Salamis Tablet - Journal of Computer History

The Antikythera Mechanism and the History of Clockwork

In the early autumn of 1900, Captain Dimitrios Kontos and his crew took shelter from a storm on the small, barren island of Antikythera - located on the southern periphery of the Aegean Sea, between Crete and Peloponnese.

The crew was an intrepid bunch made up of six sponge divers and 20 oarsmen on two small vessels. Deep sea diving at the turn of the twentieth century was a physically challenging and dangerous affair. The suits were made from layers of thick canvas sealed with rubber, topped by a copper helmet so heavy it took two men to place it over the diver's head. Fresh air was pushed to the suit through a flexible hose by a compressor on a ship at the surface. Decompression sickness ("the bends"), although poorly understood, was a painful and frequently life-shortening reality for the divers.

Kontos and his crew were returning from an expedition to the sponge fields of Northern Africa when the storm hit. Once the weather had settled some, they decided to take advantage of the forced detour and explore the waters off the coast of the island in search of sponges to harvest.

What they found instead was the site of an ancient shipwreck. A novelty at the time, the Antikythera Wreck became the subject of history's first major underwater archaeological excavation. Artifacts recovered from the wreck included marble and bronze statuary, amphoras, jewelry, lamps, glasswork and tools. Among the artifacts was a small "lump" of corroded bronze and wood that at first went unnoticed as it was brought to the National Archaeological Museum in Athens and placed in storage.

It would be several years before archaeologist Valerios Stais noticed that the artifact had a gear wheel embedded in it. It then take more than a century for archaeologists, historians, astronomers and mathematicians to unravel its mysteries.

The Antikythera Mechanism, as the artifact would come to be called, is a wonder of engineering. The device is part celestial calculator and part orrey - a mechanical model of the solar system. Roughly the size and appearance of a table clock with dial faces on the front and back, it features about 30 inter-meshing gears operated by turning a hand crank. Among its many capabilities, the Antikythera Mechanism could calculate and display planetary movement and accurately predict eclipses centuries into the future.

In addition to the technological mastery it displays the mechanism reinforces the primacy of astronomy, not only in the daily lives of the Ancient Greeks, but through their math, science and philosophy as well. From the perspective of the historian it only makes sense that the Ancient Greeks' greatest technological achievement would be an astronomical clock.

There's one aspect of Antikythera Mechanism that stands out above all else. By conventional wisdom, it shouldn't exist. It would have been only slightly more wondrous for Kontos' divers to have returned with an Ancient Greek steam engine.

There are no other artifacts to imply that the Greeks had come anywhere close to this level of technology. The dating of the wreck is somewhat imprecise, but most experts place it somewhere between 200-100 BC. It would be more than 1,000 before a similar device appears in the written record of the Islamic world, and closer to 1,500 years until clockworks (complex geared mechanisms) at this level are seen in Europe.

The discovery of the Antikythera Mechanism, and the century-long effort to decipher its function, has led to a re-examination of the history of clockwork and its role in the development of mathematics and computation. Derek J. de Solla Price was a physicist and science historian who studied the Antikythera Mechanism extensively from the 1950s until his death in 1983. Price and fellow physicist Charalambos Karakalos conducted the first x-ray study of the device revealing its true complexities. Price began piecing together the theory that the device was a celestial calculator and working out its basic function. Although more recent research has refined our understanding, and sometimes rewritten the subtleties, much of Price's primary work on the device still stands.

As a science historian with a keen interest in the origins of clocks and scientific instruments, Price saw in the mechanism evidence of possible connections among the various ancient cultures and their technologies. Price's expanded view of the early history of gears and clockwork are examined in such papers as On the Origin of Clockwork, Perpetual Motion Devices, and the Compass published by the Smithsonian Institution in 1959.

Clockwork was one of the fundamental technologies propelling automated computation from the time of Pascal's seventeenth century invention of the Pascaline until the emergence of electronic computers in the mid-twentieth century. However, despite the work of Price and other science historians before and since, surprisingly little is known about the origins of geared mechanisms as tools for measurement and calculation.

The earliest reference to a geared mechanism with usefulness beyond the raw transmission of power is generally considered to be the Chinese South Pointing Chariot, attributed in ancient texts as an invention of the Yellow Emperor ca. 2600 BC. There is significant doubt that a real device existed that early, but South Pointing Chariots then appear throughout Chinese history, with the first authenticated reference being much later in the third century AD during the Jin Dynasty. The basic functionality was a two-wheeled chariot with the statue of a person mounted on it, the arm raised and pointing south. As the cart traveled, the statue would rotate, always pointing south regardless of which direction the chariot faced. The direction of the statue was controlled by a geared mechanism. The descriptions of the gearing in the most ancient texts are somewhat vague, but it is believed that the chariots used a configuration similar to the modern differential gearing in which an output shaft is proportional to two input shafts

In the Hellenistic world, a frequently cited early reference to proportional gearing is the odometer described by Vitruvius (1st century B.C.) and by Hero of Alexandria (1st century A.D.) and sometimes attributed to Archimedes. However, Price expressed some doubt that odometer would have functioned:

"As for the windlass and hodometer, they do, it is true, contain whole series of gears used in steps as a reduction mechanism, usually for an extraordinarily high ratio, but here the technical details are so etherial that one must doubt whether such devices were actually realized in practice. Thus Vitruvius writes of a wheel 4 feet in diameter and having 400 teeth being turned by a 1-toothed pinion on a cart axle, but it is very doubtful whether such small teeth, necessarily separated by about 3/8 inch, would have the requisite ruggedness."

Another device described by Cicero and attributed to Archimedes is a bronze planetarium. The planetarium was said to show the rise of the sun and moon around the fixed earth, the eclipses of the sun and moon at the correct time intervals, and the movements of the stars and planets. The device would have been part of the spoils brought back to Rome after the conquering of Syracuse in 212 BC. There are fewer technical details of the planetarium than there are for the odometer, however the description is particularly interesting in light of the discovery of the Antikythera Mechanism, and how near in both location and time the two devices would be.

Shifting focus to the Islamic world, the mathematician and scholar al-Biruni (ca. 975 AD) described a device he calls the Moon Box in his text An Elementary Treatise on the Art of Astronomy. The Moon Box was an astronomical calculator driven by a clockwork of eight gears. It showed the rotation of the sun and moon, phases of the moon, signs of the zodiac, days of the week and hours of the day. Price notes many distinct similarities in al-Biruni's description and the Antikythera Mechanism, down to the shape of the gear teeth, holding out the possibility that the requisite knowledge passed uninterrupted across the missing 1,000 years from the Hellenistic to the Islamic traditions.

The Astrolabe with Geared Calendar of Muhammad b. Abi Bakr (ca 1221 AD) appears to be a simplified design based on the Moon Box. Driven by clockwork, a circular window shows the phases of the moon with a number in a small square window tracking days in the lunar cycle. An additional zodiac calendar with two concentric rings shows relative positions of the sun and moon and is useful for understanding and predicting eclipses. Abi Bakr's calendar is the oldest geared mechanism which has survived in a complete state. It is part of the collection at the Museum of the History of Science in Oxford, England.

In addition to astrolabes and astronomical clocks and calendars, the Islamic literature also includes descriptions of various geared equatorium, devices used to physically model the movement of the the sun, moon and planets. All of this knowledge was transmitted to Europe in the twelfth and thirteenth centuries via the Toledo and Alfonse translations of major texts. The first significant mechanisms to appear in Europe were the equatorium of Richard of Wallingford (1292?-1336) followed shortly thereafter by the Astrarium of Giovanni Dondi dell'Orologio of Padova, built between 1348 and 1364.

Dondi's Astrarium is cited as one of the first mechanical clocks in Europe. It used a balance wheel mechanism to keep time in two second intervals. It was also a remarkably complex astronomical calculator in the tradition of the Antikythera Mechanism and Moon Box. It stood about a meter tall, and used about 107 gears and pinions to calculate and show the positions of the sun, the moon and the five known planets.

From the time of Wallingford and Dondi, the written record of clockwork development in Europe and around the world is continuous. The discovery and study of the Antikythera Mechanism completely changed our understanding of the history of clockwork, its earliest uses, and its transmission among the ancient cultures. With luck, additional artifacts or texts will emerge in the future to help fill in the vast remaining gaps in our knowledge of the development of this critical and fascinating technology.

Sources:

Marchant, Jo., Decoding the Heavens: A 2,000-Year-Old Computer--and the Century-long Search to Discover Its Secrets, Da Capo Press., Cambridge Massachusetts., 2009

de Solla Price, Derek John., On the Origin of Clockwork, Perpetual Motion Devices, and the Compass., Smithsonian Institution, United States National Museum, 1959

Needham, Joseph., Science and Civilization in China: Volume 4, Part 2. Taipei: Caves Books, Ltd., 1986

Dudley Darle W., The evolution of the gear art., American Gear Manufacturers Association., 1969

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