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[cwa-logo]
Features/Greece/Issue 108
The Antikythera Mechanism
July 22, 2021
14 mins read
An ancient Greek machine rewriting the history of technology
A seemingly unassuming lump of corroded bronze has confounded
investigators for more than a century, ever since it proved to
contain precision gearwheels that simply should not have existed in
the ancient Greek world. A new study, using cutting-edge techniques,
has now revealed what this machine could do, and how it did it, as
Tony Freeth explains.
A digital reconstruction of the Antikythera Mechanism, a gold
rectangular object with dials and gears.The discovery of the
Antikythera Mechanism revealed that the ancient Greeks had achieved a
level of technological sophistication previously undreamed of. But
while the remains of the machine clearly demonstrated its ingenuity,
understanding exactly what it did and how it did it has challenged
generations of scholars. Now fresh evidence has provided a new
understanding of the Mechanism's workings. Here, we see a digital
reconstruction of the front (on the left) and back (right) faces of
the new reconstruction, with an exploded diagram of its intricate
gearing. [Image: Tony Freeth 2020]
In spring 1900, a party of sponge divers took shelter from a violent
Mediterranean storm. When the storm subsided, they dived for sponges
in the local waters near the tiny island of Antikythera, between
Crete and mainland Greece. By chance, they found a wreck full of
ancient Greek treasures, triggering the first major underwater
archaeology operation in history. Overseen by a gunboat from the
Greek navy to deter looters, by early 1901 the divers had begun to
recover a wonderful array of ancient Greek goods - beautiful bronze
sculptures, superb glassware, jewellery, amphorae, furniture
fittings, and tableware.
* [Youth-Antikythera]
* [Philosopher-bronze-proc]
* [DSC_2850-1]
The ship probably sank in around 65 BC and was transporting a range
of striking objects, now in the National Archaeological Museum in
Athens, including this bronze statue of a youth, a bronze head of a
philosopher, and this glass bowl. (Not shown to scale). [Images: 2005
Tony Freeth]
They also found an undistinguished lump, the size of a large
dictionary, which was probably recovered because it looked green,
suggesting bronze. It was not considered to be anything remarkable at
the time. Now, though, it is recognised as by far the most important
object of high technology ever recovered from the ancient world: an
ancient Greek astronomical calculating machine, known as the
Antikythera Mechanism.
Images of the front and back covers and fragments of the Mechanism
creating using Polynomial Texture Mapping. Surviving fragments of the
Antikythera Mechanism that are particularly relevant for this study.
These are imaged using Polynomial Texture Mapping (PTM - a digital
imaging technique) with specular enhancement. The letters refer to
the official fragment designations, so the front and back of Fragment
A are shown to the left. [Image: Hewlett-Packard 2005]
Months after it was recovered, the object split apart, revealing tiny
gearwheels inside, around the size of coins. It was an astonishing
discovery: no one had even thought that such precision gearwheels
could exist in ancient Greece. Today, only a third of the original
Mechanism survives, split into 82 fragments - designated by letters
A-G and numbers 1-75. It is a fiendish 3D jigsaw puzzle, all jumbled
together, with incomplete and severely corroded components. Over the
years, various scholars have sought to use these fragmentary elements
to deduce the purpose of the machine. The latest to tackle this
challenge are a multidisciplinary team of scientists, of which I am
part: the University College London (UCL) Antikythera Research Team.
The team was created when imaging specialist Lindsay MacDonald and
materials scientist Adam Wojcik invited me to join UCL. We widened
our expertise by teaming up with Myrto Georgakopoulou, an
archaeometallurgist, plus two PhD students, horologist David Higgon
and physicist Aris Dacanalis. Both of our students made essential
contributions to our research. We have used new ideas and a close
examination of all the data to challenge previous research and to
create the first model that satisfies all the evidence.
An astronomical calculating machine
From the beginning, the Mechanism generated controversy, with fierce
arguments about whether it was an astrolabe for tracking the stars or
a navigation device. Both proved to be wrong, but uncovering the
machine's secrets would be a long and difficult detective story,
peppered with major mistakes as well as surprising progress.
A PMT image of a fragment of the Mechanism with an inscription, the
relevant numbers are highlighted in red.Fragment 19, imaged using PTM
with specular enhancement. Highlighted are the numbers 76, 19, and
223, which represent the Moon-Sun cycles identified by Rehm. [Image:
Hewlett-Packard 2005]
The first real enlightenment came from a German philologist, Albert
Rehm, in the period from 1905. Buried in his unpublished research
notes are some extraordinary ideas. Rehm read inscriptions on the
Mechanism concerning the risings and settings of the stars as viewed
from Earth, and he found key astronomical cycles, too - 19-year and
76-year cycles of the Moon and a 223-month eclipse cycle. Rehm also
made the radical suggestion that the device was an astronomical
calculating machine. He had the groundbreaking idea that it contained
epicyclic gearing - that is, gears mounted on other gears - a level
of sophistication seemingly incredible for ancient Greece. In
addition, Rehm proposed that all five planets known in the ancient
world (Mercury, Venus, Mars, Jupiter, and Saturn) were displayed in a
ring system on the front of the Mechanism. He simply did not have
enough evidence to make coherent sense of his intuitions, and Rehm's
understanding of the internal mechanical structure was entirely
wrong. More than a century later, though, his astonishing ideas are
at the core of the new model of the machine created by the UCL
Antikythera Research Team.
Scientific investigations
Fifty years after Rehm and his struggle with inadequate data, a
British physicist, Derek de Solla Price, started a 20-year odyssey of
research that culminated in a famous paper Gears from the Greeks
(1974). He appreciated that to understand the Mechanism, there was a
pressing need for new data to guide him through the fragmentary and
confusing evidence.
Much of Price's progress was based on X-rays of the Mechanism
fragments, gathered and analysed by Charalambos and Emily Karakalos.
These enabled the identification of 30 surviving gears: 27 in
Fragment A and one in each of Fragments B, C, and D. Almost none of
the gears were complete, so they needed to estimate the all-important
number of teeth on each one - essential for understanding the
workings of a geared calculating machine. From these X-rays, Price
made a crucial discovery that the 19-year cycle of the Moon,
identified by Rehm in the inscriptions on the Mechanism, could be
calculated using its gearing.
* [Karakalos-Fragment-A-Teeth-Marked]
* [Derek-1]
An X-ray of Fragment A, taken by Charalambos Karakalos in 1970 (ABOVE
LEFT). The teeth of the gears have been marked in order to count the
number. Information from such X-rays allowed Derek de Solla Price to
create his model of the Antikythera Mechanism (ABOVE RIGHT). [Images:
The American Philosophical Society 1974 and Malcolm Kirk 1970]
Though Price made great progress, he also got much wrong, and only
made unresolved suggestions about the planets. When Price died in
1983, the challenge was taken up by Michael Wright, a curator of
Mechanical Engineering at London's Science Museum, who had extensive
experience of studying geared devices. While Price had discovered how
some of the Sun-Moon system worked, it was Wright who set about
reconstructing the gearing and a display for the planets.
Here, it is helpful to pause and consider how the ancient Greeks
perceived the Cosmos. Their view was (almost) entirely Earth-centred
and dominated by the mistaken belief that the Sun, Moon, and planets
all moved around the Earth, against a background of 'fixed stars'.
When seen from Earth, the planets appear to move against the backdrop
of the stars in perplexing ways. This is even reflected in the
ancient Greek origin for the modern word 'planet': planetai, meaning
'wandering'. Venus, for example, is sometimes ahead of the Sun and
sometimes behind when viewed from Earth. Mostly it seems to move
westwards through the sky, in the same direction as the Sun, but at
times Venus will stand still against the stars at a stationary point,
before looping backwards towards the east and reaching another
stationary point, then resuming westwards motion once more. This
synodic cycle - that is, its cycle relative to the Sun - is repeated
again and again. Similar motions are shared by all the planets,
creating a central problem for ancient astronomers. It was the
failure to appreciate that the planets move around the sun that made
the planetary motions seem so inexplicable.
In the 1st millennium BC, the Babylonians discovered what are known
as 'period relations' for the planets, which equated a whole number
of synodic cycles with a whole number of years. In the case of Venus,
for example, they found the period relation that the planet goes
through five synodic cycles in eight years. They could then use these
period relations to predict the future positions of the planets in
the sky. The ancient Greeks built on this by proposing geometrical
theories for explaining planetary motions. These theories were ideal
for mechanising the variable motions of the planets in a geared
calculating machine. It was a revolutionary idea: thanks to the
machine, the outcomes of ancient Greek astronomical theories could be
calculated with the simple turn of a handle.
The UCL team looked at the pioneering work by Wright. He found
evidence of bearings and other structures on the Main Drive Wheel.
This four-spoked gear is prominent at the front of Fragment A. It is
turned by the input handle and rotates once a year, thereby setting
all the other gears in motion. Wright judged that there must have
been an extensive epicyclic gearing system, mounted on the Main Drive
Wheel. On the basis of this evidence, he proposed that one of the
main purposes of the machine was to calculate the positions of the
planets, which were displayed at the front of the machine. Inspired
by astronomical clocks from the Middle Ages, Wright also introduced
devices known as a 'pin-and-slotted follower' mechanisms to his
reconstruction of the Antikythera Mechanism. When used alongside the
gears, these devices could be used to mimic the backward loops of the
planets. With great ingenuity, he managed to construct a planetarium
for the Mechanism, which tracked the date, Sun, Moon, and five
planets. He thought the outputs were shown as a system of pointers on
the front of the machine to indicate their positions in the Zodiac.
The publication of his results in 2002 was a landmark in Antikythera
research, even though multiple challenges to his model would
subsequently follow.
---------------------------------------------------------------------
This is an extract of an article that appeared in CWA 108. Read on in
the magazine (Click here to subscribe) or on our new website, The
Past, which offers all of the magazine's content digitally. At The
Past you will be able to read each article in full as well as the
content of our other magazines, Current Archaeology, Minerva, and
Military History Matters.
Tags:
* Ancient Greece
* Antikythera Mechanism
* technology
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