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Antikythera

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A clockwork type mechanism recovered in the Aegean Sea,

from a wreck that went down in approximately 82 B.C.,

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seems to indicate that ancient Greeks were far more

 technically sophisticated than historians had believed.

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The ancient Greeks were responsible for such marvels as the catapult and the camera obscura. They invented the astrolabe, a forerunner of the sextant, which aided marine navigation by (among other things) measuring the angle between the horizon and the sun or other celestial bodies. By the end of the first century B.C., they had even invented the odometer, which measured the distance a cart or carriage traveled. So when it comes to engineering, they were no slouches. When it comes to preserving their most advanced inventions for posterity... well, that's another story. At the beginning of the 20th century, historians were shocked to learn that Greek thinkers had built a rather sophisticated analog computer in the neighborhood of 82 B.C. and then, astonishingly, left no record of its existence.

 

Low Gear

In 1900, driven by a storm from their usual area of work, a crew of Greek sponge divers found themselves off the Aegean island of Antikythera, and decided that as long as they were there, they might as well dive and look for sponges. They anchored near the small island and what they found instead was the remains of a shipwreck from classical times, under about 42 meters (approximately 140 feet) of water. This ship, it was later surmised, was a Roman galley laden with Greek statues and other treasure: booty being taken back to the imperial capitol. Among the relics brought up from this shipwreck and taken to the Greek National Archeological Museum was a coral encrusted bronze mechanism.

 

Returning later with a navy ship, the divers recovered many artifacts from the sunken vessel, including marble and bronze statues. Archeologists who examined the pieces and other evidence reliably dated the shipwreck at around 65 B.C. (give or take 15 years). But one of the archeologists noticed that a clump of bronze contained what appeared to be gears—an astonishing discovery, since that would make it the world’s oldest surviving geared mechanism. Further examination showed that the object was originally in a wooden case holding about 32 bronze gears, with several dials on the outside. Over the centuries, the bronze had corroded, the wood had deteriorated, and the whole mass had accumulated heavy calcium deposits. But some inscriptions on bronze plates were still legible, and researchers began the painstaking task of reconstructing what the device must have looked like when it was made.

 

The first thorough description of the device—based solely on visual inspection and measurements—was published in 1959. Later evaluations included crucial additional details from X-ray and gamma-ray analysis, among other techniques. Taking all the available facts into account, the prevailing theory at the moment is that the device was a clockwork-like mechanism designed to display the progress and positions of the sun, moon, and probably all five of the other planets known at the time (Mercury, Venus, Mars, Jupiter, and Saturn) over a period of 19 years. In other words: it’s an analog astronomical computer. It had apparently been built several years before the shipwreck—most likely in 82 B.C.

 

It’s All About Us

That’s cool, but it gets even better. At the time the Antikythera mechanism was built, the Greeks still believed the entire universe revolved around the Earth. This caused tremendous problems for predicting the orbits of the planets, which from our perspective do not follow nice elliptical paths. So in order to make this mechanism account for the data, its designer had to invent entirely new arrangements of gears. One of these was the differential (a primitive version of what is found in modern cars)—which, until the discovery of the Antikythera mechanism, was believed to have been invented in the 13th century. As for the overall device, nothing similar is known to have existed until about A.D. 1000.


One reason historians find all this so interesting is that previously (in the absence of any reliable evidence to the contrary), the ancient Greeks were believed to have terrific theoretical knowledge when it came to astronomy, physics, and math, but little skill in the way of practical application. Sure, there were occasional remarks about an actual device. Cicero, for example, mentioned (at about the time the Antikythera mechanism was created) a device “recently constructed by our friend Poseidonius, which at each revolution reproduces the same motions of the sun, the moon and the five planets.” But since there was no evidence of these devices, few people took such claims literally. The discovery of the Antikythera mechanism changed all that.

 

We do not know for certain who created the device, nor do we know what its intended use was. It could conceivably have been a navigational aid, though that seems unlikely. It may have been used to create horoscopes, or as a teaching tool. It may even have been an elaborate toy designed for a rich patron.

 

The biggest mystery surrounding the Antikythera Mechanism, though, is why and how all records of this technology disappeared. Surely this could not have been the only such device ever created. If technology this important was in use at the time, it stands to reason that there would have been many other similar devices in existence, and that some of those would have survived to this day. But not only is this the only one, it’s a fluke that we even know about this one at all. What other ancient technologies may have existed that we don’t know about? The answers are probably lying out there - right where you’d least expect them.

 

In 1958 Dr. Derek J. de Solla Price successfully reconstructed the machine's appearance and use. The gearing system calculated the annual movements of the sun and moon. The arrangement shows that the gears could be moved forward and backward with ease at any speed. The device was thus not a clock but more like a calculator that could show the positions of the heavens past, present and future.

 

 

 

"The device is on display in the National Archaeological Museum in Athens. There is a one line explanation saying something like "computer from Anti-Kythera". A huge understatement if you ask me."

This is a gamma radiograph of one of the fragments ("A") of the mechanism. The gears can be matched with their positions in the gearplane. The three concentric bands at the lower left are part of the display dials on the back of the mechanism, whose function is not completely understood.

A Reconstruction of the Antikythera Mechanism from a few years ago by John Gleave, an orrery* maker based in the United Kingdom, decided to construct a working replica of the original mechanism.


* Named after Charles Boyle, Earl of Orrery (1676-1731), a mechanical apparatus which illustrates with balls of various sizes the relative motions and positions of the earth, moon, sun, etc.

The Antikythera Mechanism

 

It was not clear initially what the device was, except that it was clearly a sophisticated mechanism. X-ray analysis was subsequently used to probe the inner structure of the device, the details of the gears. Finally in 1974, a full analysis was published by Professor D. De Solla Price. While some of the original gearing was missing, there was enough to work out that the device was intended to show the motion of the Moon, Sun, and most likely the Planets through the years, when the handle was turned.

 

The sun gear has 64 teeth. It meshes with the smaller of a 38,48 gear pair. The 48 meshes with the smaller of a 24,127 gear pair. The 127 meshes with the 32 teeth of the moon gear. The ratio of angular speeds can then be calculated as:

 

64 48

127

254

÷ x ÷ x ÷ = ÷
38 24 32 19
     

=  13.36842..

which is an excellent approximation of the astronomical ratio 13.368267..

 

See also Fractions, Cycles, and Time

 

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This image (right) shows the operation of the Sun-Moon assembly, with a somewhat fanciful simulation of the display. In the actual device, the zodiac constellations were represented by their Greek names ("Libra" and the end of "Virgo" are decipherable in the relic). The constellation-schemata used here are imitations of the more accurate versions in Find the Constellations by H. A. Rey, Houghton-Mifflin Co., Boston, 1988. Java animation: (by Bill Casselman, University of British Columbia)..

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