Analog Computer from the Year 82 BC

In 1901 divers working off the isle of Antikythera found the remains of a clocklike mechanism 2,000 years old. The mechanism now appears to have been a device for calculating the motions of stars and planets … [ From June 1959 Scientific American p.60-7 ] _

The bronze mechanism had been lying in seawater for about 2,000 years, and was in poor mechanical shape. Only through the miracle of modern imaging technologies have scientists been able to slowly work out the nature and mechanical properties of this device.

Image: Nature

Two thousand years ago, a Greek mechanic set out to build a machine that would model the workings of the known Universe. The result was a complex clockwork mechanism that displayed the motions of the Sun, Moon and planets on precisely marked dials. By turning a handle, the creator could watch his tiny celestial bodies trace their undulating paths through the sky.

The mechanic’s name is now lost. But his machine, dubbed the Antikythera mechanism, is by far the most technologically sophisticated artefact that survives from antiquity. _

The Antikythera mechanism is far more sophisticated than any other device from that early in antiquity. A thousand years later Chinese engineer Su Song built a complex astronomical clock incorporating an escapement mechanism. Another 300 years passed before Europeans built complex mechanical clocks.

Some of the technical details of the dials are especially interesting. The front dial provides the only known extensive specimen from antiquity of a scientifically graduated instrument. When we measure the accuracy of the graduations under the microscope, we find that their average error over the visible 45 degrees is about a quarter of a degree. The way in which the error varies suggests that the arc was first geometrically divided and then subdivided by eye only. Even more important, this dial may give a means of dating the instrument astronomically. The slip ring is necessary because the old Egyptian calendar, having no leap years, fell into error by 1/4 day every year; the month scale thus had to be adjusted by this amount. As they are preserved the two scales of the dial are out of phase by 13½ degrees. Standard tables show that this amount could only occur in the year 80 B.C. and (because we do not know the month) at all years just 120 years (i.e., 30 days divided by 1/4 day per year) before or after that date. Alternative dates are archaeologically unlikely: 200 B.C. is too early; 40 A.D. is too late. Hence, if the slip ring has not moved from its last position, it was set in. 80 B.C. Furthermore, if we are right in supposing that a fiducial mark near the month scale was put there originally to provide a means of setting that scale in case of accidental movement, we can tell more. This mark is exactly 1/2 degree away from the present position of the scale, and this implies that the mark was made two years before the setting. Thus, although the evidence is by no means conclusive, we are led to suggest that the instrument was made about 82 B.C., used for two years (just long enough for the repairs to have been needed) and then taken onto the ship within the next 30 years. _

The Antikythera mechanism was discovered — after being lost and forgotten for 1,000 years — only by accident. Its workings were explained only through painstaking scientific reasoning using sophisticated modern x-ray imaging. What other complex mechanisms or designs from that age — or a previous age — have been lost to the depredations of time?

More: If you are the happy inventor of a before-its-time innovation, be sure to document your discovery as well as possible — so it will not be lost to future civilisations. Consider using “billion year data discs” to archive your work, just to be sure.

Bibliography of publications dealing with the Antikythera mechanism


A brief look at astronomical clocks

Online look at basic mechanisms

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2 Responses to Analog Computer from the Year 82 BC

  1. Pingback: Analog Computer from the Year 82 BC | High on Science & Tech - H.O.S.T

  2. Matt Musson says:

    Looks like a 2000 year old Rolex.

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