-
- 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
-
-
- Among the treasures of the Greek National Archaeological
Museum in Athens are the remains of the most complex scientific object
that has been preserved from antiquity. Corroded and crumbling from 2,000
years under the sea, its dials, gear wheels and inscribed plates present
the historian with a tantalizing problem. Because of them we may have to
revise many of our estimates of Greek science. By studying them we may
find vital clues to the true origins of that high scientific technology
which hitherto has seemed peculiar to our modern civilization, setting
it apart from all cultures of the past.
-
 From the evidence of the fragments
one can get a good idea of the appearance of the original object [<link>
see illustration on page 62]. Consisting of a box with dials on the outside
and a very complex assembly of gear wheels mounted within, it must have
resembled a well- made 18ih-century clock. Doors hinged to the box served
to protect the dials, and on all available surfaces of box, doors and dials
there were long Greek inscriptions describing the operation and construction
of the instrument. At least 20 gear wheels of the mechanism have been preserved,
including a very sophisticated assembly of gears that were mounted eccentrically
on a turntable and probably functioned as a sort of epicyclic or differential,
gear-system.
-
- 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 [<p63.htmsee illustration's on these two
pages]. 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 shrivelled. 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 [<http://www.giant.net.au/users/rupert/kythera/p63.htmthird
from right on preceding page]. 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 earlieruniform 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 13 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 mighthave
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.
-
-
- Updated: 9-28-98 by Rupert Russell <rupert@giant.net.au
http://www.giant.net.au/users/rupert/kythear/kythera3.htm
-
-
- For more fascinating ancient Greek technology... link
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