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Antikythera Mechanism- World's earliest existing analogue computer

"Antikythera Mechanism Research Project' is jointly carried out by Cardiff University, National and Kapodistrian University of Athens, Aristotle University of Thessaloniki, National Archaeological Museum of Athens, X-Tek systems of U.K and Hewlitt Packard U.S.A."

Pritish Pradhan : August 08, 2009

The history of computing devices is taught in every school today. The origins were quite humble. The earliest counting device was the abacus. It originated in 3000 B.C. These simple machines were used in most civilizations of the ancient world with slight variations. After that the next jump in computing technologies were the 'Napier's bones' of John Napier and Charles Babbage's Analytical Engine. Advancement in gear mechanisms and clock work in the 17th century made the development of precise and compact instruments possible for the first time in history.

But the discovery of an ancient shipwreck off the coast of Antikythera island, Greece changed the face of the chronological order of the development of computers. In October 1900, Captain Dimitrious Kondos was leading a team of sponge divers near Antikythera coast. A diver Elias Stadiatos soon noticed a shipwreck 60 metres below the surface. The captain followed and returned with the bronze arm of a statue. By 1902 the Greek Education Ministry and the Hellenic Navy had joined the salvage operations. Many artifacts like a philosopher's head, a young boy, a life sized bronze statue, a Hercules etc were found.

But the archaeologist Valerious Stais made a most amazing discovery. He found a rock that had a gear wheel embedded into it. It was named the 'Antikythera Mechanism' and was originally thought of as an ancient clock. However continuous research since the past 108 years is still finding newer and more sophisticated applications of this device.

The date of the wreck and the mechanism is around 87 BC according to Yale University professor Derek de Solla Price.

The Antikythera Mecahnism's gear settings and inscriptions suggest that it was a calendar-computer. So it means that the origins were not as humble as it seems to be.  Technological devices of a similar complexity did not appear until a thousand and half years later.

All the recovered artefacts of the Antikythera wreck were taken to the National Archaeological Museum of Athens. There the 30 cm high lump of rock having a single gear wheel on its surface lay in storage for some months until one day it suddenly split apart. The curator noticed that inside the rock were the remnants of several small precision gear wheels all very tightly and compactly set. It aroused the interest of the scientific fraternity. But the piece was the first of its kind found in the world and had undergone extensive wear and tear. Also many of its original gear wheels and parts had been lost in the 2000 years it stayed under water. Hence it was not half a century later that the first tangible explanation of the use of such a device could be found. And the reproduction of the correct working model was not possible until 1997.

The function of the device was to calculate the position of the Sun, Moon and other celestial objects like possibly the five planets known at that time- Mercury, Venus, Mars, Jupiter and Saturn. It was based on the geocentric model in which the earth is taken as the centre of the universe. Later discoveries made by studying X-rays of the system reveal that it also predicted the Solar and Lunar eclipse as well as the dates of the ancient Olympic games. It also tracked the 19 year Metonic cycle, the 54 year Saros or Exeligmos Cycle and the 76 year Calliptic cycle. This was very important and must have simplified the fixing of calendars for its handlers. Alongside Olympics ancient Greece held three other 'crown' games- Pythian, Nemean and Isthmian. These games took place in a four-year cycle known as the Olympiad, which was one of the ways to measure time in that era. The Antikythera mechanism had a dial to keep track of this cycle as well.

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Construction and internal working of this device is quite advanced and precise. The level of miniaturization is the same as 18th century clocks. There are 31 gears with teeth of the shape of equilateral triangles. All the gears are enclosed inside a rectangular metallic or wooden box and were not visible outside. It has three main dials- one in the front and two at the back.

The front dial has two concentric scales. The outer ring is based on the Egyptian Sothic calendar and has markings of the 365 days of the year. The inner concentric ring has markings of the 12 Greek Zodiacs divided into degrees. A crank was used to enter the date. The front dial had at least three hands. One hand showed the date. The other two show the positions of the Sun and Moon. It might have had more hands to show the positions of the five planets but that mechanism is now lost. The Moon indicator was adjusted to show any deviation in its orbit. The inner scale of the front dial contains a small rotating ball that revolves around its axis. The ball's colour changes to black or white according to the Moon's changing phase.

There are two dials at the back- one at the top and the other at the bottom. The face of the upper dial is designed in the form of a spiral. It starts from the middle of the dial and after five turns reverses its direction turning on to the lower dial. The upper back dial is basically a calendar. It displays the 235 months of the 19-year long Metonic cycle. Each of the five turns are divided into 47 divisions each- each division represents a month. The upper dial has two subsidiary dials just like modern chronograph watches. One of them displays the 76-year long Calliptic cycle and the other displays the 4 year period of the ancient Olympiad games. There is a pointer that tracks the spiral grid like the stylus of a record player.

The lower back dial is one of the most interesting part the device. It contains the 225 divisions of the 18 years 11 days and 8 hours Saros cycle. The months where a solar or lunar eclipse would occur are marked. The Saros cycle is important because it represents the length of between the occurrence of a particular eclipse. There is a smaller subsidiary dial inside the spiral that represents the much longer 76-year long Calliptic cycle. The ancient Greeks might have got the dates of the eclipses from the Babylonian astronomer priests who had been observing the skies for centuries. The formula used was probably the Babylonian 'System B', which was inherited by the Greeks and devised in around 260 B.C.

The origins of the device are not very clear. It is agreed by researchers that it was built in Greece.  One theory is that it could be carrying the loot of the Roman General Sulla from Athens to Italy. The Greek writer Lucian states that one of Sulla's ships had sunk off the Antikythera coast at that time.

But the most obvious connection is with the greatest genius of those times- Archimedes. The calendar system used in the mechanism is quite similar to that used in the city of Syracuse located in Sicily island (It was a Greek city). Although Archimedes had died in 212 B.C, when the Romans be seized the city of Syracuse there is plenty of evidence that Archimedes used to operate devices of a similar nature. The famous mathematician Pappus of Alexandria writes that Archimedes had written a book 'On Sphere Making' (destroyed in the seize) about the construction of such devices. The surviving texts from the Library of Alexandria contain simple blueprints of some devices like the odometer (used for distance measurement).

Archimedes could not have made the Antikythera mechanism because he had died 150 years before its estimated age. But if the device is from his hometown of Syracuse then it could have followed a strong workshop tradition that goes back his time. The Antikythera mechanism was too complex a device to be one of its kinds. Many more must have existed. A lot of trial and error needs to take place before such a flawless and efficient model is produced. After the death of Archimedes the Roman general Marcus Claudius Marcellus brought two of his devices that predicted the motion of heavenly bodies. His nephew Caius Sulpicius Gallus was the first Roman to write a book on the eclipses. It was he who gave a proper demonstration of the working of Archimedes' devices. Cicero has written a first person account of their demonstration and use in his 1st century B.C book 'De re publica'. Hence it is certain that there existed a complex mechanical technology tradition at that time.

Ancient literature of that time has clear references to such devices. Cicero also writes of another device 'built recently by his friend Posidenous that tracked the movements of the Sun and the five planets just like they changed each day and night in the heavens'. Hence it was not a unique device. And it too sophisticated a device not to have any type of prototypes. But it is certainly the sole surviving type of its kind in the world. All similar devices of that time are lost today. If it had not been found then all the writings of Cicero and other scholars in this matter might have been dismissed as fiction.

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A big breakthrough came in 6 March 2007 when a working model was presented to the National Hellenic Research Foundation, Athens by Michael Wright. He was the former Curator of Mechanical Engineering of The London Science Museum and now of Imperial College, London. He used a new technique X-ray tomography with his partner Alan George Trombley. It allowed him to generate cross sectional 2-D radiographic images. He deciphered a previously unaccounted fragment, which was actually a Moon Phase display. This display is a rotating semi silvered ball on the front dial that changes colour according to the waxing or waning Moon Phase. Michael Wright also modified many assumptions of the Mechanism's first major researcher Derek J. de Solla Price owing to newer revelations from technical advances. Price had started research in 1951 and presented his working model in 1974 at Yale University.

'The Antikythera Mechanism Research Project' is jointly carried out today by Cardiff University, National and Kapodistrian University of Athens, Aristotle University of Thessaloniki, National Archaeological Museum of Athens, X-Tek systems of U.K and Hewlitt Packard U.S.A. The project is funded by the Leverhulme Thrust and supported by the Cultural Foundation of the National Bank of Greece. It has revealed 95% of the surviving inscriptions on the mechanism. HP and X-Tek systems brought their equipments to Greece. HP built a 3-D surface-imaging device that surrounds the mechanism under examination. It is known as the 'PTM Dome'. X-Tek Systems developed a 12 ton 450 kV ‘microfocus tomographer’ to reveal the interiors of the Mechanism.  Research is still continuing. The project has confirmed that the mechanism was an orrey or astronomical analogue calculator and that there were initially 37 gears out of which 30 survive. 82 fragments of the mechanism's main body have been found so far.

Advanced technical examination of the Antikythera Mechanism has revealed the extent of astronomical and mechanical engineering knowledge of the ancient civilizations of that time. The construction of such a device was possible only after using data obtained by observing the skies for centuries. Its portability and compactness suggests that it was built for easy handling. There were doorplates attached to the back and front dials. The plates had extensive inscriptions of almost 2000 characters, which was actually an instruction manual. Hence it was built for the use of non-expert users. But it was certainly not for navigation use since the gears would have got corroded within a short time and eclipse predictions are of no use to seamen. The use was perhaps to help in fixing the dates of festivals and cultural events like Olympics, to adjust the solar and lunar calendars and lessen the workload of astronomers.

In conclusion it can be said that gear mechanisms helped the world reach the Industrial Age in the 19th and 20th centuries. The working of the gear wheels of the Antikythera Mechanism is similar in use and effectiveness to modern gears. So it means that the Greeks had almost all required technology to build a steam engine at that time. Indeed the world would then have been 2000 years more advanced now. But many obstacles like constant warfare, a severe cultural and scientific gap between the few educated elite and the common populace, the tendency to keep many technological things secret must have prevented them. Also the cultural icons like libraries, temples etc of conquered cities were routinely destroyed. The populations of the defeated cities were either massacred or sold off to slavery. Even Archimedes himself died in the seize of Syracuse. The Romans had destroyed each and every brick of cities like Carthage and ploughed its ground with salt to prevent anything growing there. Considering the relative minority of the learned population of that time and the intense effort required to pursue such interests it can be said that any knowledge lost in war or tragedy was almost irreplaceable. It was because communication systems were nascent and printing technology was not there. So it was unlike modern times where all new advances immediately spread all over the world. Then knowledge was more localised and spread in institutions like temples, universities and libraries, which were the first target of attacking armies. Hence devices of a similar nature did not arrive until millennia and half later.

But all the knowledge used to build the device was not lost. The Islamic civilization inherited many of the Greek's knowledge and kept it safe while Europe rapidly slipped into the Dark Ages. Similar complex devices were built by Islamic astrologers like Al-beruni etc in the middle ages. Banu Musa's 'Kitab-al-Hiyal' of the 9th century describes a hundred mechanical devices, which were perhaps ancient Greek knowledge preserved in monasteries. It was until the Renaissance that the Europeans would rediscover this knowledge.

(Author is pursuing engineering studies in a Bhubaneswar based University)



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