Wednesday, August 10, 2011

Ancient Culture and Technology: the near misses of ancient times

People tend to think of history as linear, progressing towards ever more complex and sophisticated societies. Any study of Roman, Chinese or other complex culture will show that ups and downs are common. More importantly, technology is not linear. Concrete was invented by ancient Rome (possibly by Egypt, though I think the jury is still out on that) then forgotten until 1756, when a British engineer, John Smeaton invented modern concrete (which only got its name around 1830).

But there are even more mysterious examples of amazing technology that seemed to go nowhere despite being what we would consider far ahead of its time. Sometime around between 1900 BCE and 1600 BCE, long before the Chinese invented movable type, something not so different was invented on the Minoan Island of Crete.

The Phaistos Disc is a unique find that may never be figured out, but it was clearly made using stamps to impress symbols (possibly syllabic writing) in the clay of a disc. No other comparable object, use of stamped impressions to simplify complex writing, or examples of this writing has ever been found. It stands out as ahead of its time and completely baffling. SOMEONE made it. SOMEONE made the stamps used to make the impressions. SOMEONE knew what the symbols meant. We may never know what that someone knew. I have always been fascinated by the Phaistos disc, both because I have always been fascinated with Minoan culture, but also because it is so unlike anything of its time or of any time for a long time after.

And then there was the steam engine invented by Hero of Alexandria in around 50 CE. However, though not a bad idea, there is no evidence that Hero's design was ever tried out and there is some question whether Hellenistic metalurgy could produce a tight enough mechanism to maintain the steam pressure needed for it to work. Had it worked, the industrial revolution just might have occurred by 100 CE.

But that is nothing compared with another discovery from Greece that actually worked.

The Antikythera Mechanism is perhaps the most amazing item ever discovered from ancient times, and it has been well enough preserved that we can probably reconstruct the entire mechanism and see how it works. Dating from sometime around 100 BCE, this device was preserved in a shipwreck for 2000 years before being discovered in 1902. Filled with gears, the device looks extremely similar to a wind-up wrist watch!

People have devoted their lives to trying to figure out what this thing does. And, as reported in the November 30, 2006 issue of Nature, they have probably figured it out as well as making a working model. From the News Feature about of the article:

The mechanism is contained in a squarish wooden case a little smaller than a shoebox. On the front are two metal dials (brass, although the original was bronze), one inside the other, showing the zodiac and the days of the year. Metal pointers show the positions of the Sun, the Moon and five planets visible to the naked eye. I turn the wooden knob on the side of the box and time passes before my eyes: the Moon makes a full revolution as the Sun inches just a twelfth of the way around the dial. Through a window near the centre of the dial peeks a ball painted half black and half white, spinning to show the Moon's changing phase.

On the back of the box are two spiral dials, one above the other. A pointer at the centre of each traces its way slowly around the spiral groove like a record stylus. The top dial, Wright explains, shows the Metonic cycle — 235 months fitting quite precisely into 19 years. The lower spiral, according to the research by Edmunds and his colleagues, was divided into 223, reflecting the 223-month period of the Saros cycle, which is used to predict eclipses.

To show me what happens inside, Wright opens the case and starts pulling out the wheels. There are 30 known gear-wheels in the Antikythera Mechanism, the biggest taking up nearly the entire width of the box, the smallest less than a centimetre across. They all have triangular teeth, anything from 15 to 223 of them, and each would have been hand cut from a single sheet of bronze. Turning the side knob engages the big gear-wheel, which goes around once for every year, carrying the date hand. The other gears drive the Moon, Sun and planets and the pointers on the Metonic and Saros spirals.

And they can take a stab at either the inventor of the device, or, more likely, the person who inspired the inventor:

One of the wheels connected to the main drive wheel moves around once every nine years. Fixed on to it is a pair of small wheels, one of which sits almost — but not exactly — on top of the other. The bottom wheel has a pin sticking up from it, which engages with a slot in the wheel above. As the bottom wheel turns, this pin pushes the top wheel round. But because the two wheels aren't centred in the same place, the pin moves back and forth within the upper slot. As a result, the movement of the upper wheel speeds up and slows down, depending on whether the pin is a little farther in towards the centre or a little farther out towards the tips of the teeth (see illustration on page 551).

The researchers realized that the ratios of the gear-wheels involved produce a motion that closely mimics the varying motion of the Moon around Earth, as described by Hipparchus.

Unlike the Phaistos Disc, we now have a pretty good idea what the Antikythera Mechanism did (model the movement of the sun, moon and stars to make a combined clock/calender) and possibly who made it (Hipparchus or one of his followers).

Just looking at what the mechanism looked like, it is astonishing that it is 2000 years old.

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