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Nothing like this instrument is preserved elsewhere. Nothing
comparable to it is known. from any ancient scientific text or
literary allusion. On the contrary, from all that we know of science
and technology in the Hellenistic Age we should have felt that such
a device could not exist. Some historians have suggested that the
Greeks were not interested in experiment because of a
contempt-perhaps induced by the existence of the institution of
slavery-for manual labor. On the other hand it has long been
recognized that in abstract mathematics and in mathematical
astronomy they were no beginners but rather "fellows of another
college" who reached great heights of sophistication. Many of
the Greek scientific devices known to us from written descriptions
show much mathematical ingenuity, but in all cases the purely
mechanical part of the design seems relatively crude. Gearing was
clearly known to the Greeks, but it was used only in relatively
simple applications. They employed pairs of gears to change angular
speed or mechanical ad- vantage, or to apply power through a right
angle, as in the water-driven mill.
Even the most complex mechanical devices described by the ancient
writers Hero of Alexandria and Vitruvius contained only simple
gearing. For example, the taximeter used by the Greeks to measure
the distance travelled by the wheels of a carriage employed only
pairs of gears (or gears and worms) to achieve the necessary ratio
of movement. It could be argued that if the Greeks knew the
principle of gearing, they should have had no difficulty in
constructing mechanisms as complex as epicyclic gears. We now know
from the fragments in the National Museum that the Greeks did make
such mechanisms, but the knowledge is so unexpected that some
scholars at first thought that the fragments must belong to some
more modern device.
Can we in fact be sure that the device is ancient? If we can, what
was its purpose? What can it tell us of the ancient world and of the
evolution of modern science? To authenticate the dating of the
fragments We must. tell the story of their discovery, which involves
the first (though inadvertent) adventure in underwater archaeology.
Just before Easter in 1900 a party of Dodecanese sponge-divers were
driven by storm to anchor near the tiny southern Greek island of
Antikythera (the accent is on the "kyth," pronounced to
rhyme with pith). There, at a depth of some 200 feet, they found the
wreck of an ancient ship. With the help of Greek archaeologists the
wreck was explored; several fine bronze and marble statues and other
objects were recovered. The finds created great excitement, but the
difficulties of diving without heavy equipment were immense, and in
September, 1901, the "dig' was abandoned. Eight months later
Valerios StaÎs, an archaeologist at the National Museum, was
examining some calcified lumps of corroded bronze that had been set
aside as possible pieces of broken statuary. Suddenly he recognized
among them the fragments of a mechanism.
It is now accepted that the wreck occurred during the first century
B.C. Gladys Weinberg of Athens has been kind enough to report to me
the results of several recent archaeological examinations of the
amphorae, pottery and minor objects from the ship. It appears from
her report that one might reason-ably date the wreck more closely as
65 B.C. ±15 years. Furthermore, since the identifiable objects come
from Rhodes and Cos, it seems that the ship may have. been voyaging
from these islands to Rome, perhaps without calling at the Greek
mainland.
The fragment that first caught the eye of StaÎs was one of the
corroded, inscribed plates that is an integral part of the
Antikythera mechanism, as the device later came to be called. StaÎs
saw immediately that the inscription was ancient. In the opinion of
the epigrapher Benjamin Dean Meritt, the forms of the letters are
those of the 'first century B.C.; they could hardly be older than
100 B.C. nor younger than the time of Christ. The dating is
supported by the content of the inscriptions. The words used and
their astronomical sense are all of this period. For example, the
most extensive and complete piece of inscription is part of a
parapegma (astronomical calendar) similar to that written by one
Geminos, who is thought to have lived in Rhodes about 77 B.C. We may
thus be reasonably sure that the mechanism did not find its way into
the wreck at some later period. Furthermore, it cannot have been
very old when it was taken aboard the ship as booty or merchandise.
As soon as the fragments had been discovered they were examined by
every available archaeologist; so began the long and difficult
process of identifying the mechanism and determining its function.
Some things were clear from the beginning. The unique importance of
the object was obvious, and the gearing was impressively complex.
From the inscriptions and the dials the mechanism was correctly
identified as an astronomical device. The first conjecture was that
it was some kind of navigating instrument – perhaps an astrolabe
(a sort of circular star-finder map also used for simple
observations). Some thought that it might be a small planetarium of
the kind that Archirnedes is said to have made. Unfortunately the
fragments were covered by a thick curtain of calcified material and
corrosion products, and these concealed so much detail that no one
could be sure of his conjectures or reconstructions. There was
nothing to do but wait for the slow and delicate work of the Museum
technicians in cleaning away this curtain. Meantime, as the work
proceeded, several scholars published accounts of all that was
visible, and through their labors a general picture of the mechanism
began to emerge. On the basis of new photographs made for me by the
Museum in 1955 I realized that the work of cleaning had reached a
point where it might at last be possible to take the work of
identification to a new level. Last summer, wilt the assistance of a
grant from the American Philosophical Society, I was able to visit
Athens and make a minute examination of the fragments. By good
fortune George Stamires, a Greek epigrapher, was there at the same
time; he was able to give me invaluable help by deciphering and
transcribing much more of the inscriptions than had been read
before. We are now in the position of being able to "join"
the fragments and to see how they fitted together in the original
machine and when they were brought up from the sea [see
illustration]. The success of this work has been most significant,
for previously it had been supposed that the various dials and
plates had been badly squashed together and distorted. It now
appears that most of the pieces are very nearly in their original
places, and that we have a much larger fraction of the complete
device than had been thought. This work also provides a clue to the
puzzle of why the fragments lay unrecognized until StaÎs saw them.
When they were found, the fragments were probably held together in
their original positions by the remains of the wooden frame of the
case. In the Museum the waterlogged wood dried and shriveled. The
fragments then fell apart, revealing the interior of the mechanism,
with its gears and inscribed plates. As a result of the new
examinations we shall in due course be able to publish a technical
account of the fragments and of the construction of the instrument.
In the meantime we can tentatively summarize some of these results
and show how they help to answer the question. What is it? There are
four ways of getting at the answer First, if we knew the details of
the mechanism, we should know what it did. Second, if we could read
the dials, we could tell what they showed. Third, if we could
understand the inscriptions, they might tell us about the mechanism.
Fourth, if we knew of any similar mechanism, analogies might be
helpful. All these approaches must be used, for none of them is
complete.
The geared wheels within the mechanism were mounted on a bronze
plate. On one side of the plate we can trace all the gear wheels of
the assembly and can determine, at least approximately, how many
teeth each had and how they meshed together. On the other side we
can do nearly as well, but we still lack vital links that would
provide a complete picture of the gearing. The general pattern of
the mechanism is nonetheless quite clear. An input was provided by
an axle that came through the side of the casing and turned a
crown-gear wheel. This moved a big, four-spoked driving-wheel that
was connected with two trains of gears that respectively led up and
down the plate and were connected by axles to gears on the other
side of the plate. On that side the gear-trains continued, leading
through an epicyclic turntable and coming eventually to a set of
shafts that turned the dial pointers. When the input axle was
turned, the pointers all moved at various speeds around their dials.
Certain structural features of the mechanism deserve special
attention. All the metal parts of the machine seem to have been cut
from a single sheet of low-tin bronze about two millimeters thick;
no parts were cast or made of another metal. There are indications
that the maker may have used a sheet made much earlier–uniform
metal plate of good quality was probably rare and expensive. All the
gear wheels have been made with teeth of just the same angle (60
degrees) and size, so that any wheel could mesh with any other.
There are signs that the machine was repaired at least twice; a
spoke of the driving wheel has been mended, and a broken tooth in a
small wheel has been replaced. This indicates that the machine
actually worked. The casing was provided with three dials, one at
the front and two at the back. The fragments of all of them are
still covered with pieces of the doors of the casing and with other
debris. Very little can be read on the dials, but there is hope that
they can be cleaned sufficiently to provide information that might
be decisive. The front dial is just clean enough to say exactly what
it did. It has two scales, one of which is fixed and displays the
names of the signs of the zodiac; the other is on a movable slip
ring and shows the months of the year. Both scales are carefully
marked off in degrees. The front dial fitted exactly over the main
driving-wheel, which seems to have turned the pointer by means of an
eccentric drum-assembly. Clearly this dial showed the annual motion
of the sun in the zodiac. By means of key letters inscribed on the
zodiac scale, corresponding to other letters on the parapegma
calendar plate, it also showed the main risings and settings of
bright stars and constellations throughout the year.
The back dials are more complex and less legible. The lower one had
three slip rings; the upper, four. Each had a little subsidiary dial
resembling the "seconds" dial of a watch. Each of the
large dials is inscribed with lines about every six degrees, and
between the lines there are letters and numbers. On the lower dial
the letters and numbers seem to record "moon, so many hours;
sun, so many hours"; we therefore suggest that this scale
indicates the main lunar phenomena of phases and times of rising and
setting. On the upper dial the inscriptions are much more crowded
and might well present information on the risings and settings,
stations and retrogradations of the planets known to the Greeks
(Mercury, Venus, Mars, Jupiter and Saturn).
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 fragments show that the original instrument carried at least
four large areas of inscription: outside the front door, inside the
back door, on the plate between the two back dials and on the
parapegma plates near the front dial. As I have noted, there are
also inscriptions around all the dials, and furthermore each part
and hole would seem to have had identifying letters so that the
pieces could be put together in the correct order and position. The
main inscriptions are in a sorry state and only short snatches of
them can be read. To provide an idea of their condition it need only
be said that in some cases a plate has completely disappeared,
leaving behind an impression of its letters, standing up in a mirror
image, in relief on the soft corrosion products on the plate below.
It is remarkable that such inscriptions can be read at all.
But even from the evidence of a few complete words one can get an
idea of the subject matter. The sun is mentioned several times, and
the planet Venus once; terms are used that refer to the stations and
retrogradations of planets; the ecliptic is named. Pointers,
apparently those of the dials, are mentioned. A line of one
inscription signfficantly records "76 years, 19 years."
This refers to the well-known Calippic cycle of 76 years, which is
four times the Metonic cycle of 19 years, or 235 synodic (lunar)
months. The next line includes the number "223," which
refers to the eclipse cycle of 223 lunar months.
Putting together the information gathered so far, it seems
reasonable to suppose that the whole purpose of the Antikythera
device was to mechanize just this sort of cyclical relation, which
was a strong feature of ancient astronomy. Using the cycles that
have been mentioned, one could easily design gearing that would
operate from one dial having a wheel that revolved annually, and
turn by this gearing a series of other wheels which would move
pointers indicating the sidereal, synodic and draconitic months.
Similar cycles were known for the planetary phenomena; in fact, this
type of arithmetical theory is the central theme of Seleucid
Babylonian astronomy, which was transmitted to the Hellenistic world
in the last few centuries B.C. Such arithmetical schemes are quite
distinct from the geometrical theory of circles and epicycles in
astronomy, which seems to have been essentially Greek. The two types
of theory were unified and brought to their peak in the second
century A.D. by Claudius Ptolemy, whose labors marked the triumph of
the new mathematical attitude toward geometrical models that still
characterizes physics today.
The Antikythera mechanism must therefore be an
arithmetical counterpart of the much more familiar geometrical
models of the solar system which were known to Plato and Archimedes
and evolved into the orrery and the planetarium. The mechanism is
like. a great astronomical clock without an escapement, or like a
modern analogue computer which uses mechanical parts to save tedious
calculation. It is a pity that we have no way of knowing whether the
device was turned automatically or by hand. It might have been held
in the hand and turned by a wheel at the side so that it would
operate as a computer, possibly for astrological use. I feel it is
more likely that it was permanently mounted, perhaps set in a
statue, and displayed as an exhibition piece. In that case it might
well have been turned by the power from a water clock or some other
device. Perhaps it is just such a wondrous device that was mounted
inside the famous Tower of Winds in Athens. It is certainly very
similar to the great astronomical cathedral clocks that were built
all over Europe during the Renaissance.
It is to the prehistory of the mechanical I clock that we must look
for important analogies the Antikythera mechanism and for an
assessment of its significance. Unlike other mechanical devices, the
clock did not evolve from the simple to the complex. The oldest
clocks of which we are well informed were the most complicated. All
the evidence points to the fact that the clock started as an
astronomical showpiece that happened also to indicate the time.
Gradually the timekeeping functions became more important and the
device that showed the marvelous clockwork of the heavens became
subsidiary. Behind the astronomical clocks of the 14th century there
stretches an unbroken sequence of mechanical models of astronomical
theory. At the head of this sequence is the Antikythera mechanism.
Following it are instruments and clocklike computers known from
Islam, from China and India and from the European Middle Ages. The
importance of this line is very great, because it was the tradition
of clock- making that preserved most of man's skill in scientific
fine mechanics. During the Renaissance the scientific
instrument-makers evolved from the clockmakers. Thus the Antikythera
mechanism is, in a way, the venerable progenitor of all our present
plethora of scientific hardware.
A significant passage in this story has to do with the astronomical
computers of Islam. Preserved complete at the Museum of History of
Science at Oxford is a 13th-century Islamic geared calendar-computer
that has various periods built into it, so that it shows on dials
the various cycles of the sun and moon. This design can be traced
back, with slightly different periods but a similar arrangement of
gears, to a manuscript written by the astronomer al-Biruni about
1000 A.D. Such instruments am much simpler than the Antikythera
mechanism, but they show so many points of agreement in technical
detail that it seems clear they came from a common tradition. The
same 60-degree gear teeth are used; wheels are mounted on square-shanked
axles; the geometrical layout of the gear assembly appears
comparable. It was just at this time that Islam was drawing on Greek
knowledge and rediscovering ancient Greek texts. It seems likely
that the Antikythera tradition was part of a large corpus of
knowledge that has since been lost to us but was known to the Arabs.
It was developed and transmitted by them to medieval Europe, where
it .became the foundation for the whole range of subsequent
invention in the field of clockwork.
On the one hand the Islamic devices knit the whole story together,
and demonstrate that it is through ancestry and not mere coincidence
that the Antikythera mechanism resembles a modern clock. On the
other hand they show that the Antikythera mechanism was no flash in
the pan but was a part of an important current in Hellenistic
civilization. History has contrived to keep that current dark to us,
and only the accidental underwater preservation of fragments that
would otherwise have crumbled to dust has now brought it to light.
It is a bit frightening to know that just before the fall of their
great civilization the ancient Greeks had come so close to our age,
not only in their thought, but also in their scientific technology.
Reconstruction of the mechanism by pr. Derek de
Solla Price, in collaboration
with the National Scientific Research Center Démokritos and the
physicist CH Karakalos. Image source:
Wikipedia
Rebuilding of the machine of Anticythère: it is the result of
research of the pr. Derek de Solla Price, in collaboration with the
National Scientific Research Center Démokritos and the physicist CH
Karakalos who carried out the x-ray tomography of the original and
the mechanism reconstituted to show their operation. Price built a
rectangular box of 0.33 X 0.17 X 0.10 m with plates of information
and protection, carrying Greek inscriptions of planets. The
mechanism is a complex set of 32 gears of various sizes, turning at
different speeds. The mechanism was offered by the pr. Price to the
national Museum in 1980 and remains the reference for the study of
the original despite the fact that its construction has been subject
to much criticism. National archaeological museum, Athens, n°BE
109/1980.
An ancient piece of clockwork shows the deep roots
of modern technology
WHEN a Greek sponge diver called Elias Stadiatos discovered the
wreck of a cargo ship off the tiny island of Antikythera in 1900, it
was the statues lying on the seabed that made the greatest
impression on him. He returned to the surface, removed his helmet,
and gabbled that he had found a heap of dead, naked women. The
ship's cargo of luxury goods also included jewellery, pottery, fine
furniture, wine and bronzes dating back to the first century BC. But
the most important finds proved to be a few green, corroded lumps—the
last remnants of an elaborate mechanical device.
The Antikythera mechanism, as it is now known, was originally
housed in a wooden box about the size of a shoebox, with dials on
the outside and a complex assembly of bronze gear wheels within.
X-ray photographs of the fragments, in which around 30 separate
gears can be distinguished, led the late Derek Price, a science
historian at Yale University, to conclude that the device was an
astronomical computer capable of predicting the positions of the sun
and moon in the zodiac on any given date. A new analysis, though,
suggests that the device was cleverer than Price thought, and
reinforces the evidence for his theory of an ancient Greek tradition
of complex mechanical technology.
Michael Wright, the curator of mechanical engineering at the
Science Museum in London, has based his new analysis on detailed
X-rays of the mechanism using a technique called linear tomography.
This involves moving an X-ray source, the film and the object being
investigated relative to one another, so that only features in a
particular plane come into focus. Analysis of the resulting images,
carried out in conjunction with Allan Bromley, a computer scientist
at Sydney University, found the exact position of each gear, and
suggested that Price was wrong in several respects.
In some cases, says Mr Wright, Price seems to have “massaged”
the number of teeth on particular gears (most of which are,
admittedly, incomplete) in order to arrive at significant
astronomical ratios. Price's account also, he says, displays
internal contradictions, selective use of evidence and unwarranted
speculation. In particular, it postulates an elaborate reversal
mechanism to get some gears to turn in the right direction.
Since so little of the mechanism survives, some guesswork is
unavoidable. But Mr Wright noticed a fixed boss at the centre of the
mechanism's main wheel. To his instrument-maker's eye, this was
suggestive of a fixed central gear around which other moving gears
could rotate. This does away with the need for Price's reversal
mechanism and leads to the idea that the device was specifically
designed to model a particular form of “epicyclic” motion.
The Greeks believed in an earth-centric universe and accounted
for celestial bodies' motions using elaborate models based on
epicycles, in which each body describes a circle (the epicycle)
around a point that itself moves in a circle around the earth. Mr
Wright found evidence that the Antikythera mechanism would have been
able to reproduce the motions of the sun and moon accurately, using
an epicyclic model devised by Hipparchus, and of the planets Mercury
and Venus, using an epicyclic model derived by Apollonius of Perga.
(These models, which predate the mechanism, were subsequently
incorporated into the work of Claudius Ptolemy in the second century
AD.)
A device that just modelled the motions of the sun, moon, Mercury
and Venus does not make much sense. But if an upper layer of
mechanism had been built, and lost, these extra gears could have
modelled the motions of the three other planets known at the time—Mars,
Jupiter and Saturn. In other words, the device may have been able to
predict the positions of the known celestial bodies for any given
date with a respectable degree of accuracy, using bronze pointers on
a circular dial with the constellations of the zodiac running round
its edge.
Mr Wright devised a putative model in which the mechanisms for
each celestial body stack up like layers in a sandwich, and started
building it in his workshop. The completed reconstruction, details
of which appeared in an article in the Horological Journal in May,
went on display this week at Technopolis, a museum in Athens. By
winding a knob on the side, celestial bodies can be made to advance
and retreat so that their positions on any chosen date can be
determined. Mr Wright says his device could have been built using
ancient tools because the ancient Greeks had saws whose teeth were
cut using v-shaped files—a task that is similar to the cutting of
teeth on a gear wheel. He has even made several examples by hand.
How closely this reconstruction matches up to the original will
never be known. The purpose of two dials on the back of the device
is still unclear, although one may indicate the year. Nor is the
device's purpose obvious: it may have been an astrological computer,
used to speed up the casting of horoscopes, though it might just as
easily have been a luxury plaything. But Mr Wright is convinced that
his epicyclic interpretation is correct, and that the original
device modelled the entire known solar system.
The Greeks had a word for it
That tallies with ancient sources that refer to such devices.
Cicero, writing in the first century BC, mentions an instrument “recently
constructed by our friend Poseidonius, which at each revolution
reproduces the same motions of the sun, the moon and the five
planets.” Archimedes is also said to have made a small
planetarium, and two such devices were said to have been rescued
from Syracuse when it fell in 212BC. This reconstruction suggests
such references can now be taken literally.
It also provides strong support for Price's theory. He believed
that the mechanism was strongly suggestive of an ancient Greek
tradition of complex mechanical technology which, transmitted via
the Arab world, formed the basis of European clockmaking techniques.
This fits with another, smaller device that was acquired in 1983 by
the Science Museum, which models the motions of the sun and moon.
Dating from the sixth century AD, it provides a previously missing
link between the Antikythera mechanism and later Islamic calendar
computers, such as the 13th century example at the Museum of the
History of Science in Oxford. That device, in turn, uses techniques
described in a manuscript written by al-Biruni, an Arab astronomer,
around 1000AD.
The origins of much modern technology, from railway engines to
robots, can be traced back to the elaborate mechanical toys, or
automata, that flourished in the 18th century. Those toys, in turn,
grew out of the craft of clockmaking. And that craft, like so many
other aspects of the modern world, seems to have roots that can be
traced right back to ancient Greece.
Part 2 >>
Source: Copyright © The
Economist Newspaper Limited 2002.
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