by Decoding the Heavens- Solving the Mystery of the World's First Computer (retail) (epub)
A pipe from the tank would have carried water at a constant rate to the measuring tank in the main part of the tower. Here, channels in the floor showed where overflow from the water tank fed three fountains. Price also found grooves that he calculated held railings to keep spectators away from the clock’s machinery. He even located some battered panels that fitted them among the heaps of marble that lay nearby. But there were some grooves that Price couldn’t interpret. He did what he usually did in such circumstances – decided that the failing was not his, but the ancient stonemason’s, who had clearly carved the marks in the wrong place by mistake.
It wasn’t possible to tell from the floor and wall markings how the time had been displayed. An hour pointer attached to the rising float or a hammer striking a gong at set times would have been in line with clocks of the period. But there was another, more spectacular alternative that Price felt would have been appropriate for the awesome Tower of the Winds.
At the turn of the century, two ancient pieces of bronze discs had been found – one in Grand, north-east France, and one by builders digging foundations for a house in Salzburg, Austria. Both were inscribed in Latin and were found with Roman remains, dated to around the second century AD. Albert Rehm studied the Salzburg fragment and published a reconstruction of it in 1903, just a few years before he first saw the Antikythera mechanism in Athens. He concluded that the complete disc must have measured more than 60 centimetres across, and that it had been the face of a large astronomical clock. The fragment was inscribed with figures representing the constellations – robed Andromeda, her naked husband Perseus with sword held high, Auriga the chariot driver, as well as the zodiac’s Pisces, Aries, Taurus and Gemini.
Rehm realised that the disc he was studying matched another type of clock that Ctesibius had designed, which provided an elegant astronomical solution to the problem of the seasons. In ancient Greek and Roman times, hours weren’t all the same length. Day (measured from sunrise to sunset) and night (sunset to sunrise) were each divided into twelve equal hours, the length of which therefore varied throughout the year. This complicated the hour markers on clocks somewhat. One way to get around this was to have different hour plates for different seasons, or even to carve curved hour lines on a cylinder that was turned a little each day.
But the Salzburg clock was basically a water-powered astrolabe. The bronze disc, marked with the constellations in the sky, was set vertically on a central axle behind a fixed set of curved wires that represented the position of the horizon and the hours of the day. The float in the water clock was connected to the axle so that as the float rose the disc turned. From the front an observer would see the stars and constellations riding clockwise through the sky, mirroring the movements of the heavens.
To account for the changing seasons, a series of holes had been punched through the disc in a circle to represent the ecliptic, the Sun’s annual path through the sky. Each hole represented the Sun’s position on a particular day. When a peg depicting the Sun was placed in the appropriate hole, the time could be read off as it sailed past the static hour lines. The ecliptic circle was offset from the centre of the disc so that in summer the peg hole would take the Sun high through the sky during the day with only a relatively short path below the horizon, the opposite being the case in winter.
Price imagined such a clock as the centrepiece of the Tower of the Winds. The gleaming bronze star disc turning inexorably and mysteriously in line with the sky must have been the main attraction of the bustling Athens marketplace. This was much more than just a timepiece. It was a spectacular celebration of the beauty of the heavens, and of man’s understanding of it. And he became convinced that although it contained no gearing, the clock was closely associated with the Antikythera fragments in scientific detail and in spirit; the notion of representing the skies with a flat disc that turned with the heavens must surely have served as an important inspiration for whoever thought up the two-dimensional dials and pointers of the Antikythera mechanism.
Another success for Derek de Solla Price! But his satisfaction didn’t last long. Arthur C. Clarke still wanted him to publish a reconstruction of the Antikythera mechanism – especially since going to see the fragments for himself. Clarke attended an astronautics congress in Athens in the summer of 1965, where American astronauts were celebrating their successful return from the Gemini 5 mission. It was the first space flight to last eight days – the length of time it would take to get to the Moon and back, and hopes were high that they would reach the Moon before the decade was out, as President Kennedy had promised. Man was no longer just observing the heavens, he was conquering it.
Clarke took time out from the party to track down the old mechanism he had heard so much about. It took reluctant museum staff several days to locate the fragments in their cigar box, and he was dismayed that such an important relic was not on display. But when he finally got to unwrap the pieces of battered clockwork, it was worth the wait. He saw immediately that what Price had been telling him was true. This was surely the most important single item to come from ancient Greece, and one of the greatest mechanical inventions of all time.
Yet coming face to face with such familiar technology was also strangely disturbing. It was the clearest possible demonstration that the Greeks were like us, with minds like ours. Where Price saw the continuing threads, Clarke also realised how much had been lost. It was unsettling to think that in the Antikythera mechanism the Greeks had come so close to our modern technology, only to fall back again for so long. He articulated his thoughts a few years later in a lecture on the limits of technology at the Smithsonian Institution in Washington DC. If the Greeks had been able to build on their knowledge, Clarke told his audience, the Industrial Revolution might have begun more than a millennium ago. ‘By this time we would not merely be pottering around on the Moon. We would have reached the nearer stars.’
5
A Heroic Reconstruction
The Moon, which is the last of the stars, and the one the most connected with the Earth, the remedy provided by nature for darkness, excels all the others in her admirable qualities.
— PLINY THE ELDER
NO MATTER WHAT story you try to tell about the twentieth century, in the end you find its course diverted by the Second World War – a great, dark smear on history that sucks in everyone and everything before releasing them, a few years later, on new trajectories. Even Price’s graphs show a blip. The supposedly inexorable growth of knowledge hangs suspended, just for a moment, before the curve begins its steady climb once more.
Some stories are only affected a little, some are pulled far off course. But every one is changed. While the Antikythera fragments are buried under Athens, so Albert Rehm endures forced retirement in Munich, Virginia Grace misses her amphoras while exiled in Cyprus, and Derek de Solla Price teaches a gruelling schedule of physics in London. All their futures depend on physicists in the United States and Germany, who are locked in a race to unleash the devastating power of the atom. The outcome will determine their subsequent paths, which will in turn lead to unforeseen collisions and crossings, opportunities that fall into place one by one, a trail of influences spreading outwards like a chain reaction and stretching into a future that will soon feel to those living it as if it could never have been otherwise.
Their trajectories are set at 5:29 a.m. on 16 July 1945, when the efforts of the 130,000 Americans working on the Manhattan Project finally come to fruition in the middle of the New Mexico desert. Twenty miles away, the physicist Richard Feynman ignores the official advice to use dark glasses, figuring that the truck windshield will protect his eyes from the radiation, and thus he becomes perhaps the only person to see the full force of the explosion. He watches the fireball turn silently from blinding white to yellow to orange before black smoke curls around its edges and grows into a cloud so dark it looks as though a hole is being ripped out of the sky. A minute and a half later, the silence is broken by a tremendous bang that steals his
breath and shakes him to the bone. The Atomic Age has begun.
Price played his part in our understanding of this era. For decades the accepted story had been that only Germany and the United States had been trying to develop nuclear weapons. US officers arriving after the war to see the dishevelled remains of Japan’s premier physics laboratory saw no reason to believe that it might once have been the site of a Japanese Manhattan Project, and the scientists they interviewed said nothing to challenge that view.
But with the help of his Japanese graduate student Eri Yagi Shizume (and still following Joseph Needham’s advice about going beyond what’s written in English), Price uncovered unpublished historical records and diary entries which showed that Japan had indeed been pursuing its own nuclear bomb in what it called Project Aeropower. Yoshio Nishina, the country’s top physicist, had been friends with Albert Einstein and Niels Bohr in Europe during the 1930s and when war broke out, the Japanese Government told him to make a nuclear bomb. He had been in the middle of building a pilot plant to concentrate the uranium-235 needed to sustain a nuclear chain reaction when the facility was bombed in an air raid in April 1945.
In 1971 Price collided once more with the fallout from that nuclear arms race, and this time it handed him a key to the Antikythera mechanism. With Arthur C. Clarke’s encouragement he had held firm to his conviction that understanding the infuriating device was of fundamental importance for everything that he had been studying. His reconstruction of it would be his biggest achievement; rewriting the history of technology, if not of our entire civilisation. But there just wasn’t enough information on the surface of the delicate fragments to see how the gears worked. Then came a breakthrough. Price saw a technical report that had been published a few months earlier by researchers at Oak Ridge National Laboratory in Tennessee. It described how gamma rays from radioactive isotopes could be used to peer inside metallic objects of artistic or archaeological importance without destroying them. His long wait was over. Now it was excitement, rather than frustration, that kept Price awake at night.
He wrote to Alvin Weinberg, the director of Oak Ridge, to ask if he could use the new imaging technique on the Antikythera fragments. Oak Ridge was one of three labs originally set up as part of the Manhattan Project, and Weinberg had played a senior role in that effort. While Robert Oppenheimer oversaw the design of the bomb at Los Alamos, New Mexico, it was Weinberg’s job in Tennessee to purify uranium-235 and work out how to produce plutonium from uranium (a process that was then carried out on a larger scale at the third site, near Richland in Washington). Back then Oak Ridge had employed a staggering 40,000 people, but it was now home to just a few thousand physicists, whose job it was to build on the knowledge gained during the war for peaceful ends, from medical imaging to nuclear power. Weinberg became a vociferous champion of the latter – so much so that when the reactor at Three Mile Island suffered a partial meltdown in 1979, he argued that it actually proved how safe the technology was, since the situation had ultimately been brought under control.
The United States wasn’t the only country keen to harness the power of the atom after the war. Having witnessed its world-changing potential, pretty much every government that could afford it set up an agency with similar aims, Greece included. So when Weinberg received Price’s letter he put him in touch with the Greek Atomic Energy Commission. The trail led to nuclear physicist Charalambos Karakalos, the head of radiography at a nuclear research lab in Athens. Price turned on his charm once more and explained what he wanted, but Karakalos was sceptical about the chances of success. His lab was still under development and was only equipped with the most elementary tools for radiography. And no one had ever tried to image anything as corroded as the Antikythera fragments – it wasn’t at all clear that there was even any structure left inside to see.
Still, the project sounded more interesting than anything else he was working on at the time, so he headed across town to the National Archaeological Museum with a small sample of radioactive thulium-170 and some radiographic film. The stable form of the element, thulium-169, has 69 protons and 100 neutrons in the nucleus of each of its atoms. But the unstable thulium-170 has one extra proton squeezed into each nucleus. One by one, its atoms undergo radioactive decay, spitting out electrons and high-energy photons (also known as gamma rays) in the process. Thulium becomes ytterbium and erbium. The number of thulium atoms left halves every 128 days, as regular as clockwork – the exact reverse pattern to the one Price had once seen traced out in books against his bedroom wall.
Karakalos set up a rudimentary darkroom and took a series of exposures of the largest piece of the mechanism. He knew that the photons emitted by the thulium would shoot through the fragment and strike the film behind it, breaking up silver bromide crystals trapped in its emulsion into ions. Any metallic atoms inside the fragment would block the photons, leaving an invisible shadow of intact molecules on the film.
Breathing softly in the dim glow of the safelight, Karakalos took the transparent, green-tinted film and delicately placed it into a bath of developing solution; this would convert the exposed silver ions into black, metallic silver atoms. And there it was. A picture that made 2,000 years pass in an instant. As the film turned black he saw jagged green shapes left behind; the outlines of precisely cut gearwheels that tumbled into view one on top of the other, rendering the sophisticated handiwork of their long-dead creator visible at last. Not that the level-headed Karakalos put it that way. ‘The images are of fair quality,’ he noted. ‘They show some new gears in fragment A.’
Karakalos went back to his lab and returned with two portable X-ray machines and a lot more film. X-rays are photons, too, kicked out of atoms when electrons are fired at an element such as tungsten. The X-rays from these machines were of lower energy than the gamma-ray source, meaning that he could use longer exposure times, and so control the amount of radiation hitting the film more precisely. Over the summer of 1972 he used them to take hundreds of images of the mechanism, painstakingly adjusting the focal distance, angle and exposure time – anything up to 20 minutes for each – to get the sharpest possible pictures of what lay inside those ragged, irregular fragments.
Price was on sabbatical in Europe that summer and he visited Athens twice to look over the radiographs with Karakalos, checking progress and studying the features of the mechanism that the images revealed. The crucial details Price needed were how the wheels were arranged – which ones meshed with which – and the number of teeth on each. This would allow him to work out the numerical ratios that were encoded by the gear trains and therefore to establish once and for all what the mechanism had been designed to calculate.
Karakalos’s wife, Emily, helped with the tooth counts – Karakalos thought she would produce the most accurate numbers as she had no preconceptions as to what numbers to expect. Every day, after laying an X-ray image on the light box in front of her, she would run her palms over its surface as if to smooth away imaginary dust, and angle a magnifying glass precisely over each wheel in turn. Closing her mind to noise and other distractions, she attended only to the tiny green zigzags, counting up the visible teeth on each and noting down the results. For the smaller wheels she used enlarged black and white prints created from the negatives, drawing a careful circle to mark the circumference of each gear and perforating each tooth tip with a pin from her sewing box. Then she’d turn the print over, to number the holes in neatest pencil on the back.
It was tedious work. All of the wheels in the mechanism appeared on top of each other in the images, up to eight layers deep, so many of the details were blotted out. Karakalos did his best to vary the exposure times and focal distance to isolate the details of each one, but even so there wasn’t a single gear for which every tooth was visible. Determining the total number of teeth, therefore, meant counting those that could be seen, measuring what angle of arc was visible, then scaling up to the entire 360° circumference. It was easy to make mistakes – the teeth on some of the wheel
s were actually quite irregular and often it wasn’t clear where the centre of a wheel was, leaving its exact size in doubt. The counts had to be repeated again and again, on print after print, until a consistent figure was established for each wheel.
Sometimes Emily became distracted, wondering at the foreign professor for whom these jumbled patterns meant so much. His enthusiasm could be infectious, but she had never seen anyone whose mood changed so quickly from one day to the next. It was especially hard to predict how he would react when he saw the results of her work. Some days he was approving and encouraging; others he would frown and demand a recount. She couldn’t understand why he could not be satisfied with the evidence from the images her husband had so carefully produced and that she had so painstakingly counted. Why look at all, if you cannot accept what you see?
When the counting was done, Price went back to Yale, shut the door to his office, and continued to work feverishly on a reconstruction of the mechanism. As well as confusing the tooth counts, the fact that all the wheels were superimposed in the images made it difficult to tell which gears meshed with which – it was hard to distinguish a gear at the front of the mechanism from one at the back, for example. He made a model to help visualise the mechanism’s workings; its two cardboard faces held on to four wooden sides with a buckled, cotton strap. He drew on the outlines of the existing fragments, then added his reconstruction of the front and back dials, complete with little cardboard pointers. Inside, he arranged and rearranged the cardboard wheels like miniature furniture.
