Decoding the Heavens
Page 5
Placed on top of this fixed sky map was a rotatable plate called a rete. This disc had key star constellations marked on it, as well as a circle to represent the path that the Sun follows through the sky. The whole sky rotates as the Earth turns, of course, but the Sun (because we’re going around it) appears to us to move slightly faster than the stars through the sky, gaining on them by a few degrees each day. The path the Sun traces with respect to the stars over the course of a year is called the ecliptic, because the only time you can see directly where the Sun is in relation to the background stars is during an eclipse. In ancient times, the 360-degree circle of the ecliptic was divided into twelve 30-degree sections of longitude, which correspond to the twelve signs of the zodiac. These were marked around the circumference of the astrolabe – this was the scale referred to in the sixth-century text, and in the inscription on the Antikythera mechanism.
On the rete, the spaces between the constellations were cut out so you could still see the sky map beneath (hence its name, which means ‘net’ or ‘web’). The precise positions of the stars were represented by pointers, often in the dramatic form of flames or daggers, so that as the skeletal rete was rotated over the sky map, it showed the movement of the stars through the sky. Then on top of the rete was attached a rotatable straight bar, called a rule, which represented the Sun. The Sun’s precise position on the sky map was given by the point at which the rule crossed the circle of the ecliptic. First the rule was set with respect to the ecliptic to show a particular day of the year, then it was rotated along with the rete to simulate the Sun’s movement through the heavens on that day. Extra hour lines engraved on the fixed mater beneath allowed an astronomer to use the rule to read off the time at which the Sun or any marked star would hit a particular altitude.
Astrolabes were generally used for astronomical predictions and observations (there were sights on the back for measuring the altitude of stars or the Sun). They weren’t especially helpful for navigation. Quite apart from the fact that the heavy metal disc would swing about clumsily in the wind if you tried to use it on deck, there were other, simpler devices for measuring the Sun’s noon altitude, which was all you needed to determine the latitude of a ship at sea. And astrolabes did not measure longitude – how far east or west you were. There wasn’t a way to do that until the eighteenth century, when the legendary British clockmaker John Harrison perfected clock mechanisms robust and accurate enough to be taken to sea to keep a record of the time at the ship’s home port, and therefore show the time difference between that and the hour at the ship’s present location, as indicated by the stars.
Although the first known description of an astrolabe comes from the sixth century and no actual instruments survive from before the ninth century, they were almost certainly around much earlier. The Greek astronomer Ptolemy described the maths necessary to make an astrolabe in the second century AD and reported lots of astronomical observations that were probably made using one. There’s a colourful (if unlikely) story that Ptolemy invented the instrument when he was riding on a donkey, wisely pondering his celestial globe. He dropped the globe and the donkey stepped on it, squashing it flat, and giving him the idea. There are hints in other manuscripts, however, that the astrolabe may have been invented by Hipparchus, an astronomer who lived and worked on Rhodes in the second century BC, and from whom Ptolemy took much of the astronomy that he wrote about.
Svoronos and Rediadis’s discovery of the zodiac scale certainly suggested that the Antikythera mechanism had something to do with astronomy. But it wasn’t like any other astrolabe that was known at the time. For a start, astrolabes weren’t square and they didn’t come in wooden boxes. More fundamentally, although astrolabes had scales and pointers, they didn’t have any need for gearwheels.
Like everyone else who saw the mechanism, Professor Rediadis was astonished at the sophistication of its gearing, and despite Svoronos’s relatively late dating of it to the third century AD, he struggled to believe that this wasn’t a much more recent instrument. To Rediadis, the gearing of the Antikythera mechanism looked just like the workings of a modern clock. If it wasn’t for Svoronos’s assurances that the instrument dated from centuries before the invention of the springs, regulators and escapements necessary for the continuous motion of a clockwork clock, he said, he ‘would be bent to seize the history of nautical stopwatches from [John] Harrison’.
But when it came to identifying the mechanism, Rediadis was undaunted by its lack of similarity to known astrolabes. He thought that, as in a conventional astrolabe, the ancient instrument would have used a sighting line in combination with a degree scale to measure the height of stars or the Sun in the sky. But rather than using engraved maps and scales to read off the time of the day, say, or the longitude of the Sun, he speculated that the Antikythera device was a completely new type of astrolabe that calculated these values mechanically using trains of gearwheels and showed the result by means of the pointers. Although he called it an astrolabe (a description that would ‘stick like a barnacle’, as one historian put it, for the next half-century), he was really describing a sort of clock-like mechanism that instead of running automatically after being wound, was rotated by hand and set according to the movements of the stars.
From the sparse clues offered by the Antikythera fragments it was an inspired and quite beautiful guess. Unfortunately, neither Rediadis nor Svoronos addressed the question of why anyone would bother to build such a complicated mechanism to do what an ordinary astrolabe could have done perfectly well.
In 1905 another naval historian called Konstantin Rados, who, like Rediadis, was an expert on the Battle of Salamis, published a paper arguing that the Antikythera mechanism was far too complex to have been an astrolabe. He, too, likened the gearwork to that of a clock and even thought he could see the remains of a metal spring in one of the fragments. Might this, after all, have been a mechanical clock capable of being wound? Rados could not believe that such a sophisticated device could have existed on the same ship as the ancient Greek statues recovered from Antikythera. He suggested that it must have dated from a second, much later shipwreck, and had found itself among the older remains by chance.
Two years later a young German called Albert Rehm entered the fray. He would go on to become one of the world’s greatest experts on ancient inscriptions. But at this point he had just accepted a post at the University of Munich and was still making his name. Scornful of the lack of technical detail in Rediadis’ description, and of the poor quality of his photographs, he went to Athens to examine the fragments himself, after which he sided with Rados and concluded that although it was certainly ancient, the mechanism could not possibly have been any kind of astrolabe.
By this time the fragments were being carefully, though controversially, cleaned. The treatment was revealing new markings and was necessary to prevent further corrosion of the bronze, but at the same time it destroyed some of the outer details. As a result of the cleaning, however, Rehm was able to read on the front dial of the third fragment a previously hidden and crucial word: Pachon (PACWN). Pachon is the Greek form of a month name in the ancient Egyptian calendar. There would be no use for the names of months on an astrolabe, Rehm argued, nor on any kind of navigational instrument.
He suggested that the fragments might be the remains of a planetarium. As a handle was turned, the differently sized gearwheels might have converted the motion into the appropriate speeds for each of the planets known at the time – Mercury, Venus, Mars, Jupiter and Saturn – showing their approximate paths as seen from Earth throughout the days, weeks and months of the year.
A ruffled Rediadis got his own back in 1910. In a new paper he argued that even if the mechanism wasn’t an astrolabe, then a planetarium was a much less reasonable assumption – the gearwork was much too weak and flat for such a spherical device. He repeated his somewhat dubious argument that because the object was found on a ship and it had been housed in a wooden case, it must have been one of the
ship’s instruments.
After this, work on the mechanism stalled, despite the continued bickering of some of the world’s most eminent science historians. The only major new research on the fragments around this time was done by John Theophanidis, a rear admiral in the Greek navy, who became interested in the mechanism in the 1920s when he was researching an article for a nautical encyclopaedia about the voyages of St Paul, who sailed back and forth across the Mediterranean preaching Christianity in the first century AD, before being shipwrecked on Malta while the Romans were taking him as a prisoner to Rome.
Theophanidis published his findings in 1934. As the limestone was scraped away, a large ring had been revealed on the front face of the main fragment of the mechanism, with a graded scale around its circumference. Could this be the zodiac scale referred to in the accompanying inscription? Theophanidis also confirmed that the big cross-shaped gearwheel engaged the rotation of several smaller gearwheels and he described a crank at the side that seemed to have driven the main wheel – wound by hand, Theophanidis suggested, or perhaps even driven by a water clock.
He also noted that the letters were so precise they must have been engraved not by a labourer but by a highly trained craftsman. Like all of the experts studying the device who came from a naval background Theophanidis became convinced that the mechanism was a navigational instrument. The inscriptions were instructions or rules, he concluded, which the ship’s captain would have had copied for his personal use.
Theophanidis thought, like Rehm, that the device was for calculating the precise positions of the Sun, Moon and planets, with the ratios between the gear teeth producing their appropriate speeds of movement. But he couldn’t quite give up on the astrolabe idea. In some of the engraved numbers he saw ratios reminiscent of the lines and circles of an astrolabe, and suggested that the inscriptions were instructions for tracing these markings with a ruler and compass, so that they could be used in conjunction with the instrument to solve various astronomical and nautical problems. He also speculated that by setting various pointers on the device according to the shadow cast by a nail placed in the middle of the concentric circles, it could calculate, by means of the gearing, the precise orientation of the ship.
Theophanidis became quite obsessed by the Antikythera mechanism and ended up spending many years working on his photographs of the fragments and building a model of the gearwork – to the extent that he had to sell several buildings that his family owned in the centre of Athens in order to finance his studies. But he did not publish on it again. Most of his extensive work lay unrecognised, hidden after his death within dusty piles of papers at his family home.
In the meantime, Albert Rehm’s career went from strength to strength and in 1930 he was appointed rector of the University of Munich, making him one of the most influential academics in the country. But around him, everything was changing. The Nazi party had been growing in power since the mid-1920s, aided by a severe economic depression. Rehm was horrified to see the Nazi movement gaining ground among his students and did everything he could to dissuade them, without much success. After Hitler gained power in 1933, many of Rehm’s Jewish colleagues had no choice but to flee the country. Rehm himself continued to protest vocally, earning the increasing displeasure of the regime, until he was forced to retire in 1936.
Nine years later, when the Second World War was over, Rehm was appointed rector once more in recognition of his resistance to the Nazis. But it didn’t last long. He was just as outspoken against the new authorities for not recognising the importance of classical studies in German education, and he was removed from the position again in 1946.
Such stubbornness ran through everything that Rehm worked on and, like Theophanidis, he was unable ever to give up thinking about the ancient gears of the Antikythera mechanism. After his first paper on it he studied the fragments on and off for the rest of his life, intending to solve the workings of the device beyond doubt so that he could silence his critics with one triumphant, definitive publication. But despite his achievements in other fields, the secrets of the mechanism eluded him and the final paper never came. He died from a heart attack after attending a faculty meeting against his doctor’s orders in 1949.
While Rehm had been fighting the Nazi regime, Hitler’s shadow had reached Athens too. In April 1941 German forces advanced on the city and as the king and the government fled for Crete (except for Prime Minister Alexandros Koryzis, who shot himself in despair), the National Archaeological Museum was closed down. The precious exhibits were taken from their cases and buried in boxes – some in caves in the hills around Athens, some in the underground vaults of the Bank of Greece, and the rest under the floors of the museum itself, where they were hurriedly covered with sand. There the artefacts waited out the long, dark years of occupation, hidden from the looting army. Unfortunately there was no similar way to safeguard the city’s food. The German soldiers, who had neglected to bring their own supplies, seized all they could from Athens’s warehouses. By the time the buried exhibits saw daylight again, tens of thousands of Athenians had starved to death above them.
Once the occupation was over Greece remained crippled by civil war for several years, but the museum opened again under a new director, Christos Karouzos, and between 1945 and 1964 those artefacts that had not disappeared in the confusion were gradually retrieved and put back on display. The Antikythera mechanism survived it all, but by this time the excitement surrounding it was largely forgotten. With so much disagreement over its date and identity the science historians had moved on, while to the art experts and archaeologists now working at the museum the shabby-looking fragments could not possibly compare in importance to the beautiful vases and sculptures that filled the building’s halls.
So the mysterious pieces were not put on display alongside the rest of the Antikythera haul. Once more they sat unnoticed at the bottom of a storeroom crate.
3
Treasures of War
The sight of him was made terrible by blasts of many trumpets and bugles, and by the cries and yells of the soldiery now let loose by him for plunder and slaughter, and rushing through the narrow streets with drawn swords. There was no counting of the slain, but their numbers are to this day determined only by the space that was covered with blood.
— PLUTARCH, LIFE OF SULLA
HER WOODEN STERN arched high out of the water, before swooping back on itself into a magnificent swan shape. Tucked under the hood of the stern was a tiny galley, its roof lined with terracotta tiles. Two men chatted inside as smoke from the cooking fire curled up past the swan’s neck and into the starry sky.
Around them piles of clay jars with pointed bottoms were stacked against the wall, while beneath them two huge steering oars plunged into the racing water through openings high up in the tightly planked hull. Further along the deck the dim, yellow glow from an oil lamp marked the base of a sturdy mast, which rose from the centre of the ship and supported a striking square sail. A complex system of rigging allowed the sail to be raised and lowered by a set of evenly spaced vertical ropes, like a giant Austrian blind, giving it a scalloped appearance even as it bulged forwards in the wind. At the front of the ship the bow, like the stern, curved up and away from the waves. This gave the vessel a roundly triumphant air, while a smaller mast with a second square sail completed the effect by extending jauntily forwards.
She was moving unusually low in the water. Below deck, the hold was packed to the brim. Back at port the crew had used ropes and pulleys to lift the cargo off the quay and lower it through hatches into the hold. A series of massive statues had come first, made of the finest Parian marble – giant men and horses so heavy they strained the creaking ropes to their limit. Smaller bronze and marble figures, grand furniture, armour, glassware and finally a delicate clockwork mechanism were carefully packed into the remaining spaces and lashed into place.
Then she set sail, as the blank yet ever-open eyes of her cargo stared into the darkness of the hold, he
ading for a destination that she would never reach.
It’s fair to say that up until the Second World War, scholars studying the Antikythera mechanism had floundered. They had discovered a few scattered references, including the month name ‘Pachon’ and a zodiac scale, which suggested that the device had an astronomical purpose rather than a navigational one and that it was therefore part of the cargo rather than a ship’s instrument. Otherwise, despite plenty of speculation, it was still impossible to say anything certain about the mysterious fragments, beyond the fact that they were Greek and dated from somewhere between the second century BC and the third century AD.
Scrutinising the details of the gearwheels and inscriptions, however, wasn’t the only way to investigate the mechanism. Once the wreck of the ship that carried it had been discovered, archaeologists also studied the rest of the salvaged cargo. Their discoveries help to paint a vivid picture of when the ship sailed, where her load was being taken and the sort of world from which she came. From there, we can guess at the origins of the Antikythera mechanism itself, and how it ended up on its final journey.
When the Antikythera wreck made headlines in the early 1900s, archaeology was taking its first tentative steps. Scholars knew of no other ancient ship to compare it with, so they had no way to judge very accurately who built it and when. The Archaeology Society’s 1902 report on the Antikythera finds simply notes that the timbers of the hull, which seemed to have been held together by wooden tongues snuggled tightly into slots cut in the sides of neighbouring planks, indicated ‘some curious method of boat building’.