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Antikythera mechanism
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The Antikythera mechanism (an-ti-ki-theer-uh), is an ancient mechanical calculator (also described as the first known mechanical computer) designed to calculate astronomical positions. It was discovered in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, in 1901. Subsequent investigation, particularly in 2006, dated it to about 150–100 BC; and hypothesised that it was on board a ship that sank en route from the Greek island of Rhodes to Rome.
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The Antikythera mechanism (an-ti-ki-theer-uh), is an ancient mechanical calculator (also described as the first known mechanical computer) designed to calculate astronomical positions. It was discovered in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, in 1901. Subsequent investigation, particularly in 2006, dated it to about 150–100 BC; and hypothesised that it was on board a ship that sank en route from the Greek island of Rhodes to Rome. Technological artifacts of similar complexity did not reappear until a thousand years later.
Jacques-Yves Cousteau visited the wreck for the last time in 1978, but found no more remains of the Antikythera Mechanism. Professor Michael Edmunds of Cardiff University who led the study of the mechanism said: "This device is just extraordinary, the only thing of its kind. The design is beautiful, the astronomy is exactly right. The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely carefully." He added: "...in terms of historic and scarcity value, I have to regard this mechanism as being more valuable than the Mona Lisa."
The device is displayed in the Bronze Collection of the National Archaeological Museum of Athens, accompanied by a reconstruction made and offered to the museum by Derek de Solla Price. Other reconstructions are on display at the American Computer Museum in Bozeman, Montana and the Children's Museum of Manhattan in New York.
Origins
The mechanism is the oldest known complex scientific calculator. It contains many gears, and is sometimes called the first known analog computer, although others consider it likely that it had a number of predecessors
.
It appears to be constructed upon theories of astronomy and mathematics developed by Greek astronomers and it is estimated that it was made around 150 to 100 BC. The circumstances under which it came to be on the cargo ship are unclear. The ship is estimated to have sunk between 80 to 60 BC and was a Roman or Greek ship with cargo for Rome, perhaps part of official loot. It contained more than 100 statues similar to the ones the Romans took to Italy after their conquest of Greece. Consensus among scholars is that the mechanism itself was made in Greece. All the instructions of the mechanism are written in Greek.
One hypothesis is that the device was constructed at an academy founded by the ancient Stoic philosopher Posidonius on the Greek island of Rhodes, which at the time was known as a centre of astronomy and mechanical engineering, and that perhaps the astronomer Hipparchus was the engineer who designed it since it contains a lunar mechanism which uses Hipparchus' theory for the motion of the Moon. Investigators have suggested that the ship could have been carrying it to Rome, together with other treasure looted from the island to support a triumphal parade being staged by Julius Caesar.
However, the most recent findings of The Antikythera Mechanism Research Project, as published in the July 30, 2008, edition of Nature also suggest that the concept for the mechanism originated in the colonies of Corinth, which implies a connection with Archimedes.
Function
The device is remarkable for the level of miniaturization and for the complexity of its parts, which is comparable to that of 18th century clocks. It has over 30 gears, although Michael Wright (see below) has suggested as many as 72 gears, with teeth formed through equilateral triangles. When a date was entered via a crank (now lost), the mechanism calculated the position of the Sun, Moon, or other astronomical information such as the location of other planets. Since the purpose was to position astronomical bodies with respect to the celestial sphere, with reference to the observer's position on the surface of the earth, the device was based on the geocentric model.
The mechanism has three main dials, one on the front, and two on the back. The front dial has two concentric scales. The outer ring is marked off with the days of the 365-day Egyptian calendar, or the Sothic year, based on the Sothic cycle. Inside this, there is a second dial marked with the Greek signs of the Zodiac and divided into degrees. The calendar dial can be moved to compensate for the effect of the extra quarter day in the year (there are 365.2422 days per year) by turning the scale backwards one day every four years. Note that the Julian calendar, the first calendar of the region to contain leap years, was not introduced until about 46 BC, up to a century after the device was said to have been built (and the leap year was implemented with errors until the early first century).
The front dial probably carried at least three hands, one showing the date, and two others showing the positions of the Sun and the Moon. The Moon indicator is adjusted to show the first anomaly of the Moon's orbit. It is reasonable to suppose the Sun indicator had a similar adjustment, but any gearing for this mechanism (if it existed) has been lost. The front dial also includes a second mechanism with a spherical model of the Moon that displays the lunar phase.
There is reference in the inscriptions for the planets Mars and Venus, and it would have certainly been within the capabilities of the maker of this mechanism to include gearing to show their positions. There is some speculation that the mechanism may have had indicators for all the five planets known to the Greeks. None of the gearing for such planetary mechanisms survives, except for one gear otherwise unaccounted for.
Finally, the front dial includes a parapegma, a precursor to the modern day Almanac, which was used to mark the rising and setting of specific stars. Each star is thought to be identified by Greek characters which cross reference details inscribed on the mechanism.
The upper back dial is in the form of a spiral, with 47 divisions per turn, displaying the 235 months of the 19 year Metonic cycle. This cycle is important in fixing calendars.
The lower back dial is also in the form of a spiral, with 225 divisions showing the Saros cycle; it also has a smaller subsidiary dial which displays the 54 year "Triple Saros" or "Exeligmos" cycle. (The Saros cycle, discovered by the Chaldeans, is a period of approximately 18 years 11 days 8 hours -- the length of time between occurrences of a particular eclipse.)
The Antikythera Mechanism Research Project, with experts from Britain, Greece and the United States, detected in July 2008 the word "Olympia" on a bronze dial thought to display the 76 year Callippic cycle, as well as the names of other games in ancient Greece, and probably used to track dates of the ancient Olympic games. According to BBC news: "The four sectors of the dial are inscribed with a year number and two Panhellenic Games: the 'crown' games of Isthmia, Olympia, Nemea, and Pythia; and two lesser games: Naa (held at Dodona) and a second game which has not yet been deciphered."
Speculation about its purpose
While a century of research is finally answering the question of what the mechanism did, we are actually no nearer to answering the question of what it was for. There are numerous suggestions, any of which could be right. In order to understand the significance of this device at the period of its manufacture (c. 150 B.C.) one should be aware of the known scientific and cultural status at that period and take into account that:
- The law of universal gravitation was not discovered, so the reason for the movement of the heavenly bodies was not understood.
- The theory of planetary motion was not complete.
- The only means of transmitting knowledge were either speech or handwritten manuscripts.
However, it is not necessary to have a theory of planetary motion to compute planetary positions. The Babylonian 'System B', the mathematical formulæ which calculated planetary positions, and which the Greeks inherited, was devised by 260 BC, and perhaps as early as 500 BC.
There was a huge scientific and cultural gap between the very few educated elite who understood basic rules of solar, lunar and planetary motion and the common people who were ignorant of those things. Many ancient references from Cicero, Pliny, Plato, Seneca, Ptolemy, Aristotle et al indicate that common people viewed solar and lunar eclipses as supernatural events, linked with fear: "... easy for the ignorant to imagine that all has become confusion and doom".
Practical uses of this device have also been said to include the following:
- Astrology was commonly practiced in the ancient world. In order to create an astrological chart, the configuration of the heavens at a particular point of time is needed. It can be very difficult and time-consuming to work this out by hand, and a mechanism such as this would have made an astrologer's work much easier.
- Setting the dates of religious festivals connected with astronomical events.
- Adjusting calendars, which were based on lunar cycles as well as the solar year.
Price suggested that it might have been on public display, possibly in a museum or public hall in Rhodes. The island was known for its displays of mechanical engineering, particularly automata, which apparently were a specialty of the Rhodians. Pindar, one of the nine lyric poets of ancient Greece, said this of Rhodes in his seventh Olympic Ode:
- "The animated figures stand
- Adorning every public street
- And seem to breathe in stone, or
- Move their marble feet."
Arguments against it being on public display include:
- a) The device is rather small, indicating that the designer was aiming for compactness (it has been compared to a modern laptop computer) and, as a result, the size of the front and back dials is unsuitable for public display. A simple comparison with size of the Tower of the Winds in Athens could give us a hint to suggest that the aim of the Antikythera mechanism manufacturer was the mobility of this device rather than its public display in a fixed place (such as a university, temple, museum or public hall).
- b) The mechanism had door plates attached to it that contain at least 2,000 characters, forming what members of the Antikythera mechanism research project often refer to as an instruction manual for the mechanism. The neat attachment of this manual to the mechanism itself implies ease of transport and personal use.
- c) The existence of this "instruction manual" implies that the device was constructed by an expert scientist and mechanic in order to be used by a non-expert traveler (the text gives a lot of information associated with well known geographical locations of the Mediterranean area).
The device is unlikely to have been intended for navigation use because:
- a) Some data, such as eclipse predictions, are unnecessary for navigation.
- b) The harsh environment of the sea would corrode the gears in a short period of time, rendering it useless.
On 30 July 2008, scientists reported new findings in the journal Nature showing that the mechanism tracked the Metonic calendar, predicted solar eclipses, and calculated the timing of the Ancient Olympic Games. Inscriptions on the instrument closely match the names of the months on calendars from Illyria and Epirus in northwestern Greece and with the island of Corfu.
Similar devices in ancient literature
Cicero's De re publica, a 1st century BC philosophical dialogue, mentions two machines that some modern authors consider as some kind of planetarium or orrery, predicting the movements of the Sun, the Moon, and the five planets. They were both built by Archimedes and brought to Rome by the Roman general Marcus Claudius Marcellus after the death of Archimedes at the siege of Syracuse in 212 BC. Marcellus had a high respect for Archimedes and one of these machines was the only item he kept from the siege (the second was offered to the temple of Virtus). The device was kept as a family heirloom, and Cicero has Philus (one of the participant in a conversation that Cicero imagined had taken place in a villa belonging to Scipio Aemilianus in the year 129 BC) saying that Caius Sulpicius Gallus (consul with Marcellus' nephew in 166 BC, and credited by Pliny the Elder as the first Roman to have written a book explaining solar and lunar eclipses) gave a 'learned explanation' of it and demonstrated it working.
- When Gallus moved the globe, it happened that the Moon followed the Sun by as many turns on that bronze [contrivance] as in the Earth itself, from which also in the sky the Sun's globe became [to have] that same eclipse, and the Moon came then to that position which was [its] shadow [on] the Earth, when the Sun was in line.
So at least one of Archimedes' machines, probably (considering Gallus' interests and the fact that
that portion of the De Republica seems to be concerned with astronomical prodigia and in particular eclipses) quite similar to the Antykithera mechanism, was still operated around 150 BC.
Pappus of Alexandria stated that Archimedes had written a now lost manuscript on the construction of these devices entitled On Sphere-Making. The surviving texts from the Library of Alexandria describe many of his creations, some even containing simple blueprints. One such device is his odometer, the exact model later used by the Romans to place their mile markers (described by Vitruvius, Heron of Alexandria and in the time of Emperor Commodus). The blueprints in the text appeared functional, but attempts to build them as pictured had failed. When the gears pictured, which had square teeth, were replaced with gears of the type in the Antikythera mechanism, which were angled, the device was perfectly functional. Whether this is an example of a device created by Archimedes and described by texts lost in the burning of the Library of Alexandria, or if it is a device based on his discoveries, or if it has anything to do with him at all, is debatable.
If Cicero's account is correct (and there is reason to doubt it) then this technology existed as early as the 3rd century BC. Archimedes' device is also mentioned by later Roman era writers such as Lactantius (Divinarum Institutionum Libri VII), Claudian (In sphaeram Archimedes), and Proclus (Commentary on the first book of Euclid's Elements of Geometry) in the 4th and 5th centuries.
Cicero also says that another such device was built 'recently' by his friend Posidonius, "... each one of the revolutions of which brings about the same movement in the Sun and Moon and five wandering stars [planets] as is brought about each day and night in the heavens..."
It is unlikely that any one of these machines was the Antikythera mechanism found in the shipwreck, because both the devices fabricated by Archimedes and mentioned by Cicero were located in Rome at least 30 years later than the estimated date of the shipwreck, and the third one was almost certainly in the hands of Posidonius by that date. So we know of at least four such devices. The modern scientists who have reconstructed the Antikythera mechanism also agree that it was too sophisticated to have been a one-off device.
It is probable that the Antikythera mechanism was not unique, as shown by Cicero's references to such mechanisms. This adds support to the idea that there was an ancient Greek tradition of complex mechanical technology that was later transmitted to the Islamic world, where similarly complex mechanical devices were built by Muslim engineers and astronomers during the Middle Ages. In the early 9th century, the Banu Musa's Kitab al-Hiyal (Book of Ingenious Devices), commissioned by the Caliph of Baghdad, describes over a hundred mechanical devices, some of which may date back to ancient Greek texts preserved in monasteries. Similarly complex astronomical instruments were constructed by al-Biruni and other Muslim astronomers from the 11th century. Such knowledge could have yielded to or been integrated with European clockmaking and medieval cranes.
Investigations and reconstructions
The Antikythera mechanism is one of the world's oldest known geared devices. It has puzzled and intrigued historians of science and technology since its discovery. A number of individuals and groups have been instrumental in advancing the knowledge and understanding of the mechanism including: Derek J. de Solla Price (with Charalampos Karakalos); Allan George Bromley (with Frank Percival, Michael Wright and Bernard Gardner); Michael Wright; The Antikythera Mechanism Research Project and Dionysios Kriaris, a mathematician from Greece.
Derek J. de Solla Price
Following decades of work cleaning the device, in 1951 British science historian Derek J. de Solla Price undertook systematic investigation of the mechanism.
Price published several papers on "Clockwork before the Clock". and "On the Origin of Clockwork", before the first major publication in June 1959 on the mechanism: "An Ancient Greek Computer". This was the lead article in Scientific American and appears to have been initially published at the prompting of Arthur C. Clarke, according to the book Arthur C. Clarke's Mysterious World (see end of chapter 3). In "An Ancient Greek Computer" Price advanced the theory that the Antikythera mechanism was a device for calculating the motions of stars and planets, which would make the device the first known analog computer. Until that time, the Antikythera mechanism's function was largely unknown, though it had been correctly identified as an astronomical device, perhaps being an astrolabe.
In 1971, Price, by then the first Avalon Professor of the History of Science at Yale University, teamed up with Charalampos Karakalos, professor of nuclear physics at the Greek National Centre of Scientific Research "DEMOKRITOS". Karakalos took both gamma- and X-ray radiographs of the mechanism, which revealed critical information about the device's interior configuration.
In 1974, Price wrote "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 B.C.", where he presented a model of how the mechanism could have functioned.
Price's model, as presented in his "Gears from the Greeks", was the first theoretical attempt at reconstructing the device. According to that model, the front dial shows the annual progress of the Sun and Moon through the zodiac against the Egyptian calendar. The upper rear dial displays a four-year period and has associated dials showing the Metonic cycle of 235 synodic months, which approximately equals 19 solar years. The lower rear dial plots the cycle of a single synodic month, with a secondary dial showing the lunar year of 12 synodic months.
One of the remarkable proposals made by Price was that the mechanism employed differential gears, which enabled the mechanism to add or subtract angular velocities. The differential was used to compute the synodic lunar cycle by subtracting the effects of the Sun's movement from those of the sidereal lunar movement.
Allan George Bromley
An ingenious variant on Price's reconstruction was built by Australian computer scientist Allan George Bromley of the University of Sydney and Sydney clockmaker Frank Percival. Bromley went on to make new, more accurate X-ray images in collaboration with Michael Wright. Some of these were studied by Bromley's student, Bernard Gardner, in 1993.
Michael Wright
Michael Wright, formerly Curator of Mechanical Engineering at The London Science Museum, and now of Imperial College, London, made a completely new study of the original fragments together with Allan George Bromley. They used a technique called linear X-ray tomography which was suggested by retired consultant radiologist, Alan Partridge. For this, Wright designed and made an apparatus for linear tomography, allowing the generation of sectional 2D radiographic images.
Early results of this survey were presented in 1997, which showed that Price's reconstruction was fundamentally flawed. However, Bromley was already suffering from Hodgkin's disease and he died in 2002.
Further study of the new imagery allowed Wright to advance a number of proposals. Firstly he developed the idea, suggested by Price in "Gears from the Greeks", that the mechanism could have served as a planetarium. Wright's planetarium not only modelled the motion of the Sun and Moon, but also the Inferior Planets; Mercury and Venus, and the Superior Planets; Mars, Jupiter and Saturn.
Wright proposed that the Sun and Moon could have moved in accordance with the theories of Hipparchus, and the five known planets moved according to the simple epicyclic theory suggested by the theorem of Apollonios. In order to prove that this was possible using the level of technology apparent in the mechanism, Wright produced a working model of such a planetarium.
Wright also increased upon Price's gear count of 27 to 31 including 1 in Fragment C that was eventually identified as part of a Moon phase display. He suggested that this is a mechanism that shows the phase of the Moon by means of a rotating semi-silvered ball, realized by the differential rotation of the sidereal cycle of the Moon and the Sun's yearly cycle. This precedes previously known mechanisms of this sort by a millennium and a half.
More accurate tooth counts were also obtained, allowing a new gearing scheme to be advanced. This more accurate information allowed Wright to confirm Price's perceptive suggestion that the upper back dial displays the Metonic cycle with 235 lunar months divisions over a five-turn scale. In addition to this Wright proposed the remarkable idea that the main back dials are in the form of spirals, with the upper back dial out as a five-turn spiral containing 47 divisions in each turn. It therefore presented a visual display of the 235 months of the Metonic cycle (19 years ˜ 235 Synodic Months). Wright also observed that fragmentary inscriptions suggested that the pointer on the subsidiary dial showed a count of four cycles of the 19-year period, equal to the 76-year Callippic cycle.
Based on more tentative observations, Wright also came to the conclusion that the lower back dial counted Draconic Months and could perhaps have been used for eclipse prediction.
All these findings have been incorporated into Wright's working model, demonstrating that a single mechanism with all these functions could not only be built, but would also work.
Despite the improved imagery provided by the linear tomography Wright could not reconcile all the known gears into a single coherent mechanism, and this led him to advance the theory that the mechanism had been altered, or modified, with some astronomical functions removed, and others added.
Finally, as an outcome of his considerable research, Wright also conclusively demonstrated that Price's assumption of the existence of a differential gearing arrangement was incorrect.
Michael Wright's research on the mechanism is continuing in parallel with the efforts of the Antikythera Mechanism Research Project. Recently Wright modified slightly his model of the mechanism to incorporate the latest findings of the Antikythera Mechanism Research Project regarding the function of the pin and slot engaged gears that brilliantly simulate the anomaly in the Moon's angular velocity. On 6 March 2007 he presented his model in the National Hellenic Research Foundation in Athens.
The Antikythera Mechanism Research Project
The Antikythera mechanism is now being studied by the Antikythera Mechanism Research Project, a joint program between Cardiff University (M. Edmunds, T. Freeth), the National and Kapodistrian University of Athens (X. Moussas, Y. Bitsakis), the Aristotle University of Thessaloniki (J.H. Seiradakis), the National Archaeological Museum of Athens, X-Tek Systems UK and Hewlett-Packard USA, funded by the Leverhulme Trust and supported by the Cultural Foundation of the National Bank of Greece.
The mechanism's fragility precluded its removal from the museum, so the Hewlett-Packard research team and X-Tek Systems had to bring their devices to Greece. HP built a 3-D surface imaging device, known as the "PTM Dome," that surrounds the object under examination. X-Tek Systems developed a 12 ton 450 kV microfocus computerised tomographer especially for the Antikythera Mechanism.
It was announced in Athens on 21 October 2005 that new pieces of the Antikythera mechanism had been found. There are now 82 fragments. Most of the new pieces had been stabilized but were awaiting conservation.
On 30 May 2006, it was announced that the imaging system had enabled much more of the Greek inscription to be viewed and translated, from about 1,000 characters that were visible previously, to over 2,160 characters, representing about 95% of the extant text. The team's findings shed new light concerning the function and purpose of the Antikythera mechanism. Research is ongoing. The first results were announced at an international conference in Athens, November 30 and December 1, 2006.
New discoveries
On 30 November 2006, the science journal Nature published a new reconstruction of the mechanism by the Antikythera Mechanism Research Project, based on the high resolution X-ray tomography described above. This work doubled the amount of readable text, corrected prior transcriptions, and provided a new translation. The inscriptions led to a dating of the mechanism to around 100 BC. It is evident that they contain a manual with an astronomical, mechanical and geographical section. The name HISPANIA (?S?????, Spain in Greek) in these texts is the oldest reference to this country under this form, as opposed to Iberia.
The new discoveries confirm that the mechanism is an astronomical analog calculator or orrery used to predict the positions of heavenly bodies in the sky. This work proposes that the mechanism possessed 37 gears, of which 30 survive, and was used for prediction of the position of the Sun and the Moon. Based on the inscriptions, which mention the stationary points of the planets, the authors speculate that planetary motions may also have been indicated.
On the front face were graduations for the solar scale and the zodiac together with pointers that indicated the position of the Sun, the Moon, the lunar phase, and possibly the planetary motions.
On the back, two spiral scales (made of half-circles with two centres) with sliding pointers indicated the state of two further important astronomical cycles: the Saros cycle, the period of approximately 18 years separating the return of the Sun, Moon and Earth to the same relative positions and the more accurate exeligmos cycle of 54 years and one day (essential in eclipse prediction, see Eclipse cycle). It also contains another spiral scale for the Metonic cycle (19 years, equal to 235 lunar months) and the Callippic cycle that proposed a more accurate periodicity of 940 lunar months in approximately 76 years.
The Moon mechanism, using an ingenious train of gears, two of them linked with a slightly offset axis and pin in a slot, shows the position and phase of the Moon during the month. The velocity of the Moon varies according to the theory of Hipparchus, and to a good approximation follows Kepler's second law for the angular velocity, being faster near the perigee and slower at the apogee (see Kepler's laws of planetary motion).
On 31 July 2008, a paper providing further details about the mechanism was published in Nature (Nature Vol 454, Issue 7204, July 31, 2008). In this paper, among other revelations, it is demonstrated that the mechanism also contained a dial divided into four parts, and demonstrating a four-year cycle through four segments of one year each, which is thought to be a means of describing which of the games (such as the ancient Olympics) that took place in two and four-year cycles were to take place in any given year.
The names of the months have been read; they are the months attested for the colonies of Corinth (and therefore also traditionally assumed for Corinth and Syracuse, which have left less direct evidence). The investigators suggest that the device may well be of Syracusan design, and may descend from the work of Archimedes.
In popular culture
- Electronic musician, BT, in his 2006 album, This Binary Universe, included a track called "The Antikythera Mechanism".
- In the 2008 computer game Spore, one of the "Storybook Planets" (planets with a unique, unnatural topography) is shaped entirely of gears. The description of such a planet asks if the "Antikythera Mechanism" was invented on such a planet.
See also
External links
- Jo Marchant, New Scientist, December 12, 2008
- video of how the device works, from New Scientist on YouTube, December 12, 2008
- Jo Marchant, with
- article written in Greek and English languages by John A. Koulouris,(Esq.) for Mythopedia / IN NOMINE Portal (Athens, Greece), regarding the discovery, history, research chronology, and Antikythera Mechanism Research Project.
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