by Decoding the Heavens- Solving the Mystery of the World's First Computer (retail) (epub)
Claudian, writing in Rome in 400 AD, was more poetic: ‘An old man of Syracuse has imitated on Earth the laws of the heavens, the order of nature, and the ordinances of the gods. Some hidden influence within the sphere directs the various courses of the stars and actuates the lifelike mass with definite motions. A false zodiac runs through a year of its own, and a toy moon waxes and wanes month by month. Now bold invention rejoices to make its own heaven revolve and sets the stars in motion by human wit.’
The device must have been highly prized, because the Roman general Marcellus took it home with him in 212 BC when his army sacked Syracuse, killing Archimedes in the process (supposedly as he was in the middle of a mathematical proof). The globe was the only thing Marcellus claimed for himself from the huge booty that was captured, and it was kept in his family in Rome for generations, until Cicero saw it years later. He wrote that Archimedes must have been ‘endowed with greater genius than one would imagine it possible for a human being to possess’ to have built such an unprecedented machine. Cicero was a big fan of Archimedes; while serving as Rome’s representive in western Sicily in 75 BC he had sought out the mathematician’s grave, which he found covered in brambles and thorns, and cleaned it up as a mark of respect.
Again, historians have never known quite what to make of such descriptions, none of which include any technical details about how the device was made. But the Antikythera mechanism helps us to take the story seriously. The way that Cicero talks about Archimedes (‘endowed with greater genius than one would imagine it possible’) suggests that he was the first to build such a contraption. Whoever was behind the Antikythera mechanism itself, the tradition may well have started generations earlier, with Archimedes.
The theory of epicycles was very new when Archimedes lived, if it existed at all, and there was certainly no way to model the elliptical orbits of the Moon and Sun. So his device might have been relatively simple, perhaps a schematic model showing the Sun, Moon and planets rotating around the Earth at various but constant speeds. Cicero simply said that Archimedes ‘made one revolution of the sphere control several movements utterly unlike in slowness and speed’, so it’s possible that this was the case. Later, other engineers could have built on the tradition, coming up with more sophisticated gearwork to incorporate the latest astronomical knowledge – including that of Hipparchus – as it became available. Perhaps Hipparchus or his work influenced a switch on Rhodes from a schematic model to a mathematical calculator that displayed the precise timing of celestial positions and events on its dials.
It’s impossible to know for sure, of course. But we know that Archimedes pioneered the use of gears in simple weight-lifting devices, using single pairs of differently sized wheels to change the force applied to an object. Maybe he also had the idea of using more precise clockwork to control the speed of spinning model planets. One of the few biographical details that slipped into his treatises was that his father Phidias was an astronomer, so it makes sense that Archimedes would have been interested in the heavens. We also know that he worked with Ctesibius in Alexandria before he moved to Syracuse, so perhaps the seeds of both modelling traditions – of planets and of living creatures – were sown with the pair of them there. Intriguingly, the mathematician Pappus, working in Alexandria in the fourth century AD, said that Archimedes wrote a treatise called ‘on sphere-making’, apparently his only work on ‘practical matters’. No copy of this document survives, but it’s not a huge stretch to imagine that it explained how to build devices that model the movements of celestial bodies around the Earth.
More recent studies of the Antikythera mechanism suggest an even stronger link with Archimedes. After Tony Freeth’s Nature paper was published in 2006 he called in Alexander Jones, a historian of astronomy from the Institute for the Study of the Ancient World in New York. Jones worked with Yanis Bitsakis and Tony Freeth to make a closer study of the Greek inscriptions that had been revealed in X-Tek’s CT images and in particular the letters covering the five-ring spiral dial on the upper part of the instrument’s back face. Michael Wright had originally shown that this spiral was divided into 235 sections, depicting the 235 synodic months of the 19-year Metonic cycle, which tracks the motions of the Sun and the Moon.
The results, published in Nature in July 2008, were completely unexpected. One surprise came from the subsidiary dial located inside the main spiral. The gear train leading to it is lost, but because it was divided into four both Michael Wright and Tony Freeth had assumed that it represented the Callippic 76-year cycle – four times the 19-year cycle displayed on the main spiral. But when Jones read the names inscribed on this dial he realised that it was doing something quite different. The inscriptions – Isthmia, Olympia, Nemea and Pythia – referred to the Panhellenic games, at which athletes from across the Greek world gathered to compete in events such as running, long jump, discus and wrestling.
Knowing which games were held when was of no astronomical use, but it had huge cultural significance. The Greeks often kept track of time by using the Olympiad 4-year cycle, so this dial would have enabled the user of the Antikythera mechanism to convert the date shown on the front dial into the Olympiad calendar. The presence of this dial supports the idea that the mechanism was not an astronomer’s tool but was meant for popular demonstrations, albeit to relatively small groups of educated intellectuals (the mechanism would have been too small to display to a large crowd).
Alexander Jones was also able to read the month names inscribed on the surviving sections of the main spiral, and he found that they too came from a local civic calendar. The inscriptions showed which months should have 29 days instead of 30, as well as which years should have 13 months instead of 12, so that the calendar fitted neatly into the 19-year astronomical cycle also shown on the dial. The calendar follows rules similar to those described by the astronomer Geminus, who worked on Rhodes in the first century BC, and the spiral was arranged so that the 29-day months all lined up along the same spokes.
The discovery of this civic calendar raised an exciting possibility. In ancient Greece, different cities used different sequences of months in their calendars, so it was now possible to investigate where the month names on the Antikythera mechanism came from. Jones did indeed find a match – and it turned upside down everyone’s ideas about where the mechanism was made. The month names inscribed on the device do not come from Rhodes. Instead, they were used in colonies founded by the city state of Corinth in central Greece. Not much is known about the calendar used in Corinth itself, but the month names used on the Antikythera mechanism are similar to those used in Illyria and Epirus in northwestern Greece, and in Corfu – all of them Corinthian colonies. Corinth had another important colony, however: Syracuse, where Archimedes lived. We don’t have any direct evidence of the calendar used in Syracuse, but the closest match of all to the month names on the Antikythera mechanism is with the calendar of Tauromenion in Sicily, which is thought to have been founded by settlers from Syracuse. Seven of the months on the mechanism are identical in name and sequence to those used in Tauromenion, and it seems likely that the original settlers took these directly from the calendar of their home state Syracuse.
Corinth and Epirus were destroyed by the Romans in the second century BC, so it’s unlikely that the Antikythera mechanism – made several decades later – was created for use there. But Syracuse, despite having been sacked by Marcellus in 212 BC, was still Greek-speaking in the first century BC and relatively prosperous. The Romans exacted heavy taxes, but as in Rhodes, the city’s citizens were reasonably free to get on with their lives. So, this new evidence suggests that although the Antikythera mechanism almost certainly began its final voyage in the eastern Mediterranean, it was originally made by (or for) someone in Syracuse in the west.
The Antikythera ship did not stop at Sicily – it sank when it was still far to the east of that island. But it was headed in that direction; its likely route to Rome would have taken it straight past Syracuse. Perhap
s the wealthy owner of the Antikythera mechanism had visited Posidonius’ school in Rhodes to show off his latest toy to the philosophers there, then boarded the ill-fated vessel on his way home. Or perhaps the mechanism was made to order by one of Rhodes’ finest craftsmen and was being delivered to a buyer in Syracuse. However, the dating of around 100 BC suggests that the instrument was probably several decades old when the Antikythera ship sailed in 70–60 BC. So its owner could have moved from Syracuse to Rhodes or elsewhere in the eastern Mediterranean and taken the mechanism with him. Or perhaps it was taken east as a prized gift or religious offering. Later the device ended up being carried west again, as booty for Rome.
Whatever the Antikythera mechanism’s story, it seems likely from all the evidence, including Cicero’s writings, that similar geared models were being made at this time in both Syracuse and Rhodes. The mechanical tradition begun by Archimedes in Syracuse a century earlier was still going strong, with his original design being updated by the latest astronomical knowledge from Rhodes and elsewhere as it became available. The latest models were then shipped across the Greek-speaking world.
In fact, a wide tradition of such devices seems to have continued until at least the fourth century AD. The mathematician Pappus, who lived in Alexandria then, wrote that in his time there was a whole class of mechanics called sphere-makers who ‘construct models of the heavens’. These models may never have got any more sophisticated than the Antikythera mechanism, however. Developing complex technology takes a thriving urban environment with stability, money, skilled craftsmen and rich clients. All those could be found in the Hellenistic world, but it wasn’t to last for long. By the beginning of the first century BC, Syracuse and Rhodes were two of the last places that Greek scholars could work uninterrupted. But Syracuse gradually declined under the influence of the Romans and Rhodes too was sacked by the Roman general Cassius in 43 BC, and never regained its former greatness.
Although they appreciated Greek science and philosophy as much as Greek art, the Romans never practised much science themselves, and there was a gradual decline in scientific learning throughout the period of the Roman empire. From the third century AD onwards the few scientists that were around did little original work; instead, they just tended to write commentaries on the works of their Hellenistic predecessors (Pappus was one of the last great Greek mathematicians). And when the Roman empire fell, the light of scholarship in Europe went out almost completely. It took nearly a thousand years for western society to recover.
We now know, of course, that Price was right when he argued that the technology incorporated in the Antikythera mechanism wasn’t totally lost. The sixth-century geared sundial that was brought in pieces to Judith Field and Michael Wright at the Science Museum proved to be a vital piece of evidence, showing that at least a simplified form of the technology survived into the Byzantine Empire. (So did the tradition of automated figures. In the tenth century, Emperor Constantine VII was still religiously following the principle of inspiring wonder in the masses – Bishop Liutprand of Cremona wrote after visiting him that his throne, which could be raised and lowered at will, was surrounded by mechanical beasts, including roaring lions and a tree with singing birds.)
During the seventh and eighth centuries the Arabs conquered large regions, including Syria, Iraq, Egypt, Mesopotamia, Iran and Spain. The rulers converted their new subjects to Islam and saw it as their duty to make the old Greek knowledge available in Arabic. During the ninth century they funded efforts to translate all the Greek texts that could be found, even going on missions into Byzantine territory to rescue them. Price knew of two examples of Islamic geared calendars – the ‘Box for the Moon’ described by al-Biruni in Ghazna (now in Afghanistan) in the eleventh century, and one attached to a surviving astrolabe made in Isfahan (now in Iran) in the thirteenth century.
Another example has turned up recently – the Box for the Moon is also described in a tenth-century treatise that appeared for sale in 2005, attached to a sundial and with a layout exactly like the one that Michael Wright reconstructed for the Byzantine instrument. The treatise isn’t signed, but is thought to have been written by an astronomer called Nastulus, who worked in Baghdad around 900. The fact that this version of the geared calendar is attached to a sundial, as in Wright’s instrument, makes the link between the Byzantine and Islamic instruments even more certain, and together all of the examples suggest that the idea of using gears to model the motions of the Sun and Moon was common in the Islamic world and inherited directly from the Greeks.
Islamic engineers also built on the Greek tradition of water clocks and they described impressive timepieces driven by both water and mercury, including one called the ‘clock of Archimedes’. Some of them had rotating dials to represent the sky, just as Derek de Solla Price described for the Tower of the Winds, as well as moving figures and audible chimes, such as balls dropping on to cymbals. Most had very simple gearing, however. They were limited because in general running water isn’t powerful enough to drive large numbers of wheels (for this reason the Antikythera mechanism was almost certainly turned by hand).
But there’s one exception that supports Price’s idea that Greek gearing techniques used in the Antikythera mechanism directly influenced the development of clocks. It’s an Arabic manuscript, only discovered in the 1970s, but written in the tenth or eleventh century in Andalusia by an engineer called Al-Muradi. In it he describes a number of water clocks. The manuscript is badly defaced, but it’s just possible to get an idea of how they work. Most water clocks we know about from the Islamic world are quite delicate devices, but Al-Muradi’s are large and rugged – driven by fast-moving streams and involving huge wheels, ropes and hefty weights. The gearing gets quite complex, including what look like epicyclic gears. Al-Muradi said he was writing to revive a subject in danger of being forgotten, suggesting that rather than being a new invention the technology had been around for some time. So it’s possible that epicyclic gearing, too, made it through from the Greeks.
Meanwhile, the wheel of history kept turning. Europe had been gathering its strength and in a series of Crusades spanning the twelfth and thirteenth centuries much territory was won back from the Muslims, including Spain. Again, the new rulers wanted to make the old knowledge available to the Christian world, and they funded a systematic effort to translate old documents into Latin – both Arabic versions and the Greek originals.
By this time the Catholic church was keenly interested in finding a means for accurate timekeeping to control the work and prayers of its monks. It had been using marked candles for centuries, but as soon as Islamic knowledge started to make it into Christian Europe water clocks appeared in monasteries there. In 1198, during a fire at the abbey of Bury St Edmunds, the monks ‘ran to the clock’ to fetch water. And an illustration in a manuscript dated to around 1285 shows a water clock in a monastery in northern France, with a wheel that rang bells as it turned.
Around this time, some unknown genius finally invented the one component that was still needed to make the switch to fully mechanical clocks: the escapement. It was particularly important for the monasteries to have clocks that rang bells (to make sure that the monks woke up for prayers during the night). Perhaps someone was experimenting with getting oscillating weights or hammers to strike bells as an alarm mechanism. Instead of being driven by the clock, they realised that the oscillating motion allowed the weights to regulate the power needed to drive it.
Once clocks were mechanically driven they were powerful enough to incorporate many more gearwheels and they exploded in complexity. Within a few decades clocks appeared all over Europe and almost immediately they incorporated elaborate astronomical displays with dials and pointers that were spookily similar to their ancient predecessors, such as the Antikythera mechanism and the Tower of the Winds. The clock of Richard of Wallingford, completed in St Albans in 1336, is one of the first that we know of. It had a large astrolabe-style dial that showed the position of the Sun
in the zodiac, the Moon’s age, phase and node, a star map and possibly the planets. (Modern additions included a Wheel of Fortune and an indicator of the state of the tide at London Bridge.) Giovanni de’ Dondi completed his clock in Padua, Italy, in 1364. As the reconstruction in the Science Museum still shows, this seven-sided construction had dials showing the time of day, the motions of all the known planets, a calendar of fixed and moveable feasts, and an eclipse prediction hand that rotated once every 18 years according to the Saros cycle.
The speed with which these astronomical displays became so elaborate and so widespread – and their similarity to those developed by the Greeks – suggests that all this did not emerge from scratch. Various pieces of the necessary technology, and the idea of using gearwheels to simulate the heavens, must have been lying dormant in a range of devices – including water clocks and hand-driven calendars – so that when the invention of the escapement allowed the construction of a mechanical clock, all of these old tricks came rushing out of the wings into the new tradition.
Once again, geared astronomical displays were used to demonstrate the wonder of the heavens – and to solidify the position of the church – and they were placed prominently in big clock towers and public squares. They often included mechanical figures, too, clearly influenced by Greek automata. The St Mark’s clock in Venice, completed in around 1500, which used seven concentric dials to display the time and the movements of the Sun and Moon in the zodiac, was topped by two bronze giants that struck an enormous bell, as well as moving statues of Mary, Jesus and the Three Kings. And the Strasbourg clock, completed around 1350, included a bronze cock that flapped its wings at midday and crowed three times through a small organ in its throat.