythera Mechanism, which he had first heard about some five years earlier, had rekindled his undergraduate love of math and logic and problem-solving, and he had all but abandoned his film career in the course of investigating it. He was the latest in a long line of men who have made solving the mystery of the Mechanism their life’s work. Another British researcher, Michael Wright, who has studied the Mechanism for more than twenty years, was coincidentally due to arrive in Athens before the Bladerunner had finished its work. But Wright wasn’t part of the research project, and his arrival was anticipated with some trepidation.

It had been Freeth’s idea to contact X-Tek in the hope of finding a high-resolution, three-dimensional X-ray technology to see inside the fragments of the Mechanism. As it happened, the company was working on a prototype of a CAT-scan machine that would use computer tomography to make 3-D X-rays of the blades inside airplane turbines, for safety inspections. Roger Hadland, X-Tek’s owner and chief engineer, was interested in Freeth’s proposal, and he and his staff developed new technology for the project.

After the lead-lined machine was installed inside the museum, technicians spent another day attaching the peripheral equipment. At last, everything was ready. The first piece to be examined, Fragment D, was placed on the Bladerunner’s turntable. It was only about an inch and a half around—much smaller than Fragment A, the largest piece, which measures about six and a half inches across—and it looked like just a small greenish rock, or possibly a lump of coral. It was heavily corroded and calcified—the parts of the Mechanism almost indistinguishable from the petrified sea slime that surrounded them. Conservationists couldn’t clean off any more of the corroded material without damaging the artifact, and it was hoped that the latest in modern technology would reveal the ancient technology inside.


from the issuecartoon banke-mail thisThe Bladerunner began to whirr. As the turntable rotated, an electron gun fired at a tungsten target, which emitted an X-ray beam that passed through the fragment, so that an image was recorded every time the turntable moved a tenth of a degree. A complete three-hundred-and-sixty-degree rotation, resulting in three thousand images or so, required about an hour. Then the computer required another hour to assemble all the images into a 3-D representation of what the fragment looked like on the inside.

As Freeth waited impatiently for the first images to appear on the Bladerunner’s monitor, he was trying not to hope for too much, and to place his trust in the skills of the group of academics and technicians who were there with him. Among them, waiting with equal anticipation, were John Seiradakis, a professor of astronomy at the Aristotle University of Thessaloniki; Xenophon Moussas, the director of the Astrophysics Laboratory at the University of Athens; and Yanis Bitsakis, a Ph.D. student in physics. (Mike Edmunds, an astrophysicist at Cardiff University, who was the academic leader of the research project, remained in Wales.) “I was just focussed on my relief that this was happening at all, with all the delays of the past four years,” Freeth told me. “Honestly, there were times when I thought it would never happen.”

One day in the spring of 1900, a party of Greek sponge divers returning from North Africa was forced by a storm to take shelter in the lee of the small island of Antikythera, which lies between Crete and Kythera. After the storm passed, one of the divers, Elias Stadiatis, put on a weighted suit and an airtight helmet that was connected by an air hose to a compressor on the boat, and went looking for giant clams, with which to make a feast that evening.

The bottom of the sea dropped sharply, and the diver followed the underwater cliff to a shelf that was about a hundred and forty feet below the surface. On the other side of the shelf, an abyss fell away into total darkness. Looking around, Stadiatis saw the remains of an ancient shipwreck. Then he had a terrible shock. There were piles of bodies, all in pieces, covering the ledge. He grabbed one of the pieces before surfacing in order to have proof of what he had seen. It turned out to be a bronze arm.

The following autumn, the sponge divers, now working for the Greek government, returned to the site, and over the next ten months they brought up many more pieces of sculpture, both marble and bronze, from the wreck, all of which were taken to the National Museum to be cleaned and reassembled. It was the world’s first large-scale underwater archeological excavation. Evidence derived from coins, amphorae, and other items of the cargo eventually allowed researchers to fix a date for the shipwreck: around the first half of the first century B.C., a time when the glorious civilization of ancient Greece was on the wane, following the Roman conquest of the Greek cities. Coins from Pergamum, a Hellenistic city in what is now Turkey, indicated that the ship had made port nearby. The style of the amphorae strongly suggested that the ship had called at the island of Rhodes, also on the eastern edge of the Hellenistic world, and known for its wealth and its industry. Given the reputed corruption of officials in the provinces of the Roman Empire, it is possible that the ship’s cargo had been plundered from Greek temples and villas, and was on its way to adorn the houses of aristocrats in Rome. The sheer weight of the cargo probably contributed to the ship’s destruction.

“Fragmentary Knowledge” continues
Page 1

[Bianca]

(page 2)

 
Most of the marble pieces were blackened and pitted from their long immersion in the salt water, but the bronze sculptures, though badly corroded, were salvageable. Although bronze sculptures were common in ancient Greece, only a tiny number have survived (the bronze was often sold as scrap, melted down, and recast, possibly as weaponry), and most of those have been recovered from shipwrecks. Among the works of art that emerged from the waters near Antikythera are the bronze portrait of a bearded philosopher, and the so-called Antikythera Youth, a larger-than-life-size naked young man: a rare specimen of a bronze masterwork, believed to be from the fourth century B.C.

Other artifacts included bronze fittings for wooden furniture, pottery, an oil lamp, and item 15087—a shoebox-size lump of bronze, which appeared to have a wooden exterior. Inside were what seemed to be fused metal pieces, but the bronze was so encrusted with barnacles and calcium that it was difficult to tell what it was. With so much early excitement focussed on the sculptures, the artifact didn’t receive much attention at first. But one day in May, 1902, a Greek archeologist named Spyridon Staïs noticed that the wooden exterior had split open, probably as a result of exposure to the air, and that the artifact inside had fallen into several pieces. Looking closely, Staïs saw some inscriptions, in ancient Greek, about two millimetres high, engraved on what looked like a bronze dial. Researchers also noticed precisely cut triangular gear teeth of different sizes. The thing looked like some sort of mechanical clock. But this was impossible, because scientifically precise gearing wasn’t believed to have been widely used until the fourteenth century—fourteen hundred years after the ship went down.

The first analyses of what became known as the Antikythera Mechanism followed two main approaches. The archeologists, led by J. N. Svoronos, of the National Museum, thought that the artifact must have been “a kind of astrolabe.” A Hellenistic invention, an astrolabe was an astronomical device that was widely known in the Islamic world by the eighth century and in Europe by the early twelfth century. Astrolabes were used to tell the time, and could also determine latitude with reference to the position of the stars; Muslim sailors often used them, in addition, to calculate prayer times and find the direction of Mecca.

However, other researchers, led by the German philologist Albert Rehm, thought that the Mechanism appeared much too complex to be an astrolabe. Rehm suggested that it might possibly be the legendary Sphere of Archimedes, which Cicero had described in the first century B.C. as a kind of mechanical planetarium, capable of reproducing the movement of the sun, the moon, and the five planets that could be seen from Earth without a telescope—Mercury, Venus, Mars, Jupiter, and Saturn. Still others, acknowledging the artifact’s complexity, thought that it must have come from a much later shipwreck, which may have settled on top of the ancient ship (even though the Mechanism had plainly been crushed under the weight of the ship’s other cargo). But, in the absence of any overwhelming evidence one way or the other, until the nineteen-fifties the astrolabe theory held sway.


from the issuecartoon banke-mail thisLooking back over the first fifty years of research on the Mechanism, one is struck by the reluctance of modern investigators to credit the ancients with technological skill. The Greeks are thought to have possessed crude wooden gears, which were used to lift heavy building materials, haul up water, and hoist anchors, but historians do not generally credit them with possessing scientifically precise gears—gears cut from metal and arranged into complex “gear trains” capable of carrying motion from one driveshaft to another. Paul Keyser, a software developer at I.B.M. and the author of “Greek Science of the Hellenistic Era,” told me recently, “Those scholars who study the history of science tend to focus on science beginning with Copernicus and Galileo and Harvey, and often go so far as to assert that no such thing existed before.” It’s almost as if we wished to reserve advanced technological accomplishment exclusively for ourselves. Our civilization, while too late to make the fundamental discoveries that the Greeks made in the sciences—Euclidean geometry, trigonometry, and the law of the lever, to name a few—has excelled at using those discoveries to make machines. These are the product and proof of our unique genius, and we’re reluctant to share our glory with previous civilizations.

In fact, there is evidence that earlier civilizations were much more technically adept than we imagine they were. As Peter James and Nick Thorpe point out in “Ancient Inventions,” published in 1994, some ancient civilizations were aware of natural electric phenomena and the invisible powers of magnetism (though neither concept was understood). The Greeks had a tradition of great inventors, beginning with Archimedes of Syracuse (c. 287-212 B.C.), who, in addition to his famous planetarium, is believed to have invented a terrible clawed device made up of large hooks, submerged in the sea, and attached by a cable to a terrestrial hoist; the device was capable of lifting the bow of a fully loaded warship into the air and smashing it down on the water—the Greeks reportedly used the weapon during the Roman siege of Syracuse around 212 B.C. Philon of Byzantium (who lived around 200 B.C.) made a spring-driven catapult. Heron of Alexandria (who lived around the first century A.D.) was the most ingenious inventor of all. He described the basic principles of steam power, and is said to have invented a steam-powered device in which escaping steam caused a sphere with two nozzles to rotate. He also made a mechanical slot machine, a water-powered organ, and machinery for temples and theatres, including automatic swinging doors. He is perhaps best remembered for his automatons—simulations of animals and men, cleverly engineered to sing, blow trumpets, and dance, among other lifelike actions.

“Fragmentary Knowledge” continues

[Bianca]

Dept. of Archeology
Fragmentary Knowledge

by John Seabrook (page 3)


Large Text Print E-Mail Feeds
Although a book by Heron, “Pneumatica,” detailing various of these inventions, has survived, some scholars have dismissed his descriptions as fantasy. They have pointed to the lack of evidence—no trace of any of these marvellous machines has been found. But, as other scholars have pointed out, the lack of archeological evidence isn’t really surprising. No doubt, the machines eventually broke down, and, as the know-how faded, there was no one around who could fix them, so they were sold as scrap and recycled. Very few technical drawings or writings remained, because, as Paul Keyser observes, “the texts that survive tend to be the more popular texts—i.e., those that were more often copied—and textbooks, not the research works or the advanced technical ones.” Eventually, following the dissolution of the Roman Empire, the technological knowledge possessed by the Greeks disappeared from the West completely.

But, if the Greeks did have greater technological sophistication than we think they did, why didn’t they apply it to making more useful things—time- and work-saving machines, for example—instead of elaborate singing automatons? Or is what we consider important about technology—which is, above all, that it is useful—different from what the Greeks considered worthwhile: amusement, enlightenment, delight for its own sake? According to one theory, the Greeks, because they owned slaves, had little incentive to invent labor-saving devices—indeed, they may have found the idea distasteful. Archimedes’ claws notwithstanding, there was, as Keyser notes, cultural resistance to making high-tech war machines, because “both the Greeks and the Romans valued individual bravery in war.” In any case, in the absence of any obvious practical application for Greek technology, it is easy to believe that it never existed at all.

In 1958, Derek de Solla Price, a fellow at the Institute for Advanced Study, in Princeton, went to Athens to examine the Mechanism. Price’s interests fell between traditionally defined disciplines. Born in Britain, he trained as a physicist but later switched fields and became the Avalon Professor of the History of Science at Yale; he is credited with founding Scientometrics, a method of measuring and analyzing the pursuit of science. The study of the Mechanism, which incorporates elements of archeology, astronomy, mathematics, philology, classical history, and mechanical engineering, was ideally suited to a polymath like Price, and it consumed the rest of his life.

Price believed that the Mechanism was an ancient “computer,” which could be used to calculate astronomical events in the near or distant future: the next full moon, for example. He realized that the inscriptions on the large dial were calendrical markings indicating months, days, and the signs of the zodiac, and postulated that there must have been pointers, now missing, that represented the sun and the moon and possibly the planets, and that these pointers moved around the dial, indicating the position of the heavenly bodies at different times.

Price set about proving these theories, basing his deductions on the fundamental properties of gearing. Gears work by transmitting power through rotational motion, and by realizing mathematical relationships between toothed gear wheels. The Mechanism concentrates on the latter aspect. Price seems to have assumed that the largest gear in the artifact, which is clearly visible in Fragment A, was tied to the movement of the sun—one rotation equalled one solar year. If another gear, representing the moon, was driven by the solar gear, then the ratio of wheels in this gear train must have been designed to match the Greeks’ idea of the moon’s movements. By counting the number of teeth in each gear, you could calculate the gear ratios, and, by comparing those ratios to astronomical cycles, you can figure out which gears represented which movements.


from the issuecartoon banke-mail thisHowever, because only a few of the gears appear at the surface of the Mechanism, and because many of the gear teeth are missing, Price had to develop methods for estimating total numbers from partial tooth counts. Finally, in 1971, he and a Greek radiographer, Dr. C. Karakalos, were permitted to make the first X-rays of the Mechanism, and these two-dimensional images showed almost all the remaining gear teeth. Price developed a schematic drawing of a hypothetical reconstruction of the internal workings of the Mechanism. In 1974, Price published his research in the form of a seventy-page monograph titled “Gears from the Greeks.” He had written, “Nothing like this instrument is preserved elsewhere. Nothing comparable to it is known from any ancient scientific text or literary allusion. On the contrary, from all that we know of science and technology in the Hellenistic Age we should have felt that such a device could not exist.”

Price expected his work on the Mechanism to change the history of technology. The Mechanism “requires us to completely rethink our attitudes toward ancient Greek technology,” he wrote, and later added, “It must surely rank as one of the greatest mechanical inventions of all time.” Price also pointed out that the Mechanism cannot have been the only one of its kind; no technology this sophisticated could have appeared suddenly, fully realized. Not only did the Mechanism demonstrate that our concept of ancient technology was fundamentally incomplete; it also contradicted the neo-Darwinian concept of technical progress in general as a gradual evolution toward ever greater complexity (technological history being the last refuge of the nineteenth-century belief in progress)—an idea firmly embedded in A. P. Usher’s classic 1929 study, “A History of Mechanical Inventions.” As Price writes, it is “a bit frightening to know that just before the fall of their great civilization the ancient Greeks had come so close to our age, not only in their thought, but also in their scientific technology.”

But Price’s work, though widely reviewed in scholarly journals, did not change the way the history of the ancient world is written. Otto Neugebauer’s huge “A History of Ancient Mathematical Astronomy,” which came out the year after “Gears,” relegates the Mechanism to a single footnote. Scholars and historians may have been reluctant to rewrite the history of technology to include research that had lingering doubts attached to it. Also, Price’s book was published at the height of the popularity of “Chariots of the Gods,” a 1968 book by the Swiss writer Erich von Däniken, which argued that advanced aliens had seeded the earth with technology, and Price got associated with U.F.O.s and crop circles and other kinds of fringe thinking. Finally, as Paul Keyser told me, “Classical scholarship is very literary, and focusses on texts—such as the writing of Homer, Sophocles, Virgil, or Horace, or it is old-fashioned and historical, and focusses on leaders and battles, through the texts of Herodotus and Thucydides, or it is anthropological-archeological, and focusses on population distributions and suchlike. So when an archeological discovery about ancient technology arrives, it does not fit, because it’s new, it’s scientific, and it’s not a text. Plus, there is only one such device, and unique items tend to worry scholars and scientists, who quite reasonably prefer patterns and larger collections of data.” Whatever the reason, as one scholar, Rob Rice, noted in a paper first presented in 1993, “It is neither facile nor uninstructive to remark that the Antikythera mechanism dropped and sank—twice”—once in the sea and once in scholarship.

“Fragmentary Knowledge” continues

[Bianca]

Dept. of Archeology
Fragmentary Knowledge
by John Seabrook (page 4)


The National Museum in Athens took no special pains in displaying the lumps of bronze. Item 15087 wasn’t much to look at. When the physicist Richard Feynman visited, in 1980, there was little information explaining what the Mechanism was. In a letter to his family, later published in the book “What Do You Care What Other People Think?,” the physicist wrote that he found the museum “slightly boring because we have seen so much of that stuff before. Except for one thing: among all those art objects there was one thing so entirely different and strange that it is nearly impossible. It was recovered from the sea in 1900 and is some kind of machine with gear trains, very much like the inside of a modern wind-up alarm clock.” When Feynman asked to know more about item 15087, the curators seemed a little disappointed. One said, “Of all the things in the museum, why does he pick out that particular item, what is so special about it?”

For the Greeks, as for other ancient civilizations, astronomy was a vital and practical form of knowledge. The sun and the moon were the basis for calendars by which people marked time. The solar cycle told farmers the best times for sowing and harvesting crops, while the lunar cycle was commonly used as the basis for civic obligations. And, of course, for mariners the stars provided some means of navigating at night.

Xenophon Moussas, one of the two Greek astronomers who are part of the research project, is a compact, soft-spoken man. He grew up in Athens, and as a boy, visiting the museum, he often pondered the Mechanism; now as a professor of astrophysics, he uses it to connect with his undergraduate students, for whom ancient technology is often more compelling than ancient theory.

One evening in January, Moussas led me on a memorable walk around the archeological park in central Athens, which includes both the Greek and the Roman agoras. As a quarter moon shone in the clear night sky, illuminating the ruined temples and markets, Moussas narrated the story of how the ancients slowly learned to recognize patterns and serial events in the movements of the stars, and to use them to tell time and to predict future astronomical events. “It was a way of keeping track not of time as we think of it,” he told me, “but of the movement of the stars—a deeper time.”

For the Greeks, like the Babylonians before them, the year consisted of twelve “lunations,” or new-moon-to-new-moon cycles, each of which lasted an average of twenty-nine and a half days. The problem with a lunar calendar is that twelve lunar cycles takes about eleven days less than one solar cycle. That means that if you don’t make regular adjustments to the calendar the seasons soon slip out of synch with the months, and after eighteen years or so the summer solstice will occur in December. Finding a system that reconciled the lunar year with the solar year was the great challenge of calendar-making.


from the issuecartoon banke-mail thisMost ancient societies readjusted their calendars by adding a thirteenth, “intercalary” month every three years or so, although methods of calculating the length of these months, and when they should be added, were never precise. Babylonian astronomers hit upon an improvement. They discovered that there are two hundred and thirty-five lunar months in nineteen years. In other words, if you observe a full moon on April 4th, there will be another full moon in that same place on April 4th nineteen years later. This cycle, which eventually came to be known as the Metonic cycle, after the Greek astronomer Meton of Athens, was an extremely useful tool for keeping the lunar calendar and the solar calendar in synch. (The Metonic cycle is still used by the Christian Churches to calculate the correct day for celebrating Easter.) The Babylonians also established what would come to be known as the saros cycle, which is a way of predicting the likely occurrence of eclipses. Babylonian astronomers observed that eighteen years, eleven days, and eight hours after an eclipse a nearly identical eclipse will occur. Eclipses were believed by many ancient societies to be omens that, depending on how they were interpreted, could foretell the future of a monarch, for example, or the outcome of a military campaign.

The Greeks, in turn, discovered the Callippic cycle, which consisted of four Metonic cycles minus one day, and was an even more precise way to reconcile the cycles of the sun and the moon. But the Greeks’ real genius was to work out theories to explain these cycles. In particular, they brought the concept of geometry to Babylonian astronomy. As Alexander Jones, a professor of classics at the University of Toronto, put it to me recently, “The Greeks saw the Babylonian formulas in terms of geometry—they saw all these circles all spinning around each other in the sky. And of course this fits in perfectly with the concept of gearworks—the gears are making little orbits.” Some Greek inventor must have realized that it was possible to build a simulation of the movements in the heavens by reproducing the cycles with gears.

But who? Price called the inventor simply “some unknown ingenious mechanic.” Others have speculated that the inventor was Hipparchus, the greatest of all ancient Greek astronomers. Hipparchus, who is also believed to have invented trigonometry, lived on the island of Rhodes from about 140 to 120 B.C. He detailed a theory to explain the anomalous movements of the moon, which appears to change speed during its orbit of the Earth. Hipparchus is also thought to have founded a school on Rhodes that was maintained after his death by Posidonius, with whom Cicero studied in 79 B.C. In one of his letters, Cicero mentions a device “recently constructed by our friend Posidonius,” which sounds very like the Mechanism, and “which at each revolution reproduces the same motions of the sun, the moon, and the five planets that take place in the heavens every day and night.”

“Fragmentary Knowledge” continues

[Bianca]

Fragmentary Knowledge
by John Seabrook (page 5)


As Moussas and I headed uphill, toward the Acropolis, he pointed out the spot where Meton’s astronomy school and solar observatory had been. On our way back down, we stopped at the famous Tower of the Winds, the now gutted shell of what was the great central clock of ancient Athens. Designed by the renowned astronomer Andronicus of Cyrrhus, it is thought to have been an elaborate water clock on the inside and a sundial on the outside. “But, in light of what we know about the Mechanism,” Moussas said, “I am beginning to wonder whether this was a much more complicated clock than we think.”

When Derek Price died, of a heart attack, in 1983, his work on the Mechanism was unfinished. Although his fundamental insights about the device were sound, he hadn’t figured out all the details, nor had he succeeded in producing a working model that was correct in all aspects.

That year, in London, a Lebanese man walked into the Science Museum, on Exhibition Road, with an ancient geared mechanism wrapped in a handkerchief in his pocket. Michael Wright, one of the curators of mechanical engineering, was summoned to examine the artifact, which was in four main fragments. The man said that he’d bought the artifact in a street market in Beirut several weeks earlier. The Science Museum eventually bought it from him, and Wright and a colleague, J. Field, showed that it was a geared sundial calendar that displayed the positions of the sun and the moon in the zodiac. Wright also built a reconstruction of the sundial. The style of lettering on the dial dated the device to the sixth century A.D., making it the second-oldest geared device ever found, after the Antikythera Mechanism.

In addition to his job as a curator, Wright helped to maintain the old clocks exhibited in the museum. Among them was a replica of the oldest clock that we have a clear account of, constructed in the early fourteenth century by Richard of Wallingford, the Abbot of St. Albans. It was a fantastic astronomical device called the Albion (“All-by-One”). Another reconstruction was of a famous planetarium and clock built by Giovanni de’ Dondi, of Padua, in the mid-fourteenth century, known as the Astrarium. Like many students of mechanical history, Wright had noted this odd upwelling of clockwork in Europe, appearing in several places at around the same time. He was familiar with the theory that many of the elements of clockwork were known to the ancients. With the decline of the West, goes this theory, technical expertise passed to the Islamic world, just as many of the Greek texts were translated into Arabic and therefore preserved from loss or destruction. In the ninth century, the Banu Musa brothers, in Baghdad, published the “Book of Ingenious Devices,” which detailed many geared mechanical contrivances, and the tenth-century philosopher and astronomer al-Biruni (973-1048) describes a Box of the Moon—a mechanical lunisolar calendar that used eight gearwheels. The more Wright looked into these old Islamic texts, the more convinced he became that the ancient Greeks’ knowledge of gearing had been kept alive in the Islamic world and reintroduced to the West, probably by Arabs in thirteenth-century Spain.


from the issuecartoon banke-mail thisIn the course of this research, Wright became intensely interested in the Antikythera Mechanism. Upon studying Price’s account closely, he realized that Price had made several fundamental errors in the gearing. “I could see right away that Price’s reconstruction doesn’t explain what we can see,” he told me. “The man who made the Mechanism made no mistakes. He went straight to what he wanted, in the simplest way possible.” Wright resolved to complete Price’s work, and to build a working model of the Mechanism.

Whereas Price worked mainly on an academic level, approaching the Mechanism from the perspective of mathematical and astronomical theory, Wright drew on his vast practical knowledge of arbors, crown wheels, and other mechanical techniques used in gear-train design. His experience in repairing old grandfather clocks, many of which also have astronomical displays that show the phases of the moon, led him to one of his key insights into the engineering of the Mechanism. He posited that there must have been a revolving ball built in the front dial that indicated the phases of the moon—one hemisphere was black, the other white, and the ball rotated as the moon waxed or waned. Wright also showed how a pin-and-slot construction could be used to model the movement of the moon.

Wright, who is fifty-eight, has a British public-school demeanor, which is generally courteous and hearty and seemingly rational. But he is prey to dark moods, wild, impolitic outbursts, and overcomplicated personal entanglements—“muddles,” he calls them. Although he told me, “I really hate confrontation, and antagonism of any kind, even competition,” he consistently finds himself in disastrous confrontations with people who should be his allies. Whereas academic researchers are used to collaboration, and to sharing resources and insights, Wright is temperamentally more like a lone inventor, working away in secrecy and solitude until he has found the solution.

He did have a collaborator once—Allan Bromley, a lecturer in computer science at the University of Sydney and an expert on Charles Babbage, the nineteenth-century British mathematician who was the first to conceive of the programmable computer. Bromley used to come to the Science Museum to study Babbage’s papers and drawings and Wright would often lunch with him. In 1990, the pair took new X-rays of the Mechanism, the first since Price’s. But Bromley brought the data back to Sydney and would allow Wright to see only small portions of the material. (According to Wright, Bromley confessed “that he had it fixed in his mind that it would be his name, preferably alone, that would be attached to the ‘solution.’ ”)

 

[Bianca]

Dept. of Archeology
Fragmentary Knowledge

by John Seabrook (page 6)



Meanwhile, Wright got into a muddle with his boss at the Science Museum, an “out-and-out bully” who would allow Wright to work on the Mechanism only in his free time. (“We don’t do the ancient world,” Wright remembers another colleague saying.) This meant that while Wright’s wife would go on holiday with their children, Wright would go to the museum in Athens. (Eventually, after years of this routine, he and his wife divorced.)

By the late nineteen-nineties, Bromley was dying of cancer. Wright went to see him in Sydney, and Bromley turned much of the data over to him. Just as Wright was finally able to work up their findings for publication, however, he learned of the research project and the effort to take a new set of X-rays of the Mechanism. Instead of viewing this new investigation as a potential boon, he saw it as an improper encroachment on his own turf. “There is a long-established unwritten law concerning the study of Greek antiquities, which is that when one researcher has access to the material, any other researcher is denied access until the first has finished,” he wrote to me. “In my case, this understanding was swept aside through the machinations of the group.” So, when he arrived at the National Museum while the Bladerunner’s X-rays were in progress, he was not excited, like the others; he was “angry, tired, and depressed.”

The first images of Fragment D to appear on the Bladerunner’s monitor were stunning—“so much better than we dared to hope,” Freeth told me. “They took your breath way.” Inside the corroded rock was what looked like a geared embryo—the incipient bud of an industrial age that remained unborn for a millennium.

Then the team spotted an oddlooking inscription. Andrew Ramsey, X-Tek’s computer-tomography specialist, who was operating the viewer, zoomed around inside the 3-D representation until he found the right slice. Written on the side of the gear were the letters “M” and “E”—“ME.” Was this the maker’s mark? Or could “ME” mean “Part 45”? (“ME” is the symbol for forty-five in ancient Greek.) Freeth joked that Mike Edmunds had scratched his initials on the fragment. Others suggested that this particular piece of the Mechanism could have been recycled, and that the “ME” was left over from some earlier device.

Altogether, the team salvaged about a thousand new letters and inscriptions from the Mechanism—doubling the number available to Price. Together with earlier imaging, the new inscriptions support theories that both Price and Wright had advanced. On Fragment E, for example, the group read “235 divisions on the spiral.” “I was amazed,” Freeth said. “This completely vindicated Price’s idea of the Metonic cycle of two hundred and thirty-five lunar months on the upper back dial.” They also read words explaining that on the extremity of “the pointer stands a little golden sphere,” which probably refers to a representation of the sun on the sun pointer that went around the zodiac dial at the front of the Mechanism. Wright had proposed that the rings of the back dials were made in the form of spirals; the word eliki, meaning “spiral,” can be seen on Fragment E. On Fragment 22, the number “223” has been observed, pointing to the use of the saros dial as an eclipse indicator.


It was, as Xenophon Moussas put it to me, as if “we had discovered the user’s manual, right inside the machine.” What had been regarded mainly as an archeological artifact took on a different sort of artifactual status, as an important astronomical text. Very few copies of original astronomical texts remain from the period; most of our knowledge about ancient astronomy comes from other, later astronomers. Little of Hipparchus’ writing survives; we rely largely on Ptolemy of Alexandria, who some believe took much of Hipparchus’ work and called it his own.

Many of the inscriptions took months to read. Yanis Bitsakis, the Ph.D. student, collaborated with Freeth and the X-Tek team in rendering the X-ray data as computer images, while Agamemnon Tselikas, a leading Greek paleographer, did all the readings and most of the translations. As Bitsakis explained to me, “One of the difficulties in reading the texts was that in ancient Greek there were no spaces between the words, and there are many alternative readings. Also, in many cases the edges of the lines are missing, so we don’t know what is continuous text.” He and Tselikas would work on the readings through the night, frequently e-mailing and calling other members of the team about new discoveries. Moussas remembers this period, lasting until the spring of 2006, as “the most interesting time in my life.” For example, finding the words “sphere” and “cosmos” was extremely moving, Moussas told me: “I felt as though I were communicating with an ancient colleague, through the Mechanism.”

One day last month, I paid a visit to Michael Wright, in his book-and-clock-cluttered home, in West London. Wright was reading Xenophon, the Greek historian, in ancient Greek. He put the book down and brought out his model of the Mechanism from a cabinet underneath the stairs. In size, it is startlingly similar to a laptop computer, though a bit thicker. On the front dial, in addition to the pointers for the sun and the moon that Price posited, Wright added pointers for the planets and a separate pointer for the day of the year. On the back dial were two hundred and twenty-three divisions, marking months in the soros cycle; a similar dial above that showed months in the Metonic cycle. The gears were hidden inside a wooden casing, which had a large wooden knob on one side.

“Fragmentary Knowledge”
| Last >

[Bianca]

(page 7)

 
Wright was still a little upset about what he considered the sweeping claims that the research group had made when it published its findings, in the November 30, 2006, issue of Nature. He almost stayed home from the two-day conference on the Mechanism that the group put on, in early December. In the end, he decided to go, taking his wife, Anne, whom he married in 1998, “to stop me from lifting my knee in some chap’s groin.”

We went upstairs to Wright’s workshop. It was filled with tools and pieces of metal, and the air held the pleasantly acrid scent of machine oil. Scattered across the tables and the floor were clever devices that Wright had fashioned out of gears—clocks, astrolabes, engines of various kinds. I recalled Price’s description of the maker of the Mechanism—“some unknown ingenious mechanic”—and wondered if this mysterious maker might have been a bit like Wright, with a workshop similarly cluttered with machines.

Wright took his model apart and showed me how all the gears fitted together. I noticed some writing on a rectangular metal plate in the middle of the mechanism, and Wright told me that it was made of recycled bits of brass left over from some previous incarnation.

“So you think that the letters ‘ME’—”

“Precisely,” Wright interjected. “I think they must relate to whatever that bit of metal was used for before.”

Then Wright put the machine back together and turned the hand knob that drives the solar gear. It engaged with the smaller gears, through the various gear trains, and the pointers began to spin around the dials. The day-of-the-year pointer moved forward at a regular pace, but the lunar and planetary pointers traced eccentric orbits, sometimes reversing course and going backward, just as the planets occasionally appear to do in the night sky. Meanwhile, the pointers on the back dials crept through the months in the saros and Metonic cycles; eclipses came and went. I noticed that as long as he kept turning the knob Wright himself seemed, for once, perfectly unmuddled.

Until this moment, I had, like many others, continued to puzzle over why, if the Greeks were capable of building such a technically sophisticated device, they used that capacity to construct what is essentially a toy—an intellectual amusement. But as I beheld this whirring, whirling symphony of metal, a perfect simulation of a mechanistic and logical universe, I realized that my notions of practicality were foolish and shortsighted. This machine was much more than a toy; it embodied a whole world view, and it must have been, for the ancients, wonderfully reassuring to behold. ♦

[Bianca]

[Bianca]

[Bianca]

 
News Feature
 
 
Nature
Published online: 29 November 2006; | doi:10.1038/444534a
In search of lost time
The ancient Antikythera Mechanism doesn't just challenge our assumptions about technology transfer over the ages — it gives us fresh insights into history itself.
Jo Marchant

 
 
 
It looks like something from another world — nothing like the classical statues and vases that fill the rest of the echoing hall. Three flat pieces of what looks like green, flaky pastry are supported in perspex cradles. Within each fragment, layers of something that was once metal have been squashed together, and are now covered in calcareous accretions and various corrosions, from the whitish tin oxide to the dark bluish green of copper chloride. This thing spent 2,000 years at the bottom of the sea before making it to the National Archaeological Museum in Athens, and it shows.



 
J. MARCHANT/ANTIKYTHERA MECHANISM RESEARCH PROJECT
 
But it is the details that take my breath away. Beneath the powdery deposits, tiny cramped writing is visible along with a spiral scale; there are traces of gear-wheels edged with jagged teeth. Next to the fragments an X-ray shows some of the object's internal workings. It looks just like the inside of a wristwatch.

This is the Antikythera Mechanism. These fragments contain at least 30 interlocking gear-wheels, along with copious astronomical inscriptions. Before its sojourn on the sea bed, it computed and displayed the movement of the Sun, the Moon and possibly the planets around Earth, and predicted the dates of future eclipses. It's one of the most stunning artefacts we have from classical antiquity.

No earlier geared mechanism of any sort has ever been found. Nothing close to its technological sophistication appears again for well over a millennium, when astronomical clocks appear in medieval Europe. It stands as a strange exception, stripped of context, of ancestry, of descendants.

Considering how remarkable it is, the Antikythera Mechanism has received comparatively scant attention from archaeologists or historians of science and technology, and is largely unappreciated in the wider world. A virtual reconstruction of the device, published by Mike Edmunds and his colleagues in this week's Nature (see 'Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism'), may help to change that. With the help of pioneering three-dimensional images of the fragments' innards, the authors present something close to a complete picture of how the device worked, which in turn hints at who might have been responsible for building it.

But I'm also interested in finding the answer to a more perplexing question — once the technology arose, where did it go to? The fact that such a sophisticated technology appears seemingly out of the blue is perhaps not that surprising — records and artefacts from 2,000 years ago are, after all, scarce. More surprising, to an observer from the progress-obsessed twenty-first century, is the apparent lack of a subsequent tradition based on the same technology — of ever better clockworks spreading out round the world. How can the capacity to build a machine so magnificent have passed through history with no obvious effects?
 
 
To get an idea of what the mechanism looked like before it had the misfortune to find itself on a sinking ship, I went to see Michael Wright, a curator at the Science Museum in London for more than 20 years and now retired. Stepping into Wright's workshop in Hammersmith is a little like stepping into the workshop where H. G. Wells' time machine was made. Every inch of floor, wall, shelf and bench space is covered with models of old metal gadgets and devices, from ancient Arabic astrolabes to twentieth-century trombones. Over a cup of tea he shows me his model of the Antikythera Mechanism as it might have been in its pomp. The model and the scholarship it embodies have consumed much of his life (see 'Raised from the depths').

The mechanism is contained in a squarish wooden case a little smaller than a shoebox. On the front are two metal dials (brass, although the original was bronze), one inside the other, showing the zodiac and the days of the year. Metal pointers show the positions of the Sun, the Moon and five planets visible to the naked eye. I turn the wooden knob on the side of the box and time passes before my eyes: the Moon makes a full revolution as the Sun inches just a twelfth of the way around the dial. Through a window near the centre of the dial peeks a ball painted half black and half white, spinning to show the Moon's changing phase.

On the back of the box are two spiral dials, one above the other. A pointer at the centre of each traces its way slowly around the spiral groove like a record stylus. The top dial, Wright explains, shows the Metonic cycle — 235 months fitting quite precisely into 19 years. The lower spiral, according to the research by Edmunds and his colleagues, was divided into 223, reflecting the 223-month period of the Saros cycle, which is used to predict eclipses.

 It's a popular notion that technological development is a simple progression. But history is full of surprises. 

 
To show me what happens inside, Wright opens the case and starts pulling out the wheels. There are 30 known gear-wheels in the Antikythera Mechanism, the biggest taking up nearly the entire width of the box, the smallest less than a centimetre across. They all have triangular teeth, anything from 15 to 223 of them, and each would have been hand cut from a single sheet of bronze. Turning the side knob engages the big gear-wheel, which goes around once for every year, carrying the date hand. The other gears drive the Moon, Sun and planets and the pointers on the Metonic and Saros spirals.

To see the model in action is to want to find out who had the ingenuity to design the original. Unfortunately, none of the copious inscriptions is a signature. But there are other clues. Coins found at the site by Jacques Cousteau in the 1970s have allowed the shipwreck to be dated sometime shortly after 85 BC. The inscriptions on the device itself suggest it might have been in use for at least 15 or 20 years before that, according to the Edmunds.
 
 
The ship was carrying a rich cargo of luxury goods, including statues and silver coins from Pergamon on the coast of Asia Minor and vases in the style of Rhodes, a rich trading port at the time. It went down in the middle of a busy shipping route from the eastern to western Aegean, and it seems a fair bet that it was heading west for Rome, which had by that time become the dominant power in the Mediterranean and had a ruling class that loved Greek art, philosophy and technology.
 
 
The Rhodian vases are telling clues, because Rhodes was the place to be for astronomy in the first and second centuries BC. Hipparchus, arguably the greatest Greek astronomer, is thought to have worked on the island from around 140 BC until his death in around 120 BC. Later the philosopher Posidonius set up an astronomy school there that continued Hipparchus' tradition; it is within this tradition that Edmunds and his colleagues think the mechanism originated. Circumstantial evidence is provided by Cicero, the first-century BC Roman lawyer and consul. Cicero studied on Rhodes and wrote later that Posidonius had made an instrument "which at each revolution reproduces the same motions of the Sun, the Moon and the five planets that take place in the heavens every day and night". The discovery of the Antikythera Mechanism makes it tempting to believe the story is true.

And Edmunds now has another reason to think the device was made by Hipparchus or his followers on Rhodes. His team's three-dimensional reconstructions of the fragments have turned up a new aspect of the mechanism that is both stunningly clever and directly linked to work by Hipparchus.

One of the wheels connected to the main drive wheel moves around once every nine years. Fixed on to it is a pair of small wheels, one of which sits almost — but not exactly — on top of the other. The bottom wheel has a pin sticking up from it, which engages with a slot in the wheel above. As the bottom wheel turns, this pin pushes the top wheel round. But because the two wheels aren't centred in the same place, the pin moves back and forth within the upper slot. As a result, the movement of the upper wheel speeds up and slows down, depending on whether the pin is a little farther in towards the centre or a little farther out towards the tips of the teeth (see illustration on 'Archaeology: High tech from Ancient Greece').

The researchers realized that the ratios of the gear-wheels involved produce a motion that closely mimics the varying motion of the Moon around Earth, as described by Hipparchus. When the Moon is close to us it seems to move faster. And the closest part of the Moon's orbit itself makes a full rotation around the Earth about every nine years. Hipparchus was the first to describe this motion mathematically, working on the idea that the Moon's orbit, although circular, was centred on a point offset from the centre of Earth that described a nine-year circle. In the Antikythera Mechanism, this theory is beautifully translated into mechanical form. "It's an unbelievably sophisticated idea," says Tony Freeth, a mathematician who worked out most of the mechanics for Edmunds' team. "I don't know how they thought of it."

"I'm very surprised to find a mechanical representation of this," adds Alexander Jones, a historian of astronomy at the University of Toronto, Canada. He says the Antikythera Mechanism has had little impact on the history of science so far. "But I think that's about to change. This was absolutely state of the art in astronomy at the time."

Wright believes that similar mechanisms modelled the motions of the five known planets, as well as of the Sun, although this part of the device has been lost. As he cranks the gears of his model to demonstrate, and the days, months and years pass, each pointer alternately lags behind and picks up speed to mimic the astronomical wanderings of the appropriate sphere.

Greek tragedy

Almost everyone who has studied the mechanism agrees it couldn't have been a one-off — it would have taken practice, perhaps over several generations, to achieve such expertise. Indeed, Cicero wrote of a similar mechanism that was said to have been built by Archimedes. That one was purportedly stolen in 212 BC by the Roman general Marcellus when Archimedes was killed in the sacking of the Sicilian city of Syracuse. The device was kept as an heirloom in Marcellus' family: as a friend of the family, Cicero may indeed have seen it.

So where are the other examples? A model of the workings of the heavens might have had value to a cultivated mind. Bronze had value for everyone. Most bronze artefacts were eventually melted down: the Athens museum has just ten major bronze statues from ancient Greece, of which nine are from shipwrecks. So in terms of the mechanism, "we're lucky we have one", points out Wright. "We only have this because it was out of reach of the scrap-metal man."

But ideas cannot be melted down, and although there are few examples, there is some evidence that techniques for modelling the cycles in the sky with geared mechanisms persisted in the eastern Mediterranean. A sixth-century AD Byzantine sundial brought to Wright at the Science Museum has four surviving gears and would probably have used at least eight to model the positions of the Sun and Moon in the sky. The rise of Islam saw much Greek work being translated into Arabic in the eighth and ninth centuries AD, and it seems quite possible that a tradition of geared mechanisms continued in the caliphate. Around AD 1000, the Persian scholar al-Biruni described a "box of the Moon" very similar to the sixth-century device. There's an Arabic-inscribed astrolabe dating from 1221–22 currently in the Museum of the History of Science in Oxford, UK, which used seven gears to model the motion of the Sun and Moon.

But to get anything close to the Antikythera Mechanism's sophistication you have to wait until the fourteenth century, when mechanical clockwork appeared all over western Europe. "You start to get a rash of clocks," says Wright. "And as soon as you get clocks, they are being used to drive astronomical displays." Early examples included the St Albans clock made by Richard Wallingford in around 1330 and a clock built by Giovanni de'Dondi a little later in Padua, Italy, both of which were huge astronomical display pieces with elaborate gearing behind the main dial to show the position of the Sun, Moon, planets and (in the case of the Padua clock) the timing of eclipses. The time-telling function seems almost incidental.

It could be argued that the similarities between the medieval technology and that of classical Greece represent separate discoveries of the same thing — a sort of convergent clockwork evolution. Wright, though, favours the idea that they are linked by an unbroken tradition: "I find it as easy to believe that this technology survived unrecorded, as to believe that it was reinvented in so similar a form." The timing of the shift to the West might well have been driven by the fall of Baghdad to the Mongols in the thirteenth century, after which much of the caliphate's knowledge spread to Europe. Shortly after that, mechanical clocks appeared in the West, although nobody knows exactly where or how. It's tempting to think that some mechanisms, or at least the ability to build them, came west at the same time. As François Charette, a historian of science at Ludwig Maximilians University in Munich, Germany, points out, "for the translation of technology, you can't rely solely on texts". Most texts leave out vital technical details, so you need skills to be transmitted directly.

But if the tradition of geared mechanisms to show astronomical phenomena really survived for well over a millennium, the level of achievement within that tradition was at best static. The clockwork of medieval Europe became more sophisticated and more widely applied fairly quickly; in the classical Mediterranean, with the same technology available, nothing remotely similar happened. Why didn't anyone do anything more useful with it in all that time? More specifically, why didn't anyone work out earlier what the gift of hindsight seems to make obvious — that clockwork would be a good thing to make clocks with?

Serafina Cuomo, a historian of science at Imperial College, London, thinks that it all depends on what you see as 'useful'. The Greeks weren't that interested in accurate timekeeping, she says. It was enough to tell the hour of the day, which the water-driven clocks of the time could already do fairly well. But they did value knowledge, power and prestige. She points out that there are various descriptions of mechanisms driven by hot air or water — and gears. But instead of developing a steam engine, say, the devices were used to demonstrate philosophical principles. The machines offered a deeper understanding of cosmic order, says David Sedley, a classicist at the University of Cambridge, UK. "There's nothing surprising about the fact that their best technology was used for demonstrating the laws of astronomy. It was deep-rooted in their culture."

Another, not mutually exclusive, theory is that devices such as the Antikythera Mechanism were signifiers of social status. Cuomo points out that demonstrating wondrous devices brought social advancement. "They were trying to impress their peers," she says. "For them, that was worth doing." And the Greek élite was not the only potential market. Rich Romans were eager for all sorts of Greek sophistication — they imported philosophers for centuries.

 I find it as easy to believe that this technology survived unrecorded, as to believe that this was reinvented in so similar a form. 

Michael Wright
 
 
 
 
Seen in this light, the idea that the Antikythera Mechanism might be expected to lead to other sorts of mechanism seems less obvious. If it already embodied the best astronomy of the time, what more was there to do with it? And status symbols do not follow any clearly defined arc of progress. What's more, the idea that machines might do work may have been quite alien to slave-owning societies such as those of Ancient Greece and Rome. "Perhaps the realization that you could use technology for labour-saving devices took a while to dawn," says Sedley.

There is also the problem of power. Water clocks are thought to have been used on occasion to drive geared mechanisms that displayed astronomical phenomena. But dripping water only provides enough pressure to drive a small number of gears, limiting any such display to a much narrower scope than that of the Antikythera Mechanism, which is assumed to have been handcranked. To make the leap to mechanical clocks, a geared mechanism needs to be powered by something other than a person; it was not until medieval Europe that clockwork driven by falling weights makes an appearance.

Invention's evolution

Bert Hall, a science historian at the University of Toronto in Canada, believes a final breakthrough towards a mechanical weight drive might have come about almost by accident, by adapting a bell-ringing device. A water clock could have driven a hammer or weight mechanism swinging between two bells as an alarm system, until someone realized that the weight mechanism would be a more regular way of driving the clock in the first place. When the new way to drive clocks was discovered, says Hall, "the [clockwork] technology came rushing out of the wings into the new tradition".

Researchers would now love further mechanisms to be unearthed in the historical record. "We hope that if we can bring this to people's attention, maybe someone poking around in their museum might find something, or at least a reference to something," says Edmunds. Early Arabic manuscripts, only a fraction of which have so far been studied, are promising to be fertile ground for such discoveries.

Charette also hopes the new Antikythera reconstruction will encourage scholars to take the device more seriously, and serve as a reminder of the messy nature of history. "It's still a popular notion among the public, and among scientists thinking about the history of their disciplines, that technological development is a simple progression," he says. "But history is full of surprises.
 
 
In the meantime, Edmunds' Antikythera team plans to keep working on the mechanism — there are further inscriptions to be deciphered and the possibility that more fragments could be found. This week the researchers are hosting a conference in Athens that they hope will yield fresh leads. A few minutes' walk from the National Archaeological Museum, Edmunds' colleagues from the University of Athens, Yanis Bitsakis and Xenophon Moussas, treat me to a dinner of aubergine and fried octopus, and explain why they would one day like to devote an entire museum to the story of the fragments.

"It's the same way that we would do things today, it's like modern technology," says Bitsakis. "That's why it fascinates people." What fascinates me is that where we see the potential of that technology to measure time accurately and make machines do work, the Greeks saw a way to demonstrate the beauty of the heavens and get closer to the gods.


Jo Marchant is Natures News Editor.

Article brought to you by: Nature
 
 
 
 
 

[Bianca]

 

[Bianca]

[Bianca]

                                    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.

                                         

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.

[Bianca]

                                  

                                                       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.

John Gleave can be reached at:-
Tel & Fax 01422 844837