Antikythera mechanism

The Antikythera mechanism (pron.: /ˌæntɨkɨˈθɪərə/ ant-i-ki-theer-ə or /ˌæntɨˈkɪθərə/ ant-i-kith-ə-rə) is an ancient analog computer^[1][2] designed to calculate astronomicalpositions. It was recovered in 1900–1901 from the Antikythera wreck,^[3] but its significance and complexity were not understood until a century later. Jacques Cousteau visited the wreck in 1978^[4] but, although he found new dating evidence, he did not find any additional remains of the Antikythera mechanism. The construction has been dated to the early 1st century BCE. Technological artifacts approaching its complexity and workmanship did not appear again until the 14th century AD, when mechanical astronomical clocksbegan to be built in Western Europe.^[5]

Professor Michael Edmunds of Cardiff University, who led a 2006 study of the mechanism, said: ^[6][7]

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 ... in terms of historic and scarcity value, I have to regard this mechanism as being more valuable than theMona Lisa.

—30 November 2006

The Antikythera mechanism is displayed at the

 National Archaeological Museum of Athens, accompanied by a reconstruction made and donated to the museum by Derek de Solla Price. Other reconstructions are on display at the American Computer Museum in Bozeman, Montana, the Children's Museum of Manhattan in New York, in Kassel, Germany, and at the Musée des Arts et Métiers in Paris.

The mechanism was housed in a wooden box approximately 340 × 180 × 90 mm in size and comprised 30 bronze gears (although more could have been lost). The largest gear, clearly visible in fragment A, was approximately 140 mm in diameter and most likely had 223 teeth. The mechanism's remains were found as 82 separate fragments of which only seven contain any gears or significant inscriptions.^[8][9]

Origins

See also: Antikythera wreck

This machine has the oldest known complex gear mechanism and is sometimes called the first known analog computer,^[10] although the quality of its manufacture suggests that it may have had a number of undiscovered predecessors^[11] during the Hellenistic Period. It appears to be constructed upon theories of astronomy and mathematics developed by Greek astronomers and is estimated to have been made around 100 BC. In 1974, British science historian and Yale University Professor Derek de Solla Price concluded from gear settings and inscriptions on the mechanism's faces that the mechanism was made about 87 BC and was lost only a few years later.^[12]

It is believed to be made of a low-tin bronze alloy (95% copper, 5% tin), but the device's advanced state of corrosion has made it impossible to perform an accurate compositional analysis.^[13]

All of the mechanism's instructions are written in Koine Greek,^{[7][not in citation given]} and the consensus among scholars is that the mechanism was made in the Greek-speaking world. One hypothesis is that the device was constructed at an academy founded by the Stoic philosopher Posidonius on the Greek island of Rhodes, which at the time was known as a center of astronomy and mechanical engineering; this hypothesis further suggests that the mechanism may have been designed by the astronomer Hipparchus, since it contains a lunar mechanism which uses Hipparchus's theory for the motion of the Moon. However, recent findings of The Antikythera Mechanism Research Project suggest that the concept for the mechanism originated in the colonies of Corinth, which might imply a connection with Archimedes.^[14]

It was discovered in a shipwreck off Point Glyphadia on the Greek island of Antikythera. The wreck had been found in October 1900 by a group of Greek sponge divers. They retrieved numerous artifacts, including bronze and marble statues, pottery, glassware, jewelry, coins, and the mechanism itself, which were transferred to the National Museum of Archaeology in Athens for storage and analysis. The mechanism itself went unnoticed for 2 years: it was a lump of corroded bronze and wood and the museum staff had many other pieces with which to busy themselves.^[15] On 17 May 1902, archaeologist Valerios Stais was examining the finds and noticed that one of the pieces of rock had a gear wheel embedded in it. Stais initially believed it was an astronomical clock, but most scholars considered the device to be prochronistic, too complex to have been constructed during the same period as the other pieces that had been discovered. Investigations into the object were soon dropped until Derek J. de Solla Price became interested in it in 1951.^[16] In 1971, both Price and a Greek nuclear physicist named Charalampos Karakalos made X-ray and gamma-ray images of the 82 fragments. Price published an extensive 70-page paper on their findings in 1974.^[15]

Coins that were found at the site by Jacques Cousteau in the 1970s date the shipwreck to shortly after 85 BC. Inscriptions on the device itself indicate that it was in use for 15 to 20 years before that. The ship carrying the device also contained vases that were in the Rhodian style. Rhodes was a trading port at that time, where the great Greek astronomer Hipparchus was thought to have worked from about 140 BC to 120 BC. After his death, an astronomy school was set up to continue his tradition and there is some speculation that this is where the mechanism originated.^[15]

It is not known how it came to be on the cargo ship, but it has been suggested that it was being taken to Rome, together with other treasure looted from the island, to support a triumphal parade being staged by Julius Caesar.^[17]

[edit]Mechanism

Schematic of the artifact's known mechanism

[edit]Operation

The mechanism was operated by turning a small hand crank (now lost) which was linked via a crown gear to the largest gear (the 4 spoked gear visible on the front of fragment A (named b1)). This allowed setting of the date on the front dial. The action of turning the hand crank would also cause all interlocked gears within the mechanism to rotate, resulting in the calculation of the position of the Sun and Moon and other astronomical information, such as moon phases, eclipse cycles, and theoretically the locations of planets.

[edit]Gearing

The mechanism is remarkable for the level of miniaturisation and the complexity of its parts, which is comparable to that of 14th-century astronomical clocks. It has at least 30 gears, althoughMichael Wright has suggested that the Greeks of this period were capable of implementing a system with many more gears. There is much debate that the mechanism may have had indicators for all five of the planets known to the ancient Greeks. No gearing for such a planetary display survives and all gears are accounted for, with the exception of one 63 toothed gear (r1) otherwise unaccounted for in fragment D.

Evans et al. suggest that to display the mean positions of the five classical planets would require only 17 further gears which could be positioned in front of the large driving gear and indicated using individual circular dials on the face. ^[18] Tony Freeth and Alexander Jones have modelled and published details of a version using several gear trains mechanically similar to the lunar anomaly system allowing for indication of the planets' positions as well as synthesis of the sun anomaly. Their system, they claim, is more authentic than Wright's model as it utilises the known skill sets of the Greeks of that period and does not add excessive complexity or internal stresses to the machine. ^[19]

The gear teeth were in the form of equilateral triangles with an average circular pitch of 1.6 mm, an average wheel thickness of 1.4 mm and an average air gap between gears of 1.2 mm. They were probably created from a blank bronze round using hand tools, this is evident because they are not all divided very evenly.^[19] Due to advances in imaging and CT technology it is now possible to know the precise number of teeth and size of the gears within the located fragments. Thus the basic operation of the device is no longer a mystery and has been accurately replicated. The major unknown now regards the presence and nature of any planet indicators.

[edit]Known gear scheme

^{[20] [21] [22]}

Gear chain diagram for the known elements of the mechanism. Hypothetical gears in italics.

The Sun gear is operated from the hand operated crank (connected to gear a1, driving the large four spoked mean sun gear, b1) and in turn drives the rest of the gear sets. The sun gear is b2 and it has 64 teeth.

The Moon train follows on from the sun train through gears b2/c1 * c2/d1 * d2/e2 then transferring through the freely rotating e3 to e5. The mechanism of e5/k1 * k2/e6 (all having 50 teeth) sits inside the ring gear e4 and on top of e3, k1 and k2 rotate with it and use it as an epicyclicplatform.

Gear e3 rotates at a velocity which equals the difference between the sidereal and anomalistic months (ratio to sun: 0.1126). e5 rotates at the ratio of the sidereal month. Both e3 and e5 rotate in the same direction. k1 is mounted on e3 so rotates at an angular velocity equal to that of e5 minus e3. k1 and k2 are not coaxial and have their axes offset by about 1.1 mm, A pin protrudes from k1 and is used to drive k2 via a slot. Because of the offset axes, k2 rotates at a varying angular velocity depending on the position of k1's pin in k2's slot (an ω/t plot would be close to sinusoidal in form). e6 is larger in diameter than e5 in order to mesh with k2. This unusual arrangement of gears is to mimic the eccentricities of the moon's orbit.

The motion then passes through to e1/b3 and through the centre of the b2 and b1 gears and the sun indicator shaft to the moon spindle. The orbit of the moon follows the rotational velocity of the moon spindle with a total ratio to the sun gear of 13.368.

The system to indicate the phases of the moon utilises further gear combinations. Gear b0 is attached to the sun indicator shaft and through the bevel gear train b0/mb3 * mb2/ma1 the phase spindle rotates at a ratio of 12.368 to the sun, imitating the synodic month.

The Metonic train is driven from the sun gear through b2/l1 * l2/m1 * m2/n1. The total ratio for this train is 0.263.

The Olympiad train follows on from the Metonic. Gears n3/o1 with a total ratio to the sun gear of 0.25.

The Callippic train follows on from the Metonic. Gears n2/p1 * p2/q1 with a total ratio to the sun gear of 0.0132.

The Saros train is driven from the sun gear following: b2/l1 * l2/m1 * m3/e3 * e4/f1 * f2/g1. The total ratio for this train is 0.222.

The Exeligmos train follows on from the Saros train. Gears g2/h1 * h2/i1 with a total ratio to the sun gear of 0.018.

[edit]Proposed planet indication schemes

Because of the large space between the mean sun gear and the front of the case and the size of and mechanical features on the mean sun gear it is very likely that the mechanism contained further gearing that has either been lost in or subsequent to the shipwreck or was removed before being loaded onto the ship. This lack of evidence and nature of the front part of the mechanism has led to numerous attempts to emulate what the Greeks of the period would have done and of course because of the lack of evidence many solutions have been put forward.

Wright proposal.

Evans et al. proposal.

Freeth et al. proposal.

Michael Wright was the first person to design and build a model with not only the known mechanism but also with his emulation of a potential planetarium system. He suggested that along with the lunar anomaly the deeper understood solar anomaly would also be indicated. He achieved this by the attachment of three meshing and equally sized gears to one of the spokes of the b1 mean sun gear. The farthest gear away from the central spindle was fitted with an offset pin over which an arm with a slot was fitted which in turn attached to the sun spindle, causing anomalous movement indicative of the solar anomaly.

The inferior planets are indicated using more gears attached to b1 or attached to a plate which is in turn attached to pillars which evidence suggests existed on b1 at one time, which are evidenced in scans of the mechanism. These gears ultimately drive disks upon which are pins onto which arms with slots are placed. The arms are attached to the relevant planet indication spindle and a combination of both the rotation of b1 and the action of the pin and slot mechanisms the planets' motions are synthesised and indicated on the front dial.

The superior planets are much more complex and their mechanisms require significant extra hardware. Each superior planet system is mounted on a separate 223 toothed main gear (this has the same tooth count as b1) which is mounted on a rectangular plate with wooden spacer blocks on each short end, these are then attached to the mechanism as a whole. The individual main gears are driven by smaller coaxial transfer gears driven by b1, as all of these gears share the same tooth counts the ratio between b1 and superior gear is 1. Each superior system is very similar with the only differences being the size of the gears. The main gears are free to rotate, the upper plate is free to rotate, the spindle gear is fixed. The main gear is driven by the b1 transfer gear and drives the smaller coaxial gear attached to its surface. This gear drives a larger transfer gear which drives two smaller gears, one of these is coaxial and on the other side of the upper plate, the other is on the same side of the upper plate and drives the pin carrier wheel which is on the other side of the upper plate. The smaller driven gear then drives the fixed gears on the top of the upper plate, the smaller of those (or in the case of the Mars mechanism the only one) drives the fixed spindle gear. Attached to the spindle is an arm with a slot which engages with the aforementioned pin carrier wheel. This whole system rotates with the mean sun gear and subtracts from that gear's angular velocity to make the required ratio and indicate it on the front face.^[23][24][25]

Evans, Carmen and Thorndike published a solution with significant differences to Wright's. Their proposal centred on what they observed as irregular spacing of the inscriptions on the front dial face which to them seemed to indicate an off centre sun indicator arrangement, this would simplify the mechanism by removing the need to simulate the solar anomaly. They also suggested that rather than accurate planetary indication (rendered impossible by the offset inscriptions) there would be simple dials for each individual planet showing information such as key events in each planet's cycle, initial and final appearances in the night sky and apparent direction changes. This system would lead to a much simplified gear system, with much reduced forces and complexity.

Their proposal used simple meshed gear trains and accounted for the previously unexplained 63 toothed gear in fragment D. They proposed two face plate layouts, one with evenly spaced dials and another with a gap in the top of the face to account for criticism regarding their not using the apparent fixtures on the b1 gear. They proposed that rather than bearings and pillars for gears and axles they simply held weather and seasonal icons to be displayed through a window.^[18]

In a paper published in late 2012 Evans et al. proposed a system of epicyclic gearing with pin and slot followers.^[26]

Freeth and Jones published their proposal in 2012 after extensive research and work they came up with a compact and feasible solution to the question of planetary indication. They also propose indicating the solar anomaly on a separate pointer to the mean sun wheel's date pointer. Their front panel display would be essentially the same as Wright's although instead of pointers with text they would use semi-precious stones for each of the indicated bodies. The materials to be used are in order from the centre outwards:

• Moon (silver)
• Mercury (turquoise)
• Venus (lapis lazuli)
• Sun (gold)
• Mars (red onyx)
• Jupiter (white crystal)
• Saturn (obsidian).

Unlike Wright's model however, this model has never been built and has only been operated as a computer simulation.

The system to synthesise the solar anomaly is very similar to that used in Wright's proposal. Three gears, one fixed in the centre of the b1 gear and attached to the sun spindle, the other fixed on one of the spokes (in their proposal the one on the bottom left) acting as an idle gear and the final positioned next to that one, the final gear is fitted with an offset pin and over said pin an arm with a slot which is in turn attached to the sun spindle inducing anomaly as the mean sun wheel turns.

The inferior planet mechanism is again similar to Wright's mechanism however it uses fewer gears. A gear is attached to the centre of b1 and meshes with another gear which uses b1 as an epicyclic platform (Venus uses the upper left spoke and Mercury the lower right). Attached to this gear is a plate to which a pin is fixed, a slotted arm goes over this pin and is attached to the indicator spindle, the spindle is rotated freely about the centre of b1 with anomaly induced by the pin and slot mechanism.

The superior planet mechanisms differ from Wright's but perform the same function using fewer gears. They all follow the same general principle of the lunar anomaly mechanism. All planet systems contain four gears: the input gear which is fixed, the pin gear, the slot gear and the output gear attached to the indicator shaft. Two mounted on offset axes using pin and slot systems and two mounted on the same axis, one driving and one being driven. All systems use ratios related to Babylonian astronomy. The superior planet gears are mounted on a sub-plate using metal bridges, which is in turn located in front of the inferior systems and attached to the wooden frame, the front dial plate is fixed on top of this.

There are in total 8 coaxial spindles of various sizes to transfer the rotation of the mechanism to the pointers. In total these additions require 18 new gears and because of the application of the sun anomaly the addition of a separate date pointer and of course the extra planet pointers giving a total of 47 gears and 8 pointers.^[27]

[edit]Fragments^[20][21][23]

Of the 82 fragments that have been found seven of the fragments are significant and contain the majority of the mechanism and inscriptions. There are also 16 smaller parts that contain fractional and incomplete inscriptions.

The seven major fragments are listed below:

Fragment	Size [mm]	Weight [g]	Gears	Inscriptions
A	180 × 150	369.1	27	Yes
B	125 × 60	99.4	1	Yes
C	120 × 110	63.8	1	Yes
D	45 × 35	15.0	1
E	60 × 35	22.1		Yes
F	90 × 80	86.2		Yes
G	125 × 110	31.7		Yes

[edit]Major fragments

Fragment A can be seen as the main fragment and contains the majority of the known mechanism. Clearly visible on the front is the large b1 gear, and under closer inspection further gears behind said gear (parts of the l, m, c and d trains are clearly visible as gears to the naked eye). The back of the fragment contains the rearmost e and k gears for synthesis of the moon anomaly, noticeable also is the pin and slot mechanism of the k train. It is noticed from detailed scans of the fragment that all gears are very closely packed and have sustained damage and displacement due to their years in the sea. The fragment is approximately 30 mm thick at its thickest point.

Fragment A also contains divisions of the upper left quarter of the Saros spiral and 14 inscriptions from said spiral. The fragment also contains inscriptions for the Exeligmos dial and visible on the back surface the remnants of the dial face itself. Finally, this fragment contains some back door inscriptions.

Fragment B contains approximately the bottom right third of the Metonic spiral and inscriptions of both the spiral and back door of the mechanism. The Metonic scale would have consisted of 235 cells of which 49 have been deciphered from fragment B either in whole or partially. The rest so far are assumed from knowledge of the Metonic cycle itself. This fragment also contains a single gear (o1) used in the Olympic train.

Fragment C contains parts of the upper right of the front dial face showing calendar and zodiac inscriptions. This fragment also contains the moon indicator dial assembly including the moon phase sphere in its housing and a single bevel gear (ma1) used in the moon phase indication system.

Fragment D contains at least one unknown gear and according to M.T.Wright possibly two. Their purpose and position has not been ascertained to any accuracy or consensus but lends to the debate for the possible planet displays on the face of the mechanism.

Fragment E was found in 1976 and contains 6 inscriptions from the upper right of the Saros spiral.

Fragment F was found in 2005 and contains 16 inscriptions from the lower right of the Saros spiral. It also contains remnants of the mechanism's wooden housing.

Fragment G is a combination of fragments taken from fragment C while cleaning.

[edit]Minor fragments

Many of the smaller fragments that have been found contain nothing of value however a few have some inscriptions on them.

Fragment 19 contains significant back door inscriptions including one reading "...76 years...." which refers to the Callippic cycle. Other inscriptions seem to describe the function of the back dials. In addition to this important minor fragment, 15 further minor fragments have remnants of inscriptions on them.

[edit]Inscriptions

Computer-generated front panel of the Freeth model.

On the front of the mechanism, there is one dial with two confirmed pointers, but, due to references on the inscriptions, there might have been as many as eight pointers. One for the day of the year and the rest representing the orbital positions for Mercury, Venus, Sun, Mars, Jupiter, Saturn and the Moon, although no fragments have been found to confirm this. It has been confirmed that the pointer for the moon also rotates on its axis to show its phase along with its position, although it is not clear whether the Sun position pointer would have been separated from a date pointer, or whether any planetary positions might have been displayed.^[14]

Since the purpose was to position astronomical bodies with respect to the celestial sphere, in reference to the observer's position on the Earth, the device was based on the geocentric model.^[28]

[edit]Front face

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 solar year by turning the scale backwards one day every four years. A 365¹⁄₄-day year was used in the Callippic cycle about 330 BC and in the Decree of Canopus in 238 BC. A few of the following months are inscribed, in Greek letters, on the outer ring:

• Mecheir
• Phamenoth
• Pharmouthi
• Pachon
• Payni
• Epeiph
• Mesore
• Epagomene
• Thoth
• Phaophi
• Hathyr
• Choiak
• Tybi

In addition, the following Zodiac signs appear on the inner ring: 'ΟN', ΧΗΛΑΙ, ΣΚΟΡΠΙΟΣ. Thus, the complete Zodiac, which is believed to be tropical as opposed to sidereal, would be:

Front panel of a 2007 reproduction.

• ΚΡIOΣ (Aries)
• ΤΑΥΡΟΣ (Taurus)
• ΔIΔΥΜΟΙ (Gemini)
• ΚΑΡΚIΝΟΣ (Cancer)
• ΛEΩΝ (Leo)
• ΠΑΡΘEΝΟN (Virgo)
• ΧΗΛΑΙ (Scorpio's Claw, i.e., Libra)
• ΣΚΟΡΠΙΟΣ (Scorpio)
• ΤΟΞΩΤΗΣ (Sagittarius)
• ΑIΓOΚΕΡΩΣ (Capricorn)
• YΔΡΟΧOΟΣ (Aquarius)
• IΧΘΕIΣ (Pisces)

Other inscriptions on the front dial are:

• {Κ} Evening
• {Λ} The Hya{des se}t in the evening
• Μ Taurus {be}gins to rise
• {N} Vega rises in the evening
• Θ {The Pleiad}es rise in the morning
• Ο The Hyades rise in the morning
• Π Gemini begins to rise
• Ρ Altair rises in the evening
• Σ Arcturus sets in the {morning}

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.

[edit]Rear face

Computer-generated back panel

In 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.^[29] 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.^[30][31]

On the back of the mechanism, there are five dials: the Metonic, the Olympiad, the Callippic, the Saros and the Exeligmos. The Metonic Dial is the main upper dial. It is a 19-year calendar with a total of 235 months. Each month is written over two or three lines within one of the 235 cells spread over a spiral with five turnings. The Corinthian months are:

1. ΦΟΙΝΙΚΑΙΟΣ (Phoinikaios)
2. ΚΡΑΝΕΙΟΣ (Kraneios)
3. ΛΑΝΟΤΡΟΠΙΟΣ (Lanotropios)
4. ΜΑΧΑΝΕΥΣ (Machaneus)
5. ΔΩΔΕΚΑΤΕΥΣ (Dodekateus)
6. ΕΥΚΛΕΙΟΣ (Eukleios)
7. ΑΡΤΕΜΙΣΙΟΣ (Artemisios)
8. ΨΥΔΡΕΥΣ (Psydreus)
9. ΓΑΜΕΙΛΙΟΣ (Gameilios)
10. ΑΓΡΙΑΝΙΟΣ (Agrianios)
11. ΠΑΝΑΜΟΣ (Panamos)
12. ΑΠΕΛΛΑΙΟΣ (Apellaios)

The Olympiad Dial is the right secondary upper dial. The dial is divided into four sectors, each of which is inscribed with a year number and the name of two Panhellenic Games: the "crown" games of Isthmia, Olympia, Nemea, and Pythia; and two lesser games: Naa (held at Dodona) and another games which has not yet been deciphered.^[32] The years on each one of the four divisions are:

1. LA (Year 1)
2. LB (Year 2)
3. LΓ (Year 3)
4. L∆ (Year 4)

The name given to each of these four division are:

1. ΙΣΘΜΙΑ, ΟΛΥΜΠΙΑ (corresponding to year 1)
2. NEMEA, NAA (corresponding to year 2)
3. ΙΣΘΜΙΑ, ΠΥΘΙΑ (corresponding to year 3)
4. ΝΕΜΕΑ, undeciphered text (corresponding to year 4)

The Callippic Dial is the left secondary upper dial, which follows a 76-year cycle, quadrupling the Methonic dial.

The Saros Dial is the main lower dial. It is an 18-year calendar with a total of 223 lunar months. Each month is represented by one of the 223 cells spread over a spiral with four turnings. This dial predicts eclipses and the predictions are shown in the relevant months as glyphs, which indicate lunar and solar eclipses and their predicted times of day. There are 51 glyphs, specifying 38 lunar and 27 solar eclipses. The glyph times are still incomplete. Beneath each glyph is an index letter. Some of the index letters are:

• Σ = ΣΕΛΗΝΗ (Moon)
• Η = ΗΛΙΟΣ (Sun)
• H\M = ΗΜΕΡΑΣ (of the day)
• ω\ρ = ωρα (hour)
• N\Y = ΝΥΚΤΟΣ (of the night)

Moreover, the divisions on the inside of the dial at the cardinal points indicate the start of a new full moon cycle.

The Exeligmos Dial is the secondary lower dial. It is a 54-year triple Saros dial. The labels on its three divisions are:

• Blank, which represents the number zero.
• H (number 8)
• Iς (number 16)

So the dial pointer indicates how many hours must be added to the glyph times of the Saros Dial in order to get the exact eclipse times.

[edit]Doors

The mechanism has a wooden casing with a front and a back door. The Back Door appears to be the "Instruction Manual". On one of its fragments, it is written "76 years, 19 years" representing the Callippic and Metonic cycles. It is also written "223" for the Saros cycle. On another one of its fragments, it is written "on the spiral subdivisions 235" for the Metonic Dial. The Front Door also has inscriptions.^[14][33]

[edit]Speculation about the mechanism's purpose

It is thought that the purpose of this device was to predict lunar and solar eclipses based on Babylonian arithmetic-progression cycles. The inscriptions on the device also support suggestions of mechanical display of planetary positions.^[34]

Derek J. de Solla Price suggested that the mechanism 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 speciality of the Rhodians. Pindar, one of the nine lyric poets of ancient Greece, said this of Rhodes:

The animated figures stand
Adorning every public street
And seem to breathe in stone, or
Move their marble feet.

—Pindar (trans. Rev. C. A. Wheelwright - 1830), Seventh Olympic Ode (95)

Arguments against the device having been on public display include the following:

1. The device is rather small, indicating that the designer was aiming for compactness and, as a result, the size of the front and back dials is unsuitable for public display. A simple comparison with the size of the Tower of the Windsin Athens would suggest that the Antikythera mechanism manufacturer designed the device for mobility rather than public display in a fixed location.
2. The mechanism had door plates that contained at least 2,000 characters, forming what members of the Antikythera mechanism research project often refer to as an instruction manual. The attachment of this manual to the mechanism itself implies ease of transport and personal use.
3. The existence of this "instruction manual" implies that the device was constructed by a scientist and mechanic for use by a non-expert traveler (the text has much information associated with well known Mediterranean geographical locations).^{[citation needed][dubious – discuss]}

The device is unlikely to have been intended for navigation use because:

1. Some data, such as eclipse predictions, are unnecessary for navigation.
2. Damp, salt-laden marine environments would quickly corrode the gears, rendering it useless.

[edit]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 known at that time. 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 great 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 participants in a conversation that Cicero imagined had taken place in a villa belonging to Scipio Aemilianus in the year 129 BC) saying that Gaius 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 both a "learned explanation" and a working demonstration of the device.

I had often heard this celestial globe or sphere mentioned on account of the great fame of Archimedes. Its appearance, however, did not seem to me particularly striking. There is another, more elegant in form, and more generally known, moulded by the same Archimedes, and deposited by the same Marcellus, in the Temple of Virtue at Rome. But as soon as Gallus had begun to explain, by his sublime science, the composition of this machine, I felt that the Sicilian geometrician must have possessed a genius superior to any thing we usually conceive to belong to our nature. Gallus assured us, that the solid and compact globe, was a very ancient invention, and that the first model of it had been presented by Thales of Miletus. That afterwards Eudoxus of Cnidus, a disciple of Plato, had traced on its surface the stars that appear in the sky, and that many years subsequent, borrowing from Eudoxus this beautiful design and representation, Aratus had illustrated them in his verses, not by any science of astronomy, but the ornament of poetic description. He added, that the figure of the sphere, which displayed the motions of the Sun and Moon, and the five planets, or wandering stars, could not be represented by the primitive solid globe. And that in this, the invention of Archimedes was admirable, because he had calculated how a single revolution should maintain unequal and diversified progressions in dissimilar motions.

When Gallus moved this globe it showed the relationship of the Moon with the Sun, and there were exactly the same number of turns on the bronze device as the number of days in the real globe of the sky. Thus it showed the same eclipse of the Sun as in the globe [of the sky], as well as showing the Moon entering the area of the Earth's shadow when the Sun is in line ... [missing text]

[i.e. It showed both solar and lunar eclipses.]^[35]

Pappus of Alexandria stated that Archimedes had written a now lost manuscript on the construction of these devices entitled On Sphere-Making.^[36][37] The surviving texts from the Library of Alexandria describe many of his creations, some even containing simple drawings. 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).^[38]The drawings 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.^[39] 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, 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 said 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..."^[40]

It is unlikely that any one of these machines was the Antikythera mechanism found in the shipwreck since 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 device was almost certainly in the hands of Posidonius by that date. The scientists who have reconstructed the Antikythera mechanism also agree that it was too sophisticated to have been a unique device.

This evidence that the Antikythera mechanism was not unique adds support to the idea that there was an ancient Greek tradition of complex mechanical technology that was later, at least in part, transmitted to the Byzantine andIslamic worlds, where mechanical devices which were complex, albeit simpler than the Antikythera mechanism, were built during the Middle Ages.^[41] Fragments of a geared calendar attached to a sundial, from the 5th or 6th centuryByzantine Empire, have been found; the calendar may have been used to assist in telling time.^[42] In the Islamic world, Banū Mūsā's Kitab al-Hiyal, or Book of Ingenious Devices, was commissioned by the Caliph of Baghdad in the early 9th century AD. This text described over a hundred mechanical devices, some of which may date back to ancient Greek texts preserved in monasteries. A geared calendar similar to the Byzantine device was described by the scientistal-Biruni around 1000, and a surviving 13th-century astrolabe also contains a similar clockwork device.^[42] It is possible that this medieval technology may have been transmitted to Europe and contributed to the development of mechanical clocks there.^[5]

[edit]Investigations and reconstructions

Reconstruction of the Antikythera mechanism in theNational Archaeological Museum, Athens (made by Robert J. Deroski, based on Derek J. de Solla Price model)

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: pioneering German Philologist Albert Rehm; Derek J. de Solla Price (with Charalampos Karakalos and his wife Emily); Allan George Bromley (with Frank Percival, Michael Wright and Bernard Gardner); Michael Wright and The Antikythera Mechanism Research Project.

[edit]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".^[43][44] and "On the Origin of Clockwork",^[45] before the first major publication in June 1959 on the mechanism: "An Ancient Greek Computer".^[46] 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 published "Gears from the Greeks: the Antikythera mechanism – a calendar computer from ca. 80 BC",^[47] 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 based on its inner structure revealed by the radiographs. 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.

[edit]Allan George Bromley

Professor Allan Bromley, a computer scientist of the University of Sydney improved on Price's reconstruction with the help of Frank Percival, a clockmaker. Having tested Price's theory using Meccanoparts, he found that the mechanism was unworkable. Working with Percival, he improved the device by altering the function of the handle so that one complete rotation would correspond to a single day, which he considered to be the most obvious astronomical unit. Bromley worked with the same set of parts as Price, but suspected that a gap in the mechanism was originally home to several extra gears.^[48]

Another breakthrough by Bromley concerned a train of gearing which appeared to have 15 and 63 teeth, for which Price had been unable to discover a purpose. Price considered these numbers to be too difficult to work with, and assumed that they should be corrected to 16 and 64, theorising that it could have operated a four-year cycle on the device. Bromley worked with the original count of 15 and 63 teeth, discovering that the train's cycle was four and a half years; four of such cycles equalled 18 years, a duration equal to the cycle of eclipses. With this gearing, the mechanism worked correctly, with the pointer moving into a new square for each new moon, as the handle is turned, meaning that each square on a dial represented one month. Over 223 months, or 18 years, the complete cycle is shown.^[48]

Bromley went on to make new, more accurate X-ray images in collaboration with Michael Wright.

[edit]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 2Dradiographic images.^[49] Early results of this survey were presented in 1997, which showed that Price's reconstruction was fundamentally flawed.^[50]

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).^[51][52]

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 Apollonius. 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.^[53][54]

Wright also increased upon Price's gear count of 27 to 31^[52] including 1 in Fragment C that was eventually identified as part of a Moon phase display.^[55] 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,^[56] allowing a new gearing scheme to be advanced.^[57] 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.^[58]

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.^[59]

All these findings have been incorporated into Wright's working model,^[58] demonstrating that a single mechanism with all these functions could be built, and would 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, with some astronomical functions removed and others added.^[58]

Finally, as an outcome of his considerable research,^{[49][58][60][61][62][63][64]} Wright also conclusively demonstrated that Price's suggestion of the existence of a differential gearing arrangement was incorrect.^[55][58]

In 2006 Wright completed what he believed to be an almost exact replica of the mechanism.^[65]

Michael Wright's research on the mechanism is continuing in parallel with the efforts of the Antikythera Mechanism Research Project (AMRP). Recently Wright slightly modified his model of the mechanism to incorporate the latest findings of the AMRP regarding the function of the pin and slot engaged gears that 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.

[edit]The Antikythera Mechanism Research Project

The Antikythera mechanism is now being studied by the Antikythera Mechanism Research Project,^[66] 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^[67] and Hewlett-Packard USA, funded by the Leverhulme Trust and supported by the Cultural Foundation of the National Bank of Greece.^[68]

The mechanism's fragility precluded its removal from the museum, so the Hewlett-Packard research team^[69] 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 in 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.

In May 2006, it was announced that the imaging system had allowed 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 on the function and purpose of the Antikythera mechanism. The first results were announced at an international conference in Athens in November and December 2006.^[66]

[edit]Nature papers

[edit]2006

In 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.^[70] 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 150 to 100 BC. It is evident that they contain a manual with an astronomical, mechanical and geographical section.

The new discoveries confirm that the mechanism is an astronomical analog calculator or orrery used to predict the positions of celestial bodies. 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 centers) 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 with a period of 1016 lunar orbits 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 appears to vary 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.

Access to the full text of this 2006 paper requires a paid subscription. However, the submitted version and supplementary data can be read on-line.^[71]

[edit]2008

In July 2008, a paper providing further details about the mechanism was published in Nature.^[14] In this paper it is demonstrated that the mechanism also contained a dial divided into four parts, and demonstrated 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, Kerkyra, Epidamnos, and Syracuse, which have left less direct evidence). The investigators suggest that the device might well be of Syracusan design and so descend from the work of Archimedes; alternatively it could have been ordered by and customized for any of these markets and was being shipped.

Access to the full text of this 2008 paper requires a paid subscription. However, the submitted version can be downloaded.^[72]

[edit]2010

Nature published another study in November 2010, ^[73] which suggests that the mechanism may be based on computation methods used in Babylonian astronomy, not ancient Greek astronomy, implying that Babylonian astronomy inspired the Greek counterpart; including the mechanical constructs.

The article concentrates on suggestions by James Evans, Christián Carman and Alan Thorndike that a simpler gearing system was used to display key events of displayed bodies. Their first suggestion is that the zodiac indicator dial was unevenly graduated to comply with the sun's anomalous progress through the sky. This system would simplify the sun's gear system. However the uneven graduation of the zodiac dial would lead to any planet indicators not being very accurate. To overcome this problem they suggest that each planet had a dial of its own and rather than showing precise location indication they simply show key events in each planet's cycle, such as initial and final appearances in the night sky and direction changes. This would supply the same information as a complex epicyclic gearing system but using much simpler gear trains.

The article also states that inscriptions are still being deciphered from x-ray images.

[edit]Tony Freeth and Alexander Jones's additions

In their 2012 article for the Institute for the Study of the Ancient World (ISAW) entitled The Cosmos in the Antikythera Mechanism they suggest that it is quite likely that the mechanism included gearing and indicators for the planets as well as possibly indicating solar anomalies.^{[citation needed]}

They base their proposal on inscriptions detailing the motion of the five known planets as well as on the noticeable holes and brackets on the main driving gear.

They suggest that the mean sun wheel (b1) may have been utilised as a carrier for various gear trains and other hardware and they describe and simulate how this could have been possible. They also describe in detail the evidence they have found for additional fixings on the gear. These include bearings for shafts on some of the spokes, a recess and a raised flat area possibly used to attach fixings with solder or rivets and pillars around the edge of the wheel which were potentially used to hold a sub plate and fixing bridges. They also find evidence for a 1 mm hole drilled lengthwise into the spoke at the bottom left; this would have been a complex technical achievement at the time and they are unable to explain its purpose, but tentatively suggest something to do with lubrication.

Their model simulates the solar anomaly, inferior planets and superior planets and indicates their positions on the front face along with the date and lunar pointers.

Investigations reveal that their simulated mechanism is not particularly accurate, the Mars pointer being up to 38° out at times. This is due to the inaccuracies of the Greek theories of the planets and the lack of detailed knowledge by the same.

In short, the Antikythera Mechanism was a machine designed to predict celestial phenomena according to the sophisticated astronomical theories current in its day, the sole witness to a lost history of brilliant engineering, a conception of pure genius, one of the great wonders of the ancient world—but it didn’t really work very well!

—The Cosmos in the Antikythera Mechanism , 2012  

The Antikythera mechanism (Fragment A - front)