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Title: On the Origin of Clockwork, Perpetual Motion Devices, and the
Compass

Author: Derek J. de Solla Price

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Contributions from
The Museum of History and Technology:
Paper 6

On the Origin of Clockwork,
Perpetual Motion Devices, and the Compass
Derek J. de Solla Price

POWER AND MOTION GEARING 83
MECHANICAL CLOCKS 84
PERPETUAL MOTION AND THE CLOCK BEFORE DE DONDI 108
THE MAGNETIC COMPASS AS A FELLOW-TRAVELER FROM CHINA 110

ON THE ORIGIN OF CLOCKWORK,
PERPETUAL MOTION DEVICES
AND THE COMPASS

By Derek J. de Solla Price

Ancestor of the mechanical clock has been thought by some
to be the sundial. Actually these devices represent two
different approaches to the problem of time-keeping. True
ancestor of the clock is to be found among the highly
complex astronomical machines which man has been
building since Hellenic times to illustrate the relative
motions of the heavenly bodies.
This study—its findings will be used in preparing the
Museum's new hall on the history of time-keeping—traces
this ancestry back through 2,000 years of history on three
continents.
The Author: Derek J. de Solla Price wrote this paper while
serving as consultant to the Museum of History and
Technology of the Smithsonian Institution's United States
National Museum.

In each successive age this construction, having become lost, is, by the Sun's
favour, again revealed to some one or other at his pleasure. (Sūrya Siddhānta, ed.
Burgess, xiii, 18-19.)

HE histories of the mechanical clock and the magnetic compass must
be accounted amongst the most tortured of all our efforts to understand
the origins of man's important inventions. Ignorance has too often been
replaced by conjecture, and conjecture by misquotation and the false

authority of "common knowledge" engendered by the repetition of
legendary histories from one generation of textbooks to the next. In what
follows, I can only hope that the adding of a strong new trail and the
eradication of several false and weaker ones will lead us nearer to a
balanced and integrated understanding of medieval invention and the
intercultural transmission of ideas.
For the mechanical clock, perhaps the greatest hindrance has been its
treatment within a self-contained "history of time measurement" in which
sundials, water-clocks and similar devices assume the natural role of
ancestors to the weight-driven escapement clock in the early 14th century.1
This view must presume that a generally sophisticated knowledge of
gearing antedates the invention of the clock and extends back to the
Classical period of Hero and Vitruvius and such authors well-known for
their mechanical ingenuities.
Furthermore, even if one admits the use of clocklike gearing before the
existence of the clock, it is still necessary to look for the independent
inventions of the weight-drive and of the mechanical escapement. The first
of these may seem comparatively trivial; anyone familiar with the raising of
heavy loads by means of ropes and pulley could surely recognize the
possibility of using such an arrangement in reverse as a source of steady
power. Nevertheless, the use of this device is not recorded before its
association with hydraulic and perpetual motion machines in the
manuscripts of Riḍwān, ca. 1200, and its use in a clock using such a
perpetual motion wheel (mercury filled) as a clock escapement, in the
astronomical codices of Alfonso the Wise, King of Castile, ca. 1272.
The second invention, that of the mechanical escapement, has presented one
of the most tantalizing of problems. Without doubt, the crown and foliot
type of escapement appears to be the first complicated mechanical
invention known to the European Middle Ages; it heralds our whole age of
machine-making. Yet no trace has been found either of a steady evolution of
such escapements or of their invention in Europe, though the astronomical
clock powered by a water wheel and governed by an escapement-like
device had been elaborated in China for several centuries before the first
appearance of our clocks. We must now rehearse a revised story of the
origin of the clock as it has been suggested by recent researches on the

history of gearing and on Chinese and other astronomical machines. After
this we shall for the first time present evidence to show that this story is
curiously related to that of the Perpetuum Mobile, one of the great chimeras
of science, that came from its medieval origin to play an important part in
more recent developments of energetics and the foundations of
thermodynamics.2 It is a curious mixture, all the more so because, tangled
inextricably in it, we shall find the most important and earliest references to
the use of the magnetic compass in the West. It seems that in revising the
histories of clockwork and the magnetic compass, these considerations of
perpetual motion devices may provide some much needed evidence.

Figure 1.—Framework Structure of the Astronomical Clock of
Giovanni de Dondi of Padua, A.D. 1364.

Power and Motion Gearing
It may be readily accepted that the use of toothed wheels to transmit power
or turn it through an angle was widespread in all cultures several centuries

before the beginning of our era. Certainly, in classical times they were
already familiar to Archimedes (born 287 B.C.),3 and in China actual
examples of wheels and moulds for wheels dating from the 4th century B.C.
have been preserved.4 It might be remarked that these "machine" gear
wheels are characterized by having a "round number" of teeth (examples
with 16, 24 and 40 teeth are known) and a shank with a square hole which
fits without turning on a squared shaft. Another remarkable feature in these
early gears is the use of ratchet-shaped teeth, sometimes even twisted
helically so that the gears resemble worms intermeshing on parallel axles.5
The existence of windmills and watermills testifies to the general
familiarity, from classical times and through the middle ages, with the use
of gears to turn power through a right angle.

Figure 2.—Astronomical Clock of de Dondi, showing gearing on the
dial for Mercury and escapement crown wheel. Each of the seven side
walls of the structure shown in figure 1 was fitted with a dial.

Granted, then, this use of gears, one must guard against any conclusion that
the fine-mechanical use of gears to provide special ratios of angular
movement was similarly general and widespread. It is customary to adduce
here the evidence of the hodometer (taximeter) described by Vitruvius (1st
century B.C.) and by Hero of Alexandria (1st century A.D.) and the
ingenious automata also described by this latter author and his Islamic
followers.6 One may also cite the use of the reduction gear chain in power
machinery as used in the geared windlass of Archimedes and Hero.
Unfortunately, even the most complex automata described by Hero and by
such authors as Riḍwān contain gearing in no more extensive context than
as a means of transmitting action around a right angle. As for the windlass
and hodometer, they do, it is true, contain whole series of gears used in
steps as a reduction mechanism, usually for an extraordinarily high ratio,
but here the technical details are so etherial that one must doubt whether
such devices were actually realized in practice. Thus Vitruvius writes of a
wheel 4 feet in diameter and having 400 teeth being turned by a 1-toothed
pinion on a cart axle, but it is very doubtful whether such small teeth,
necessarily separated by about 3/8 inch, would have the requisite
ruggedness. Again, Hero mentions a wheel of 30 teeth which, because of
imperfections, might need only 20 turns of a single helix worm to turn it!
Such statements behove caution and one must consider whether we have
been misled by the 16th-and 17th-century editions of these authors,
containing reconstructions now often cited as authoritative but then serving
as working diagrams for practical use in that age when the clock was
already a familiar and complex mechanism. At all events, even if one
admits without substantial evidence that such gear reduction devices were
familiar from Hellenistic times onwards, they can hardly serve as more than
very distant ancestors of the earliest mechanical clocks.

Mechanical Clocks
Before proceeding to a discussion of the controversial evidence which may
be used to bridge this gap between the first use of gears and the fully-

developed mechanical clock we must examine the other side of this gap.
Recent research on the history of early mechanical clocks has demonstrated
certain peculiarities most relevant to our present argument.

the european tradition

If one is to establish a terminus ante quem for the appearance of the
mechanical clock in Europe, it would appear that 1364 is a most reasonable
date. At that time we have the very full mechanical and historical material
concerning the horological masterpiece built by Giovanni de Dondi of
Padua,7 and probably started as early as 1348. It might well be possible to
set a date a few decades earlier, but in general as one proceeds backwards
from this point, the evidence becomes increasingly fragmentary and
uncertain. The greatest source of doubt arises from the confusion between
sundials, water-clocks, hand-struck time bells, and mechanical clocks, all of
which are covered by the term horologium and its vernacular equivalents.
Temporarily postponing the consideration of evidence prior to ca. 1350, we
may take Giovanni de Dondi as a starting point and trace a virtually
unbroken lineage from his time to the present day. One may follow the
spread of clocks through Europe, from large towns to small ones, from the
richer cathedrals and abbeys to the less wealthy churches.8 There is the
transition from the tower clocks—showpieces of great institutions—to the
simple chamber clock designed for domestic use and to the smaller portable
clocks and still smaller and more portable pocket watches. In mechanical
refinement a similar continuity may be noted, so that one sees the
cumulative effect of the introduction of the spring drive (ca. 1475),
pendulum control (ca. 1650), and the anchor escapement (ca. 1680). The
transition from de Dondi to the modern chronometer is indeed basically
continuous, and though much research needs to be done on special topics, it
has an historical unity and seems to conform for the most part to the general
pattern of steady mechanical improvement found elsewhere in the history of
technology.

Figure 3.—German Wall Clock, Probably About 1450, showing the
degeneration in complexity from that of de Dondi's clock.

Most remarkable however is the earliest period of this seemingly steady
evolution. Side by side with the advances made in the earliest period
extending for less than two centuries from the time of de Dondi one may
see a spectacular process of degeneration or devolution. Not only is de
Dondi's the earliest clock of which we have a full and trustworthy account,
it is also far more complicated than any other (see Figs. 1, 2) until
comparatively modern times! Moreover, it was not an exceptional freak.
There were others like it, and one cannot therefore reject as accidental this
process of degeneration that occurs at the very beginning of the certain
history of the mechanical clock in Europe.

On the basis of such evidence I have suggested elsewhere9 that the clock is
"nought but a fallen angel from the world of astronomy." The first great
clocks of medieval Europe were designed as astronomical showpieces, full
of complicated gearing and dials to show the motions of the Sun, Moon and
planets, to exhibit eclipses, and to carry through the involved computations
of the ecclesiastical calendar. As such they were comparable to the orreries
of the 18th century and to modern planetariums; that they also showed the
time and rang it on bells was almost incidental to their main function. One
must not neglect, too, that it was in their glorification of the rationality of
the cosmos that they had their greatest effect. Through milleniums of
civilization, man's understanding of celestial phenomena had been the very
pinnacle of his intellect, and then as now popular exhibition of this sort was
just as necessary, as striking, and as impressive. One does not have to go far
to see how the paraphernalia of these early great astronomical clocks had
great influence on philosophers and theologians and on poets such as Dante.
It is the thesis of this part of my argument that the ordinary time-telling
clock is no affiliate of the other simple time-telling devices such as
sundials, sand glasses and the elementary water clocks. Rather it should be
considered as a degenerate branch from the main stem of mechanized
astronomical devices (I shall call them protoclocks), a stem which can boast
a continuous history filling the gap between the appearance of simple
gearing and the complications of de Dondi. We shall return to the discussion
of this main stem after analyzing the very recently discovered parallel stem

from medieval China, which reproduced and incidental time telling. Of the
greatest significance, this stem reveals the crucial independent invention of
a mechanical escapement, a feature not found in the European stem in spite
of centuries of intensive historical research and effort.

the chinese tradition

For this section I am privileged to draw upon a thrilling research project
carried out in 1956 at the University of Cambridge by a team consisting of
Dr. Joseph Needham, Dr. Wang Ling, and myself.10 In the course of this
work we translated and commented on a series of texts most of which had
not hitherto been made available in a Western tongue and, though well
known in China, had not been recognized as important for their horological
content. The key text with which we started was the "Hsin I Hsiang Fa
Yao," or "New Design for a (mechanized) Armillary (sphere) and (celestial)
Globe," written by Su Sung in A.D. 1090. The very full historical and
technical description in this text enabled us to establish a glossary and basic
understanding of the mechanism that later enabled us to interpret a whole
series of similar, though less extensive texts, giving a history of prior
development of such devices going back to the introduction of this type of
escapement by I-Hsing and Liang Ling-tsan, in A.D. 725, and to what
seems to be the original of all these Chinese astronomical machines, that
built by Chang Hêng ca. A.D. 130. Filling the gaps between these
landmarks are several other similar texts, giving ample evidence that the
Chinese development is continuous and, at least from Chang Hêng
onwards, largely independent of any transmissions from the West.
So far as we can see, the beginning of the chain in China (as indeed in the
West) was the making of simple static models of the celestial sphere. An
armillary sphere was used to represent the chief imaginary circles (e.g.,
equator, ecliptic, meridians, etc.), or a solid celestial globe on which such
circles could be drawn, together with the constellations of the fixed stars.
The whole apparatus was then mounted so that it was free to revolve about
its polar axis and another ring or a casing was added, external and fixed, to
represent the horizon that provided a datum for the rising and setting of the
Sun and the stars.

In the next stage, reached very soon after this, the rotation of the model was
arranged to proceed automatically instead of by hand. This was done, we
believe, by using a slowly revolving wheel powered by dripping water and
turning the model through a reduction mechanism, probably involving gears
or, more reasonably, a single large gear turned by a trip lever. It did not
matter much that the time-keeping properties were poor in the long run; the
model moved "by itself" and the great wonder was that it agreed with the
observed heavens "like the two halves of a tally."
In the next, and essential, stage the turning of the water wheel was regulated
by an "escapement" mechanism consisting of a weighbridge and trip levers
so arranged that the wheel was held in check, scoop by scoop, while each
scoop was filled by the dripping water, then released by the weighbridge
and allowed to rotate until checked again by the trip-lever arrangement. Its
action was similar to that of the anchor escapement, though its period of
repose was much longer than its period of motion and, of course, its time-
keeping properties were controlled not only by the mechanics of the device
but also by the rate of flow of the dripping water.
The Chinese escapement may justifiably be regarded as a missing link, just
halfway between the elementary clepsydra with its steady flow of water and
the mechanical escapement in which time is counted by chopping its flow
into cycles of action, repeated indefinitely and counted by a cumulating
device. With its characteristic of saving up energy for a considerable period
(about 15 minutes) before letting it go in one powerful action, the Chinese
escapement was particularly suited to the driving of jackwork and other
demonstration devices requiring much energy but only intermittent activity.
In its final form, as built by Su Sung after many trials and improvements,
the Chinese "astronomical clocktower" must have been a most impressive
object. It had the form of a tower about 30 feet high, surmounted by an
observation platform covered with a light roof (see fig. 4). On the platform
was an armillary sphere designed for observing the heavens. It was turned
by the clockwork so as to follow the diurnal rotation and thus avoid the
distressing computations caused by the change of coordinates necessary
when fixed alt-azimuth instruments were used. Below the platform was an
enclosed chamber containing the automatically rotated celestial globe
which so wonderfully agreed with the heavens. Below this, on the front of

the tower was a miniature pagoda with five tiers; on each tier was a
doorway through which, at due moment, appeared jacks who rang bells,
clanged gongs, beat drums, and held tablets to announce the arrival of each
hour, each quarter (they used 100 of them to the day) and each watch of the
night. Within the tower was concealed the mechanism; it consisted mainly
of a central vertical shaft providing power for the sphere, globe, and
jackwheels, and a horizontal shaft geared to the vertical one and carrying
the great water wheel which seemed to set itself magically in motion at
every quarter. In addition to all this were the levers of the escapement
mechanism and a pair of norias by which, once each day, the water used
was pumped from a sump at the bottom to a reservoir at the top, whence it
descended to work the wheel by means of a constant level tank and several
channels.
There were many offshoots and developments of this main stem of Chinese
horology. We are told, for example, that often mercury and occasionally
sand were used to replace the water, which frequently froze in winter in
spite of the application of lighted braziers to the interior of the machines.
Then again, the astronomical models and the jackwork were themselves
subject to gradual improvement: at the time of I-Hsing, for example, special
attention was paid to the demarcation of ecliptic as well as the normal
equatorial coordinates; this was clearly an influx from Hellenistic-Islamic
astronomy, in which the relatively sophisticated planetary mathematics had
forced this change not otherwise noted in China.
By the time of the Jesuits, this current of Chinese horology, long since
utterly destroyed by the perils of wars, storms, and governmental reforms,
had quite been forgotten. Matteo Ricci's clocks, those gifts that aroused so
much more interest than European theological teachings, were obviously
something quite new to the 16th-century Chinese scholars; so much so that
they were dubbed with a quite new name, "self-sounding bells," a direct
translation of the word "clock" (glokke). In view of the fact that the
medieval Chinese escapement may have been the basis of European
horology, it is a curious twist of fate that the high regard of the Chinese for
European clocks should have prompted them to open their doors, previously
so carefully and for so long kept closed against the foreign barbarians.

Figure 4.—Astronomical Clock Tower of Su Sung in K'ai-feng, ca.
A.D. 1090, from an original drawing by John Christiansen. (Courtesy of
Cambridge University Press.)

Mechanized Astronomical Models
Now that we have seen the manner in which mechanized astronomical
models developed in China, we can detect a similar line running from
Hellenistic time, through India and Islam to the medieval Europe that
inherited their learning. There are many differences, notably because of the
especial development of that peculiar characteristic of the West,
mathematical astronomy, conditioned by the almost accidental conflux of
Babylonian arithmetical methods with those of Greek geometry. However,
the lines are surprisingly similar, with the exception only of the crucial

invention of the escapement, a feature which seems to be replaced by the
influx of ideas connected with perpetual motion wheels.

hellenistic period

Most interesting and frequently cited is the bronze planetarium said to have
been made by Archimedes and described in a tantalisingly fragmentary
fashion by Cicero and by later authors. Because of its importance as a
prototype, we give the most relevant passages in full.11
Cicero's descriptions of Archimedes' planetarium are (italics supplied):
Gaius Sulpicius Gallus ... at a time when ... he happened to be at the house of Marcus Marcellus, his
colleague in the consulship [166 B.C.], ordered the celestial globe to be brought out which the
grandfather of Marcellus had carried off from Syracuse, when that very rich and beautiful city was
taken [212 B.C.].... Though I had heard this globe (sphaerae) mentioned quite frequently on account
of the fame of Archimedes, when I saw it I did not particularly admire it; for that other celestial
globe, also constructed by Archimedes, which the same Marcellus placed in the temple of Virtue, is
more beautiful as well as more widely known among the people. But when Gallus began to give a
very learned explanation of the device, I concluded that the famous Sicilian had been endowed with
greater genius than one would imagine possible for human being to possess. For Gallus told us that
the other kind of celestial globe, which was solid and contained no hollow space, was a very early
invention, the first one of that kind having been constructed by Thales of Miletus, and later marked
by Eudoxus of Cnidus—a disciple of Plato, it was claimed—with constellations and stars which are
fixed in the sky. He also said that many years later Aratus ... had described it in verse.... But this
newer kind of globe, he said, on which were delineated the motions of the sun and moon and of those
five stars which are called wanderers, or, as we might say, rovers [i. e., the five planets], contained
more than could be shown on the solid globe, and the invention of Archimedes deserved special
admiration because he had thought out a way to represent accurately by a single device for turning
the globe, those various and divergent movements with their different rates of speed. And when
Gallus moved [i.e., set in motion] the globe, it was actually true that the moon was always as many
revolutions behind the sun on the bronze contrivance as would agree with the number of days it was
behind in the sky. Thus the same eclipse of the sun happened on the globe as would actually happen,
and the moon came to the point where the shadow of the earth was at the very time when the sun
(appeared?) out of the region ... [several pages are missing in the manuscript; there is only one].
De republica, I, xiv (21-22), Keyes' translation.

When Archimedes put together in a globe the movements of the moon, sun and five wandering
[planets], he brought about the same effect as that which the god of Plato did in the Timaeus when he
made the world, so that one revolution produced dissimilar movements of delay and acceleration.
Tusculanae disputationes, I, 63.

Later descriptions from Ovid, Lactantius, Claudian, Sextus Empiricus, and
Pappus, respectively, are (italics supplied):

There stands a globe suspended by a Syracusan's skill in an enclosed bronze [frame, or sphere—or
perhaps, in enclosed air], a small image of the immense vault [of heaven]; and the earth is equally
distant from the top and bottom; that is brought about by its [i. e., the outer bronze globe's] round
form. The form of the temple [of Vesta] is similar....
Ovid, Fasti (1st century, A.D.), VI, 277-280, Frazer's translation.

The Sicilian Archimedes, was able to make a reproduction and model of the world in concave brass
(concavo aere similitudinem mundi ac figuram); in it he so arranged the sun and moon and
resembling the celestial revolutions (caelestibus similes conversionibus); and while it revolved it
exhibited not only the accession and recession of the sun and the waxing and waning of the moon
(incrementa deminutionesque lunae), but also the unequal courses of the stars, whether fixed or
wandering.
Lactantius, Institutiones divinae (4th century, A.D.), II, 5, 18.

Archimedes' sphere. When Jove looked down and saw the heavens figured in a sphere of glass, he
laughed and said to the other gods: "Has the power of mortal effort gone so far? Is my handiwork
now mimicked in a fragile globe?" An old man of Syracuse had imitated on earth the laws of the
heavens, the order of nature, and the ordinances of the gods. Some hidden influence within the sphere
directs the various courses of the stars and actuates the lifelike mass with definite motions. A false
zodiac runs through a year of its own and a toy moon waxes and wanes month by month. Now bold
invention rejoices to make its own heaven revolve and sets the stars [planets?] in motion by human
wit....
Claudian, Carmina minora (ca. A.D. 400), LI (LXVIII), Platnaure's translation.

The things that move by themselves are more wonderful than those which do not. At any rate, when
we behold an Archimedean sphere in which the sun and the rest of the stars move, we are immensely
impressed by it, not by Zeus because we are amazed at the wood, or at the movements of these
[bodies], but by the devices and causes of the movements.
Sextus Empiricus, Adversus mathematicos (3rd century, A.D.), IX, 115, Epps' translation.

Mechanics understand the making of spheres and know how to produce a model of the heavens (with
the courses of the stars moving in circles?) by mean of equal and circular motions of water, and
Archimedes the Syracusan, according to some, knows the cause and reasons for all of these.
Pappus (3rd century, A.D.), Works (Hultsch edition), VIII, 2, Epps' translation.

A similar arrangement seems to be indicated in another mechanized globe,
also mentioned by Cicero and said to have been made by Posidonius:
But if anyone brought to Scythia or Britain the globe (sphaeram) which our friend Posidonius [of
Apameia, the Stoic philosopher] recently made, in which each revolution produced the same
(movements) of the sun and moon and five wandering stars as is produced in the sky each day and
night, who would doubt that it was by exertion of reason?... Yet doubters ... think that Archimedes
showed more knowledge in producing movements by revolutions of a globe than nature (does) in
effecting them though the copy is so infinitely inferior to the original....

De natura deorum, II, xxxiv-xxxv (88), Yonge's translation.

In spite of the lack of sufficient technical details in any case, these
mechanized globe models, with or without geared planetary indicators
(which would make them highly complex machines), bear a striking
resemblance to the earliest Chinese device described by Chang Hêng.
One must not reject the possibility that transmission from Greece or Rome
could have reached the East by the beginning of the 2nd century, A.D.,
when he was working. It is an interesting question, but even if such contact
actually occurred, very soon afterwards, as we shall see, the western and
eastern lines of evolution parted company and evolved so far as can be
seen, quite independently until at least the 12th century.

The next Hellenistic source of which we must take note is a fragmentary
and almost unintelligible chapter in the works of Hero of Alexandria. Alone
and unconnected with his other chapters this describes a model which
seems to be static, in direct contrast to all other devices which move by
pneumatic and hydrostatic pressures; it may well be conjectured that in its
original form this chapter described a mechanized rather than a static globe:
The World represented in the Centre of the Universe: The construction of a transparent globe
containing air and liquid, and also of a smaller globe, in the centre, in imitation of the World. Two
hemispheres of glass are made; one of them is covered with a plate of bronze, in the middle of which
is a round hole. To fit this hole a light ball, of small size, is constructed, and thrown into the water
contained in the other hemisphere: the covered hemisphere is next applied to this, and, a certain
quantity of the liquid having been removed from the water, the intermediate space will contain the
ball; thus by the application of the second hemisphere what was proposed is accomplished.
Pneumatics, XLVI, Woodcroft's translation.

It will be noted that these earliest literary references are concerned with
pictorial, 3-dimensional models of the universe, moved perhaps by hand,
perhaps by waterpower; there is no evidence that they contained
complicated trains of gears, and in the absence of this we may incline to the
view that in at least the earliest such models, gearing was not used.
The next developments were concerned on the one hand with increasing the
mathematical sophistication of the model, on the other hand with its
mechanical complexity. In both cases we are most fortunate in having
archaeological evidence which far exceeds any literary sources.

The mathematical process of mapping a sphere onto a plane surface by
stereographic projection was introduced by Hipparchus and had much
influence on astronomical techniques and instruments thereafter. In
particular, by the time of Ptolemy (ca. A.D. 120) it had led to the successive
inventions of the anaphoric clock and of the planispheric astrolabe.12 Both
these devices consist of a pair of stereographic projections, one of the
celestial sphere with its stars and ecliptic and tropics, the other of the lines
of altitude and azimuth as set for an observer in a place at some particular
latitude.
In the astrolabe, an openwork metal rete containing markings for the stars,
etc., may be rotated by hand over a disc on which the lines of altitude and
azimuth are inscribed. In the anaphoric clock a disc engraved with the stars
is rotated automatically behind a fixed grille of wires marking lines of
altitude and azimuth. Power for rotating the disc is provided by a float
rising in a clepsydra jar and connected, by a rope or chain passing over a
pulley to a counterweight or by a rack and pinion, to an axle which
supported the rotating disc and communicated this motion to it.13

Figure 5. Plate of Salzburg Anaphoric Clock, a reconstruction (see
footnote 14) based on a photograph of the remaining fragment. (Courtesy
of Oxford University Press.)

Parts of two such discs from anaphoric clocks have been found, one at
Salzburg14 and one at Grand in the Vosges,15 both of them dating from the
2nd century A.D. Fortunately there is sufficient evidence to reconstruct the
Salzburg disc and show that it must have been originally about 170 cm. in
diameter, a heavy sheet of bronze to be turned by the small power provided
by a float, and a large and impressive device when working (see fig. 5).
Literary accounts of the anaphoric clock have been analyzed by

Drachmann; there is no evidence of the representation of planets moved
either by hand or by automatic gearing, only in the important case of the
sun was such a feature included of necessity. A model "sun" on a pin could
be plugged in to any one of 360 holes drilled in at equal intervals along the
band of the ecliptic. This pin could be moved each day so that the anaphoric
clock kept step with the seasonal variation of the times of sunrise and sunset
and the lengths of day and night.
The anaphoric clock is not only the origin of the astrolabe and of all later
planetary models, it is also the first clock dial, setting a standard for
"clockwise" rotation, and leaving its mark in the rotating dial and stationary
pointer found on the earliest time-keeping clocks before the change was
made to a fixed dial and moving hand.
We come finally to a piece of archaeological evidence that surpasses all
else. Though badly preserved and little studied it might well be the most
important classical object ever found; entailing a complete re-estimation of
the technical prowess of the Hellenistic Greeks. In 1901 a sunken treasure
ship was discovered lying off the island of Antikythera, between Greece and
Crete.16 Many beautiful classical works of statuary were recovered from it,
and these are now amongst the greatest treasures of the National Museum at
Athens, Greece. Besides these obviously desirable art relics, there came to
the surface some curious pieces of metal, accompanied by traces of what
may have been a wooden casing. Two thousand years under the sea had
reduced the metal to a mess of corroded fragments of plates, powdered
verdigris, and still recognizable pieces of gear wheels.
If it were not for the established dates for other treasure from this ship,
especially the minor objects found, and for traces of inscriptions on this
metal device written in letters agreeing epigraphically with the other
objects, one would have little doubt in supposing that such a complicated
piece of machinery dated from the 18th century, at the earliest. As it is,
estimates agree on ca. 65 B.C. ±10 years, and we can be sure that
the machine is of Hellenistic origin, possibly from Rhodes or Cos.

Figure 6.—Antikythera Machine, Largest Fragment. (Photo courtesy
of National Museum, Athens.)

The inscriptions, only partly legible, lead one to believe that we are dealing
with an astronomical calculating mechanism of some sort. This is born out
by the mechanical construction evident on the fragments. The largest one
(fig. 6) contains a multiplicity of gearing involving an annular gear working
epicyclic gearing on a turntable, a crown wheel, and at least four separate
trains of smaller gears, as well as a 4-spoked driving wheel. One of the
smaller fragments (fig. 7, bottom) contains a series of movable rings which
may have served to carry movable scales on one of the three dials. The third
fragment (fig. 7, top) has a pair of rings carefully engraved and graduated in
degrees of the zodiac (this is, incidentally, the oldest engraved scale known,
and micrometric measurements on photographs have indicated a maximum
inaccuracy of about 1/2° in the 45° present).

Figure 7.—Antikythera Machine, Two Smaller Fragments. (Photo
courtesy of National Museum, Athens.)

Unfortunately, the very difficult task of cleaning the fragments is slow, and
no publication has yet given sufficient detail for an adequate explanation of
this object. One can only say that although the problems of restoration and
mechanical analysis are peculiarly great, this must stand as the most
important scientific artifact preserved from antiquity.
Some technical details can be gleaned however. The shape of the gear teeth
appears to be almost exactly equilateral triangles in all cases (fig. 8), and
square shanks may be seen at the centers of some of the wheels. No wheel
is quite complete enough for a count of gear teeth, but a provisional
reconstruction by Theophanidis (fig. 9) has shown that the appearances are
consistent with the theory that the purpose of the gears was to provide the
correct angular ratios to move the sun and planets at their appropriate
relative speeds.

Figure 8.—Antikythera Machine, Detail From Figure 6, showing
gearing. (Photo courtesy of National Museum, Athens.)

Thus, if the evidence of the Antikythera machine is to be taken at its face
value, we have, already in classical times, the use of astronomical devices
as complicated as any clock. In any case, the material supplied by the works
ascribed to Archimedes, Hero, and Vitruvius, and the more certain evidence
of the anaphoric clocks is sufficient to show that there was a strong classical
tradition of such machines, a tradition that inspired, even if it did not
directly influence, later developments in Islam and Europe on the one side,
and, just possibly, China on the other.

Note added in proof:

Since the above lines were written, I have been privileged to make a full examination
of the fragments in the National Museum in Athens. As a result we can read much more
inscription and make out many more details of the mechanism. The cleaning and
disentangling of the fragments by the museum staff has proceeded to the stage where
one can assert much more positively that the device was an astronomical computer for
sidereal, solar, lunar, and possibly also planetary phenomena. (See my article in the
Scientific American, June 1959, vol. 200, No. 6, pp. 60-67.) Relevant to the present
study, it must also be noted at this point that the machine is now shown to be strongly
related to the geared astrolabe of al-Biruni and thereby the Hellenistic, Islamic, and
European developments are drawn together even more tightly.

Let us now turn our attention to those civilizations which were
intermediaries, geographically and culturally, between Greece and medieval
Europe, and between both of these and China. From India there are only
two references, very closely related and appearing in the best known
astronomical texts in connection with descriptions of the armillary sphere
and celestial globe. These texts are both quite garbled, but so far as one may
understand them, it seems that the types of spheres and globes mentioned
are more akin to those current in China than in the West. The relevant
portions of text are as follows (italics supplied):
The circle of the horizon is midway of the sphere. As covered with a casing and as left uncovered, it
is the sphere surrounded by Lokāloka [the mountain range which formed the boundary of the
universe in puranic geography]. By the application of water is made ascertainment of the revolution
of time. One may construct a sphere-instrument combined with quicksilver: this is a mystery; if
plainly described, it would be generally intelligible in the world. Therefore let the supreme sphere be
constructed according to the instruction of the preceptor [guru]. In each successive age this
construction, having become lost, is, by the Sun's favour, again revealed to some one or other, at his
pleasure. So also, one should construct instruments in order to ascertain time. When quite alone, one
should apply quicksilver to the wonder-causing instrument. By the gnomon, staff, arc, wheel,
instruments for taking the shadow of various kinds.... By water-instruments, the vessel, by the
peacock, man, monkey, and by stringed sand-receptacles one may determine time accurately.
Quicksilver-holes, water, and cords, and oil and water, mercury and sand are used in these: these
applications, too, are difficult.
Sūrya Siddhānta, xiii, 15-22,
E. Burgess' translation, New Haven, 1860.

Figure 9.—Antikythera Machine, Partial Reconstruction by
Theophanidis (see footnote 16).

A self-revolving instrument [or swayanvaha yantra]: Make a wheel of light wood and in its
circumference put hollow spokes all having bores of the same diameter, and let them be placed at
equal distances from each other; and let them also be placed at an angle verging somewhat from the
perpendicular: then half fill these hollow spokes with mercury; the wheel thus filled will, when
placed on an axis supported by two posts, revolve of itself.
Or scoop out a canal in the tire of the wheel and then plastering leaves of the Tȧla tree over this canal
with wax, fill one half of this canal with water and the other half with mercury, till the water begins
to come out, and then cork up the orifice left open for filling the wheel. The wheel will then revolve
of itself, drawn around by the water.
Description of a syphon: Make up a tube of copper or other metal, and bend it in the form of an
Ankus'a or elephant hook, fill it with water and stop up both ends. And then putting one end into a

reservoir of water let the other end remain suspended outside. Now uncork both ends. The water of
the reservoir will be wholly sucked up and fall outside.
Now attach to the rim of the before described self-revolving wheel a number of water-pots, and place
the wheel and these pots like the water wheel so that the water from the lower end of the tube flowing
into them on one side shall set the wheel in motion, impelled by the additional weight of the pots thus
filled. The water discharge from the pots as they reach the bottom of the revolving wheel, should be
drawn off into the reservoir before alluded to by means of a water-course or pipe.
The self-revolving machine [mentioned by Lalla, etc.] which has a tube with its lower end open is a
vulgar machine on account of its being dependant, because that which manifests an ingenious and not
a rustic contrivance is said to be a machine.
And moreover many self-revolving machines are to be met with, but their motion is procured by a
trick. They are not connected with the subject under discussion. I have been induced to mention the
construction of these, merely because they have been mentioned by former astronomers.
Siddhānta Siromaṇi, xi, 50-57, L. Wilkinson's translation,
revised by Bȧpu̇ deva S(h)ȧstri, Calcutta, 1861.

Before proceeding to an investigation of the content of these texts it is of
considerable importance to establish dates for them, though there are many
difficulties in establishing any chronology for Hindu astronomy. The Sūrya
Siddhānta is known to date, in its original form, from the early Middle
Ages, ca. 500. The section in question is however quite evidently an
interpolation from a later recension, most probably that which established
the complete text as it now stands; it has been variously dated as ca. 1000 to
ca. 1150 A.D. The date of the Siddhānta Siromaṇi is more certain for we
know it was written in about 1150 by Bhāskara (born 1114). Thus both
these passages must have been written within a century of the great
clocktower made by Su Sung. The technical details will lead us to suppose
there is more than a temporal connection.
We have already noted that the armillary spheres and celestial globes
described just before these extracts are more similar in design to Chinese
than to Ptolemaic practice. The mention of mercury and of sand as
alternatives to water for the clock's fluid is another feature very prevalent in
Chinese but absent in the Greek texts. Both texts seem conscious of the
complexity of these devices and there is a hint (it is lost and revealed) that
the story has been transmitted, only half understood, from another age or
culture. It should also be noted that the mentions of cords and strings rather
than gears, and the use of spheres rather than planispheres would suggest

we are dealing with devices similar to the earliest Greek models rather than
the later devices, or with the Chinese practice.
A quite new and important note is injected by the passage from the
Bhāskara text. Obviously intrusive in this astronomical text we have the
description of two "perpetual motion wheels" together with a third,
castigated by the author, which helps its perpetuity by letting water flow
from a reservoir by means of a syphon and drop into pots around the
circumference of the wheel. These seem to be the basis also, in the extract
from the Sūrya Siddhānta, of the "wonder-causing instrument" to which
mercury must be applied.
In the next sections we shall show that this idea of a perpetual motion
device occurs again in conjunction with astronomical models in Islam and
shortly afterwards in medieval Europe. At each occurrence, as here, there
are echoes of other cultures. In addition to those already mentioned we find
the otherwise mysterious "peacock, man and monkey," cited as parts of the
jackwork of astronomical clocks of Islam, associated with the weight drive
so essential to the later horology in Europe.
We have already seen that in classical times there were already two
different types of protoclocks; one, which may be termed
"nonmathematical," designed only to give a visual aid in the conception of
the cosmos, the other, which may be termed "mathematical" in which
stereographic projection or gearing was employed to make the device a
quantitative rather than qualitative representation. These two lines occur
again in the Islamic culture area.
Nonmathematical protoclocks which are scarcely removed from the
classical forms appear continuously through the Byzantine era and in Islam
as soon as it recovered from the first shocks of its formation. Procopius
(died ca. 535) describes a monumental water clock which was erected in
Gaza ca. 500.17 It contained impressive jackwork, such as a Medusa head
which rolled its eyes every hour on the hour, exhibiting the time through
lighted apertures and showing mythological interpretations of the cosmos.
All these effects were produced by Heronic techniques, using hydraulic
power and puppets moved by strings, rather than with gearing.

Again in 807 a similarly marvelous exhibition clock made of bronze was
sent by Harun-al-Rashid to the Emperor Charlemagne; it seems to have
been of the same type, with automata and hydraulic works. For the
succeeding few centuries, Islam was in its Golden Age of development of
technical astronomy (ca. 950-1150) and attention may have been
concentrated on the more mathematical protoclocks. Towards the end of the
12th century, however, there was a revival of the old tradition, mainly at the
court of the Emperor Saladin (1146-1173) when a great automaton water
clock, more magnificent than any hitherto, was erected in Damascus. It was
rebuilt, after 1168, by Muḥammad b. 'Alī b. Rustum, and repaired and
improved by his son, Fakhr ad-dīn Riḍwān b. Muḥammad,18 who is most
important as the author of a book which describes in considerable technical
detail the construction of this and other protoclocks. Closely associated with
his book one also finds texts dealing with perpetual-motion devices, which
we shall consider later.
During the century following this horological exuberance in Damascus, the
center of gravity of Islamic astronomy shifted from the East to the Hispano-
Moorish West. At the same time there comes more evidence that the line of
mathematical protoclocks had not been left unattended. This is suggested by
a description given by Trithemius of another royal gift from East to West
which seems to have been different from the automata and hydraulic
devices of the tradition from Procopius to Riḍwān:19

In the same year [1232] the Saladin of Egypt sent by his ambassadors as a gift to the emperor
Frederic a valuable machine of wonderful construction worth more than five thousand ducats. For it
appeared to resemble internally a celestial globe in which figures of the sun, moon, and other planets
formed with the greatest skill moved, being impelled by weights and wheels, so that performing their
course in certain and fixed intervals they pointed out the hour night and day with infallible certainty;
also the twelve signs of the zodiac with certain appropriate characters, moved with the firmament,
contained within themselves the course of the planets.

The phrase "resembled internally" is of especial interest in this passage; it
may perhaps arise as a mistranslation of the technical term for stereographic
projection of the sphere, and if so the device might have been an anaphoric
clock or some other astrolabic device.

Figure 10.—Calendrical Gearing Designed by al-Biruni, ca. A.D.
1000. The gear train count is 40-10+7-59+19-59+24-48. The gear of 48
therefore makes 19 (annual) rotations while that of 19-59 shows 118
double lunations of 29+30=59 days. The gear of 40 shows a (lunar)
rotation in exactly 28 days, and the center pinions 7+10 rotate in exactly
one week. After Wiedemann (see footnote 20).

This is made more probable by the existence of a specifically Islamic
concentration on the astrolabe, and on its planetary companion instrument,
the equatorium, as devices for mechanizing computation by use of
geometrical analogues. The ordinary planispheric astrolabe, of course, was
known in Islam from its first days until almost the present time. From the
time of al-Biruni (ca. 1000)—significantly, perhaps, he is well known for
his travel account of India—there is remarkable innovation.

Most cogent to our purpose is a text, described for the first time by
Wiedemann,20 in which al-Biruni explains how a special train of gearing
may be used to show the revolutions of the sun and moon at their relative
rates and to demonstrate the changing phase of the moon, features of
fundamental importance in the Islamic (lunar) calendrical system. This
device necessarily uses gear wheels with an odd number of teeth (e.g., 7,
19, 59) as dictated by the astronomical constants involved (see fig. 10). The
teeth are shaped like equilateral triangles and square shanks are used,
exactly as with the Antikythera machine. Horse-headed wedges are used for
fixing; a tradition borrowed from the horse-shaped Farās used to fasten the
traditional astrolabe. Of special interest for us is the lunar phase diagram,
which is just the same in form and structure as the lunar volvelle that occurs
later in horology and is still so commonly found today, especially as a
decoration for the dial of grandfather clocks.

Figure 11.—Geared Astrolabe by Muḥammad b. Abī Bakr of Isfahan,
A.D. 1221-1222. (Photo courtesy of Science Museum, London.)

Biruni's calendrical machine is the earliest complicated geared device on
record and it is therefore all the more significant that it carries a feature
found in later clocks. From the manuscript description alone one could not
tell whether it was designed for automatic action or merely to be turned by
hand. Fortunately this point is made clear by the most happy survival of an
intact specimen of this very device, without doubt the oldest geared
machine in existence in a complete state.

Figure 12.—Gearing from Astrolabe Shown in Figure 11. The gear
train count is as follows: 48-13+8-64+64-64+10-60. The pinion of 8 has
been incorrectly replaced by a more modern pinion of 10. The gear of 48
should make 13 (lunar) rotations while the double gear of 64+64 makes 6
revolutions of double months (of 29-30 days) and the gear of 60 makes a
single turn in the hegiral year of 354 days. (Photo courtesy of Science
Museum, London.)

This landmark in the history of science and technology is now preserved at
the Museum of the History of Science, Oxford, England.21 It is an astrolabe,
dated 1221-22 and signed by the maker, Muḥammad b. Abī Bakr (died
1231-32) of Isfahan, Persia (see figs. 11 and 12). The very close
resemblance to the design of Biruni is quite apparent, though the gearing
has been simplified very cleverly so that only one wheel has an odd number
of teeth (13), the rest being much easier to mark out geometrically (e.g., 10,
48, 60, and 64 teeth). The lunar phase volvelle can be seen through the
circular opening at the back of the astrolabe. It is quite certain that no
automatic action is intended; when the central pivot is turned, by hand,
probably by using the astrolabe rete as a "handle," the calendrical circles
and the lunar phase are moved accordingly. Using one turn for a day would
be too slow for useful re-setting of the instrument, in practice a turn
corresponds more nearly to an interval of one week.

Figure 13.—Astrolabe Clock, Regulated by a Mercury Drum, from
the Alfonsine Libros del saber (see footnote 22).

In addition to this geared development of the astrolabe, the same period in
Islam brought forth a new device, the equatorium, a mechanical model

designed to simulate the geometrical constructions used for finding the
positions of the planets in Ptolemaic astronomy. The method may have
originated already in classical times, a simple device being described by
Proclus Diadochus (ca. 450), but the first general, though crude, planetary
equatorium seems to have been described by Abulcacim Abnacahm (ca.
1025) in Granada; it has been handed down to us in the archaic Castilian of
the Alfonsine Libros del saber.22 The sections of this book, dealing with the
Laminas de las VII Planetas, describe not only this instrument but also the
improved modification introduced by Azarchiel (born ca. 1029, died ca.
1087).
No Islamic examples of the equatorium have survived, but from this period
onward, there appears to have been a long and active tradition of them, and
ultimately they were transmitted to the West, along with the rest of the
Alfonsine corpus. More important for our argument is that they were the
basis for the mechanized astronomical models of Richard of Wallingford
(ca. 1320) and probably others, and for the already mentioned great
astronomical clock of de Dondi. In fact, the complicated gearwork and dials
of de Dondi's clock constitute a series of equatoria, mechanized in just the
same way as the calendrical device described by Biruni.
It is evident that we are coming nearer now to the beginning of the true
mechanical clock, and our last step, also from the Alfonsine corpus of
western Islam, provides us with an important link between the anaphoric
clock, the weight drive, and a most curious perpetual-motion device, the
mercury wheel, used as an escapement or regulator. The Alfonsine book on
clocks contains descriptions of five devices in all, four of them being due to
Isaac b. Sid (two sundials, an automaton water-clock and the present
mercury clock) and one to Samuel ha-Levi Adulafia (a candle clock)—they
were probably composed just before ca. 1276-77.

Figure 14.—Islamic Perpetual Motion Figure 15.—Another Perpetual Motion
Wheel, after manuscript cited by Schmeller Wheel, after the text cited in figure 14.
(see footnote 26).

The mercury clock of Isaac b. Sid consists of an astrolabe dial, rotated as in
the anaphoric clock, and fitted with 30 leaf-shaped gear teeth (see fig. 13).
These are driven by a pinion of 6 leaves mounted on a horizontal axle
(shown very diagrammatically in the illustration) and at the other end of
this axle is a wheel on which is mounted the special mercury drum which is
powered by a normal weight drive.
It is the mercury drum which forms the most novel feature of this device;
the fluid, constrained in 12 chambers so as to just fill 6 of them, must
slowly filter through small holes in the constraining walls. In practice, of
course, the top mercury surfaces will not be level, but higher on the right so
as to balance dynamically the moment of the applied weight on its driven
rope. This curious arrangement shows point of resemblance to the Indian
"mercury-holes," to the perpetual-motion devices found in the medieval
European tradition and also in the texts associated with Riḍwān, which we
shall next examine.
It is of the greatest interest to our theme that the Islamic contributions to
horology and perpetual motion seem to form a closely knit corpus. A most
important series of horological texts, including those of Riḍwān and al-
Jazarī, have been edited by Wiedemann and Hauser.23 Other Islamic texts
give versions of the water clocks and automata of Archimedes and of Hero
and Philo of Alexandria.24 In at least three cases25 these texts are found also

associated with texts describing perpetual-motion wheels and other
hydraulic devices. Three manuscripts of this type have been published in
German translation by Schmeller.26 The devices include a many chambered
wheel (see fig. 14) similar to the Alfonsine mercury "escapement," a wheel
of slanting tubes constructed like the noria (see fig. 15), wheels of weights
swinging on arms as described by Villard of Honnecourt, and a remarkable
device which seems to be the earliest known example of a weight drive.
This latter machine is a pump, in which a chain of buckets is used to raise
water by passing over a pulley which is geared to a drum powered by a
falling weight (see fig. 16); perhaps for balance, the whole arrangement is
made in duplicate with common axles for the corresponding parts.

Figure 16.—Islamic Pump Powered by a Weight Drive, after the text
cited in figure 14.

The Islamic tradition of water clocks did not involve the use of gears,
though very occasionally a pair is used to turn power through an angle
when this is dictated by the use of a water wheel in the automata. In the
main, everything is worked by floats and strings or by hydraulic or
pneumatic forces, as in Heros devices. The automata are very elaborate,
with figures of men, monkeys, peacocks, etc., symbolizing the passage of
hours.

medieval europe

Echoes from nearly all the developments already noted from other parts of
the world are found to occur in medieval Europe, often coming through
channels of communication more precisely determinable than those hitherto
mentioned. Before the influx of Islamic learning at the time of transmission
of the Toledo Tables (12th century) and the Alfonsine Tables (which
reached Paris ca. 1292), there are occasional references to the most
primitive mechanized "visual aids" in astronomy.
The most famous of these occurs in an historical account by Richer of
Rheims about his teacher Gerbert (born 946, later Pope Sylvester II, 990-
1003). Several instruments made by Gerbert are described in detail; he
includes a fine celestial globe made of wood covered with horsehide and
having the stars and lines painted in color, and an armillary sphere having
sighting tubes similar to those always found on Chinese instruments but
never on the Ptolemaic variety. Lastly, he cites "the construction of a
sphere, most suitable for recognizing the planets," but unfortunately it is not
clear from the description whether or not the model planets were actually to
be animated mechanically. The text runs:27

Within this oblique circle (the zodiac on the ecliptic of the globe) he hung the circles of the
wandering stars (the planets) with marvellous ingenuity, whose orbits, heights and even the distance
from each other he demonstrated to his pupils most effectually. Just how he accomplished this it is
unsuitable to enter into here because of its extent lest we should appear to be wandering from our
main theme.

Thus, although there is a hint of mechanical complexity, there is really no
justification for such an assumption; the description might well imply only
a zodiac band on which the orbits of the planets were painted. On the other
hand it is not inconceivable that Gerbert could have learned something of
Islamic and other extra-European traditions during his period of study with
the Bishop of Barcelona—a traveling scholarship that seems to have had
many repercussions on the whole field of European scholarship.
Once the floodgates of Arabic learning were opened, a stream of
mechanized astronomical models poured into Europe. Astrolabes and
equatoria rapidly became very popular, mainly through the reason for which
they had been first devised, the avoidance of tedious written computation.
Many medieval astrolabes have survived, and at least three medieval
equatoria are known. Chaucer is well known for his treatise on the

astrolabe; a manuscript in Cambridge, containing a companion treatise on
the equatorium, has been tentatively suggested by the present author as also
being the work of Chaucer and the only piece written in his own hand.
The geared astrolabe of al-Biruni is another type of protoclock to have been
transmitted. A specimen in the Science Museum, London,28 though
unfortunately now incomplete, has a very sophistocated arrangement of
gears for moving pointers to indicate the correct relative positions and
movements of the sun and moon (see figs. 17 and 18). Like the earlier
Muslim example it contains wheels with odd numbers of gear teeth (14, 27,
39); however, the teeth are no longer equilateral in shape, but approximate a
more modern slightly rounded form. This example is French and appears to
date from ca. 1300. Another Gothic astrolabe with a similar gear ring on the
rete, said to date from ca. 1400 (it could well be much earlier) is now in the
Billmeier collection (London).29
Turning from the mechanized astrolabe to the mechanized equatorium, we
find the work of Richard of Wallingford (1292?-1336) of the greatest
interest as providing an immediate precursor to that of de Dondi. He was
the son of an ingenious blacksmith, making his way to Merton College,
Oxford, then the most active and original school of astronomy in Europe,
and winning later distinction as Abbot of St. Albans. A text by him, dated
1326-27, described in detail the construction of a great equatorium, more
exact and much more elaborate than any that had gone before.30
Nevertheless it is evidently a normal manually operated device like all the
others. In addition to this instrument, Richard is said to have constructed ca.
1320, a fine planetary clock for his Abbey.31 Bale, who seems to have seen
it, regarded it as without rival in Europe, and the greatest curiosity of his
time. Unfortunately, the issue was confused by Leland, who identified it as
the Albion (i.e., all-by one), the name Richard gives to his manual
equatorium. This clock was indeed so complex that Edward III censured the
Abbot for spending so much money on it, but Richard replied that after his
death nobody would be able to make such a thing again. He is said to have
left a text describing the construction of this clock, but the absence of such
a work has led many modern writers to support Leland's identification and
suppose that the device was not a mechanical clock.

Figure 17.—French Geared Astrolabe of Trefoil Gothic Design, ca.
A.D. 1300. The gearing on the pointer is, from the center: (32)/14-45+27-
39, the last meshing with a concave annular gear of 180 teeth around the
rim of the rete of the astrolabe. A second pointer, geared to this so as to
follow the Moon, seems to be lacking. (Photo courtesy of Science
Museum. London.)

Figure 18.—Gear Train Of Pointer in figure 17. (Photo courtesy of
Science Museum, London.)

A corrective for this view is to be had from a St. Albans manuscript (now at
Gonville and Caius College, Cambridge) that described the methods for
setting out toothed wheels for an astronomical horologium designed to
show the motions of the planets. Although the manuscript copy is to be
dated ca. 1340, it clearly indicates that a geared planetary device was
known in St. Albans at an early date, and it is reasonable to suppose that
this was in fact the machine made by Richard of Wallingford. Unfortunately
the text does not appear to give any relevant information about the presence
of an escapement or any other regulatory device, nor does it mention the
source of power.32 Now a geared version of the Albion would appear to
correspond very closely indeed to the dial-work which forms the greater
part of the de Dondi clock, and for this reason we suggest now that the two
clocks were very closely related in other ways too. This, circumstantial
though it be, is evidence for thinking that the weight drive and some form
of escapement were known to Richard of Wallingford, ca. 1320. It would
narrow the gap between the clock and the protoclocks to less than half a
century, perhaps a single generation, in the interval ca. 1285-1320. In this
connection it may be of interest that Richard of Wallingford knew only the
Toledo tables corpus, that of the Alfonsine school did not arrive in England
until after his death.
There are, of course, many literary references to the water-clocks in
medieval literature. In fact most of these are from quotations which have
often been produced erroneously in the history of the mechanical clock,

thereby providing many misleading starts for that history, as noted
previously in the discussion of the horologium. There are however enough
mentions to make it certain that water clocks of some sort were in use,
especially for ecclesiastic purposes, from the end of the 12th century
onwards. Thus, Jocelin of Brakelond tells of a fire in the Abbey Church of
Bury St. Edmunds in the year 1198.33 The relics would have been destroyed
during the night, but just at the crucial moment the clock bell sounded for
matins and the master of the vestry sounded the alarm. On this "the young
men amongst us ran to get water, some to the well and others to the
clock"—probably the sole occasion on which a clock served as a fire
hydrant.
It seems probable that some of these water clocks could have been simple
drip clepsydras, with perhaps a striking arrangement added. A most
fortunate discovery by Drover has now brought to light a manuscript
illumination that shows that these water clocks, at least by ca, 1285, had
become more complex and were rather similar in appearance to the
Alfonsine mercury drum.34 The illustration (fig. 19) is from a moralized
Bible written in northern France, and accompanies the passage where King
Hezekiah is given a sign by the Lord, the sun being moved back ten steps of
the clock. The picture clearly shows the central water wheel and below it a
dog's head spout gushing water into a bucket supported by chains, with a
(weight?) cord running behind. Above the wheel is a carillon of bells, and to
one side a rosette which might be a fly or a model sun. The wheel appears
to have 15 compartments, each with a central hole (perhaps similar to that
in the Alfonsine clock) and it is supported on a square axle by a bracket, the
axle being wedged in the traditional fashion. The projections at the edge of
the wheel might be gear teeth, but more likely they are used only for
tripping the striking mechanism. If it were not for the running water spout it
would be very close to the Alfonsine model; but with this evidence it seems
impossible to arrive at a clear mechanical interpretation.
From the adjacent region there is another account of a striking water clock,
the evidence being inscriptions on slates, discovered in Villers Abbey near
Brussels;35 these may be closely dated as 1267 or 1268 and provide the
remains of a memorandum for the sacrist and his assistants in charge of the
clock.

Always set the clock, however long you may delay on [the letter "A"] afterwards you shall pour
water from the little pot (pottulo) that is there, into the reservoir (cacabum) until it reaches the
prescribed level, and you must do the same when you set [the clock] after compline so that you may
sleep soundly.

A quite different sort of evidence is to be had from the writings of Robertus
Anglicus in 1271 where one gets the impression that just at this time there
was active interest in the attempt to make a weight-driven anaphoric clock
and to regulate its motion by some unstated method so that it would keep
time with the diurnal rotation of the heavens:36

Nor it is possible for any clock to follow the judgment of astronomy with complete accuracy. Yet
clockmakers (artifices horologiorum) are trying to make a wheel (circulum) which will make one
complete revolution for every one of the equinoctial circle, but they cannot quite perfect their work.
But if they could, it would be a really accurate clock (horologium verax valde) and worth more than
an astrolabe or other astronomical instrument for reckoning the hours, if one knew how to do this
according to the method aforesaid. The method of making such a clock would be this, that a man
make a disc (circulum) of uniform weight in every part so far as could possibly be done. Then a lead
weight should be hung from the axis of that wheel (axi ipsius rote) and this weight would move that
wheel so that it would complete one revolution from sunrise to sunrise, minus as much time as about
one degree rises according to an approximately correct estimate. For from sunrise to sunrise, the
whole equinoctial rises, and about one degree more, through which degree the sun moves against the
motion of the firmament in the course of a natural day. Moreover, this could be done more accurately
if an astrolabe were constructed with a network on which the entire equinoctial circle was divided up.

Figure 19.—Manuscript Illumination of a Medieval Waterclock,
showing a partitioned wheel, a weight drive, and a carillion for striking.
From Drover (see footnote 34).

The text then continues with technical astronomical details of the slight
difference between the rate of rotation of the sun and of the fixed stars
(because of the annual rotation of the sun amongst the stars) but it gives no
indication of any regulatory device. Again it should be noted, this source
comes from France; Robertus, though of English origin, apparently being
then a lecturer either at the University of Paris or at that of Montpellier. The
date of this passage, 1271, has been taken as a terminus post quem for the
invention of the mechanical clock. In the next section we shall describe the

text of Peter Peregrinus, very close to this in place and date, which
describes just such a machine, conflating it with accounts of an armillary
sphere, perpetual motion, and the magnetic compass—so bringing all these
threads together for the first time in Europe.

Figure 20.—Arrangement for Turning a Figure Of an
Angel. It has been alleged that this drawing by Villard
represents an escapement. After Lassus (see footnote 37).

We have reserved to the last one section of evidence which may or may not
be misleading, the famous notebook of Villard (Wilars) of Honnecourt, near
Cambrai. The album, attributed to the period 1240-1251, contains many
drawings with short annotations, three of which are of special interest to our
investigations.37 These comprise a steeplelike structure labeled "cest li
masons don orologe" (this is the house of a clock), a device including a
rope, wheel and axle (fig. 20), marked "par chu fait om un angle tenir son
doit ades vers le solel" (by this means an angel is made to keep his finger
directed towards the sun), and a perpetual motion wheel which we shall
reserve for later discussion.

The clock tower, according to Drover, shows no place for a dial but
suggests the use of bells because of its open structure, suitable for letting
out the sound. Moreover, he suggests that the delicacy of the line indicates
that it was not really a full-size steeple but rather a small towerlike structure
standing only a few feet high within the church. There is, alas, nothing to
tell us about the clock it was intended to house; most probably it was a
water clock similar to that of the illustrated Bible of ca. 1285.
The drawing of the rope, wheel and axles, for turning an angel to point
towards the sun can have a simple explanation or a more complicated one.
If taken at its face value the wheel on its horizontal axis acts as a windlass
connected by the counterpoised rope to the vertical shaft which it turns,
thereby moving (by hand) the figure of an angel (not shown) fixed to the
top of this latter shaft. Such an explanation was in fact suggested by M.
Quicherat,38 who first called attention to the Villard album and pointed out
that a leaden angel existed in Chartres before the fire there in 1836. It is a
view also supported from another drawing in the album which describes an
eagle whose head is made to turn towards the deacon when he reads the
Gospel. Slight pressure on the tail of the bird causes a similar rope
mechanism to operate.

A quite different interpretation has been suggested by Frémont;39 he
believes that the wheel may have acted as a fly-wheel and the ropes and
counterpoises, turning first one way then the other acted as a sort of
mechanical escapement. Such an arrangement is however mechanically
impossible without some complicated free-wheeling device between the
drive and the escapement, and its only effect would be to oscillate the angel
rapidly rather than turn it steadily. I believe that Frémont, over-
anxious to provide a protoescapement, has done too much violence to the
facts and turned away without good reason from the more simple and
reasonable explanation. It is nevertheless still possible to adopt this simple
interpretation and yet to have the system as part of a clock. If the left-hand
counterpoise, conveniently raised higher than that on the right, is
considered as a float fitting into a clepsydra jar, instead of as a simple
weight, one would have a very suitable automatic system for turning the
angel. On this explanation, the purpose of the wheel would be merely to
provide the manual adjustment necessary to set the angel from time to time,
compensating for irremediable inaccuracies of the clepsydra.

Figure 21.—Villard's Perpetual Motion Wheel, from
Lassus (see footnote 37).

Having discussed the Villard drawings which are already cited in
horological literature, we must draw attention to the fact that this medieval
architect also gives an illustration of a perpetual motion wheel. In this case
(fig. 21) it is of the type having weights at the end of swinging arms, a type
that occurs very frequently at later dates in Europe and is also given in the
Islamic texts. We cannot, in this case, suggest that drawings of clocks and
of perpetual motion devices occur together by more than a coincidence, for
Villard seems to have been interested in most sorts of mechanical device.
But even this type of coincidence becomes somewhat striking when
repeated often enough. It seems that each early mention of "self-moving
wheels" occurs in connection with some sort of clock or mechanized
astronomical device.
Having now completed a survey of the traditions of astronomical models,
we have seen that many types of device embodying features later found in

mechanical clocks evolved through various cultures and flowed into
Europe, coming together in a burst of multifarious activity during the
second half of the 13th century, notably in the region of France. We must
now attempt to fill the residual gap, and in so doing examine the importance
of perpetual motion devices, mechanical and magnetic, in the crucial
transition from protoclock to mechanical-escapement clock.

Perpetual Motion and the Clock before de Dondi
We have already noted, more or less briefly, several instances of the use of
wheels "moving by themselves" or the use of a fluid for purposes other than
as a motive power. Chronologically arranged, these are the Indian devices
of ca. 1150 or a little earlier, as those of Riḍwān ca. 1200, that of the
Alfonsine mercury clock, ca. 1272, and the French Bible illumination of ca.
1285. This strongly suggests a steady transmission from East to West, and
on the basis of it, we now tentatively propose an additional step, a
transmission from China to India and perhaps further West, ca. 1100, and
possibly reinforced by further transmissions at later dates.
One need only assume the existence of vague traveler's tales about the
existence of the 11th-century Chinese clocks with their astronomical
models and jackwork and with their great wheel, apparently moving by
itself but using water having no external inlet or outlet. Such a stimulus,
acting as it did on a later occasion when Galileo received word of the
invention of the telescope in the Low Countries, might easily lead to the re-
invention of just such perpetual-motion wheels as we have already noted. In
many ways, once the idea has been suggested it is natural to associate such
a perpetual motion with the incessant diurnal rotation of the heavens.
Without some such stimulus however it is difficult to explain why this
association did not occur earlier, and why, once it comes there seems to be
such a chronological procession from culture to culture.
We now turn to what is undoubtedly the most curious part of this story, in
which automatically moving astronomical models and perpetual motion
wheels are linked with the earliest texts on magnetism and the magnetic
compass, another subject with a singularly troubled historical origin. The
key text in this is the famous Epistle on the magnet, written by Peter

Peregrinus, a Picard, in an army camp at the Siege of Lucera and dated
August 8, 1269.40 In spite of the precise dating it is certain that the work
was done long before, for it is quoted unmistakably by Roger Bacon in at
least three places, one of which must have been written before ca. 1250.41
The Epistle contains two parts; in the first there is a general account of
magnetism and the properties of the loadstone, closing with a discussion "of
the inquiry whence the magnet receives the natural virtue which it has."
Peter attributed this virtue to a sympathy with the heavens, proposing to
prove his point by the construction of a "terrella," a uniform sphere of
loadstone which is to be carefully balanced and mounted in the manner of
an armillary sphere, with its axis directed along the polar axis of the diurnal
rotation. He then continues:

Now if the stone then move according to the motion of the heavens, rejoice that you have arrived at a
secret marvel. But if not, let it be ascribed rather to your own want of skill than to a defect of Nature.
But in this position, or mode of placing, I deem the virtues of this stone to be properly conserved, and
I believe that in other positions or parts of the sky its virtue is dulled, rather than preserved. By
means of this instrument at all events you will be relieved from every kind of clock (horologium), for
by it you will be able to know the Ascendant at whatever hour you will, and all other dispositions of
the heavens which Astrologers seek after.

It should be noted that the device is to be mounted like an astronomical
instrument and used like one, rather than as a time teller, or as a simple
demonstration of magnetism. In the second part of the Epistle Peter turns to
practical instruments, describing for the first time, the construction of a
magnetic compass consisting of a loadstone or iron needle pivoted with a
casing marked with a scale of degrees. The third chapter of this section,
concluding the Epistle, then continues with the description of a perpetual
motion wheel, "elaboured with marvellous ingenuity, in the pursuit of
which invention I have seen many people wandering about, and wearied
with manifold toil. For they did not observe that they could arrive at the
mastery of this by means of the virtue, or power of this stone."

This tells us incidentally, that the perpetual motion device was a subject of
considerable interest at this time.42 Oddly enough, Peter does not now
develop his idea of the terrella, but proceeds to something quite new, a
device (see fig. 22) in which a bar-magnet loadstone is to be set towards the
end of a pivoted radial arm with a circle fitted on the inside with iron "gear

teeth," the teeth being there not to mesh with others but to draw the magnet
from one to the next, a little bead providing a counterweight to help the
inertia of rotation carry the magnet from one point of attraction to the next.
It is by no means the sort of device that one would naturally evolve as a
means of making magnetism work perpetually, and I suggest that the
toothed wheel is another instance of some vague idea of protoclocks,
perhaps that of Su Sung, being transmitted from the East.

Figure 22.—Magnetic Perpetual Motion Wheel
illustrated by Peter Peregrinus; from the edition of S. P.
Thompson (see footnote 40).

The work of Peter Peregrinus is cited by Roger Bacon in his De secretis as
well as in the Opus majus and Opus minus. In the first and earliest of these
occurs a description, taken from Ptolemy, of the construction of the
(observing) armillary sphere. He says that this cannot be made to move
naturally by any mathematical device, but "a faithful and magnificent
experimentor is straining to make one out of such material, and by such a
device, that it will revolve naturally with the diurnal heavenly rotation." He
continues with the statement that this possibility is also suggested by the

fact that the motions of comets, of tides, and of certain planets also follow
that of the Sun and of the heavens. Only in the Opus minus, where he
repeats reference to this device, does he finally reveal that it is to be made
to work by means of the loadstone.
The form of Bacon's reference to Peregrinus is strongly reminiscent of the
statement by Robertus Anglicus, already mentioned as an indication of
preoccupation with diurnally rotating wheels, at a date (1271) remarkably
close to that of the Epistle (1269)—so much so that it could well be thought
that the friend to which Peter was writing was either Robert himself or
somebody associated with him, perhaps at the University of Paris—a
natural place to which the itinerant Peter might communicate his findings.
The fundamental question here, of course, is whether the idea of an
automatic astronomical device was transmitted from Arabic, Indian, or
Chinese sources, or whether it arose quite independently in this case as a
natural concomitant of identifying the poles of the magnet with the poles of
the heavens. We shall now attempt to show that the history of the magnetic
compass might provide a quite independent argument in favour of the
hypothesis that there was a 'stimulus' transmission.

The Magnetic Compass as a Fellow-traveler from China
The elusive history of the magnetic compass has many points in common
with that of the mechanical clock. Just as we have astronomical models
from the earliest times, so we find knowledge of the loadstone and some of
its properties. Then, parallel to the development of protoclocks in China
throughout the middle ages, we have the evidence analyzed by Needham,
showing the use of the magnet as a divinatory device and of the
(nonmagnetic) south-pointing chariot, which has been confusedly allied to
the story. Curiously, and perhaps significantly the Chinese history comes to
a head at just the same time for compasses and clocks, and a prime
authority for the Chinese compass is Shen Kua (1030-1093) who also
appears in connection with the clock of Su Sung, and who wrote about the
mechanized armillary spheres and other models ca. 1086.
Another similarity occurs in connection with the history of the compass in
medieval Europe. The treatise of Peter Peregrinus, already discussed,

provides the first complete account of the magnetic compass with a pivoted
needle and a circular scale, and this, as we have seen, may be connected
with protoclocks and perpetual-motion devices. There are several earlier
references, however, to the use of the directive properties of loadstone,
mainly for use in navigation, but these earliest texts have a long history of
erroneous interpretation which is only recently being cleared away. We
know now that the famous passages in the De naturis rerum and De
utensilibus of Alexander Neckham43 (ca. 1187) and a text by Hugues de
Berze44 (after ca. 1204) refer to nothing more than a floating magnet
without pivot or scale, but using a pointer at right angles to the magnet, so
that it pointed to the east, rather than the north or south. A similar method is
described (ca. 1200) in a poem by Guyot de Provins, and in a history of
Jerusalem by Jacques de Vitry (1215).45 It is of the greatest interest that,
once more, all the evidence seems to be concentrated in France (Neckham
was teaching in Paris) though at an earlier period than that for the
protoclocks.
The date might suggest the time of the first great wave of transmissal of
learning from Islam, but it is clear that in this instance, peculiar for that
reason, that Islam learned of the magnetic compass only after it was already
known in the West. In the earliest Persian record, some anecdotes compiled
by al-'Awfiī ca. 1230,46 the instrument used by the captain during a storm at
sea has the form of a piece of hollow iron, shaped like a fish and made to
float on the water after magnetization by rubbing with a loadstone; the
fishlike form is very significant, for this is distinctly Chinese practice. In a
second Muslim reference, that of Bailak al-Qabājaqī (ca. 1282), the
ordinary wet-compass is termed "al-konbas," another indication that it was
foreign to that language and culture.47

Chronological Chart

China
4th C., B.C. Power gearing

Classical Europe
3rd C., B.C. Archimedes planetarium
2nd C., B.C. Hipparchus Stereographic Projection
1st C., B.C. Vitruvius hodometer and water clocks
65, B.C. (ca.) Antikythera machine
1st C., A.D. Hero hodometer and water clocks
2nd C., A.D. Salzburg and Vosges anaphoric clocks

China
2nd C., A.D. Chang Hêng animated globe hodometer
Continuing tradition of animated astronomical models
725 Invention of Chinese escapement by I-Hsing and Liang Ling-tsan

Islam
807 Harun-al-Rashid
850 (ca.) Earliest extant astrolobes
1000 Geared astrolabe of Buruni

Europe
1000 Gerbert astronomical model

Islam
1025 Equatorium text

China
1074 Shen Kua, clocks and magnetic compass
1080 Su Sung clock built
1101 Su Sung clock destroyed

India
1100 (ca.) Sūrya Siddhānta animated astronomical models and perpetual motion
1150 (ca.) Siddhānta Siromaṇi animated models and perpetual motion

Islam
1150 Saladin clock

Europe
1187 Neckham on compass
1198 Jocelin on water clock

Islam
1200 (ca.) Riḍwān water-clocks, perpetual motion and weight drive
1206 al-Jazarī clocks, etc.
1221 Geared astrolabe
1232 Charlemagne clock
1243 al-Konbas (compass)

Europe
1245 Villard clocktower, "escapement," perpetual motion
1267 Villers Abbey clock
1269 Peregrinus, compass and perpetual motion
1271 Robertus Anglicus, animated models and "perpetual motion" clock

Islam
1272 Alfonsine corpus clock with mercury drum, equatoria

Europe
1285 Drover's water clock with wheel and weight drive
1300 (ca.) French geared astrolabe
1320 Richard of Wallingford astronomical clock and equatorium
1364 de Dondi's astronomical clock with mechanical escapement
later 14th C. Tradition of escapement clocks continues and degenerates into simple time-keepers

There is therefore reasonable grounds for supporting the medieval European
tradition that the magnetic compass had first come from China, though one
cannot well admit that the first news of it was brought, as the legend states,
by Marco Polo, when he returned home in 1260. There might well have
been another wave of interest, giving the impetus to Peter Peregrinus at this
time, but an earlier transmission, perhaps along the silk road or by travelers
in crusades, must be postulated to account for the evidence in Europe, ca.
1200. The earlier influx does not play any great part in our main story; it
arrived in Europe before the transmission of astronomy from Islam had got
under way sufficiently to make protoclocks a subject of interest. For a
second transmission, we have already seen how the relevant texts seem to
cluster, in France ca. 1270, around a complex in which the protoclocks
seem combined with the ideas of perpetual motion wheels and with new
information about the magnetic compass.
The point of this paper is that such a complex exists, cutting across the
histories of the clock, the various types of astronomical machines, and the
magnetic compass, and including the origin of "self-moving wheels." It
seems to trace a path extending from China, through India and through
Eastern and Western Islam, ending in Europe in the Middle Ages. This path
is not a simple one, for the various elements make their appearances in
different combinations from place to place, sometimes one may be
dominant, sometimes another may be absent. Only by treating it as a whole
has it been possible to produce the threads of continuity which will, I hope,
make further research possible, circumventing the blind alleys found in the
past and leading eventually to a complete understanding of the first
complicated scientific machines.

FOOTNOTES:
1 This traditional view is expressed by almost every history of horology. An ultimate
source for many of these has been the following two classic treatments: J. Beckmann,
A history of inventions and discoveries, 4th ed., London, 1846, vol. 1, pp. 340 ff. A. P.
Usher, A history of mechanical inventions, 2nd ed., Harvard University Press. 1954,
pp. 191 ff., 304 ff.
2 There is a considerable literature dealing with the later evolution of perpetual
motion devices. The most comprehensive treatment is H. Dircks, Perpetuum mobile,
London, 1861; 2nd ser., London, 1870. So far as I know there has not previously been
much discussion of the history of such devices before the renaissance.

3 For the early history of gearing in the West see C. Matschoss, Geschichte des
Zahnrades, Berlin, 1940. Also F. M. Feldhaus, Die geschichtliche Entwicklung des
Zahnrades in Theorie und Praxis, Berlin, 1911.
4 A general account of these important archaeological objects will be published by J.
Needham, Science and civilisation in China, Cambridge, 1959(?), vol. 4. The original
publications (in Chinese) are as follows: Wang Chen-to, "Investigations and
reproduction in model form of the south-pointing carriage and hodometer," National
Peiping Academy Historical Journal, 1937, vol. 3, p. 1. Liu Hsien-chou, "Chinese
inventions in horological engineering," Ch'ing-Hua University Engineering Journal,
1956, vol. 4, p. 1.
5 For illustrations of intermeshing worms in Indian cotton mills, see Matschoss, op.
cit. (footnote 3), figs. 5, 6, 7, p. 7.
6 It is interesting to note that the Chinese hodometer was contemporary with that of
Hero and Vitruvius and very similar in design. There is no evidence whatsoever upon
which to decide whether there may have been a specific transmission of this invention
or even a "stimulus diffusion."
7 A summary of the content of the manuscript sources, illustrated by the original
drawings, has been published by H. Alan Lloyd, Giovanni de Dondi's horological
masterpiece, 1364, without date or imprint (?Lausanne, 1955), 23 pp. It should be
remarked that de Dondi declines to describe the workings of his crown and foliot
escapement (though it is well illustrated) saying that this is of the "common" variety
and if the reader does not understand such simple things he need not hope to
comprehend the complexities of this mighty clock. But this may be bravado to quite a
large degree.
8 See, for example, the chronological tables of the 14th century and the later mentions
of clocks in E. Zinner, Aus der Frühzeit der Räderuhr, Munich, 1954, p.
29 ff. Unfortunately this very complete treatment tends to confuse the factual and
legendary sources prior to the clock of de Dondi; it also accepts the very doubtful
evidence of the "escapement" drawn by Villard of Honnecourt (see p. 107). An
excellent and fully illustrated account of monumental astronomical clocks throughout
the world is given by Alfred Ungerer, Les horloges astronomiques, Strasbourg, 1931,
514 pp. Available accounts of the development of the planetarium since the middle
ages are very brief and especially weak on the early history: Helmut Werner, From the
Aratus globe to the Zeiss planetarium, Stuttgart, 1957; C. A. Crommelin, "Planetaria,
a historical survey," Antiquarian Horology, 1955, vol. 1, pp. 70-75.
9 Derek J. Price, "Clockwork before the clock," Horological Journal, 1955, vol. 97, p.
810, and 1956, vol. 98, p. 31.
10 For the use of this material I am indebted to my co-authors. I must also
acknowledge thanks to the Cambridge University Press, which in the near future will
be publishing our monograph, "Heavenly Clockwork." Some of the findings of this
paper are included in shorter form as background material for that monograph. A brief
account of the discovery of this material has been published by J. Needham, Wang
Ling, and Derek J. Price, "Chinese astronomical clockwork," Nature, 1956, vol. 177,
pp. 600-602.

11 For these translations from classical authors I am indebted to Professor Loren
MacKinney and Miss Harriet Lattin, who had collected them for a history, now
abandoned, of planetariums. I am grateful for the opportunity of giving them here the
mention they deserve.
12 A. G. Drachmann, "The plane astrolabe and the anaphoric clock," Centaurus,
1954, vol. 3, pp. 183-189.
13 A fuller description of the anaphoric clock and cognate water-clocks is given by A.
G. Drachmann, "Ktesibios, Philon and Heron," Acta Historica Scientiarum
Naturalium et Medicinalium, Copenhagen, 1948, vol. 4.
14 First published by O. Benndorf, E. Weiss, and A. Rehm, Jahreshefte des
österreichischen archäologischen Institut in Wien, 1903, vol. 6, pp. 32-
49. I have given further details of its construction in A history of technology, ed.
Singer, Holmyard, and Hall, 1957, vol. 3, pp. 604-605.
15 L. Maxe-Werly, Mémoires de la Société Nationale des
Antiquaires de France, 1887, vol. 48, pp. 170-178.
16 The first definitive account of the Antikythera machine was given by Perikles
Rediadis in J. Svoronos, Das Athener Nationalmuseum, Athens, 1908, Textband I, pp.
43-51. Since then, other photographs (mostly very poor) have appeared, and an
attempt at a reconstruction has been made by Rear Admiral Jean Theophanidis,
Praktika tes Akademias Athenon, Athens, 1934, vol. 9, pp. 140-149 (in French). I am
deeply grateful to the Director of the Athens National Museum, M. Karouzos, for
providing me with an excellent new set of photos, from which figures 6-8 are now
taken.
17 H. Diels Über die von Prokop beschriebene Kunstuhr von Gaza,
Abhandlungen, Akademie der Wissenschaften, Berlin, Philos.-Hist. Klasse, 1917, No.
7.
18 L. A. Mayer, Islamic astrolabists and their works, Geneva, 1956, p. 62.
19 The translation which follows is quoted from J. Beckmann, op. cit. (footnote 1), p.
349.
20 E. Wiedemann, "Ein Instrument das die Bewegung von Sonne und Mond darstellt,
nach al Biruni," Der Islam, 1913, vol. 4, p. 5.
21 I acknowledge with thanks to the Curator of that museum the permission to
reproduce photographs of this instrument. It is item 5 in R. T. Gunther, Astrolabes of
the world, Oxford, 1932.
22 Abulcacim Abnacahm, Libros del saber, edition by Rico y Sinobas, Madrid, 1866,
vol. 3, pp. 241-271. The design of the instrument has been very fully discussed by A.
Wegener, "Die astronomischen Werke Alfons X," Bibliotheca Mathematica, 1905, pp.
129-189. A more complete discussion of the historical evolution of the equatorium is
given in Derek J. Price, The equatorie of the planetis, Cambridge (Eng.), 1955, pp.
119-133.
23 E. Wiedemann, and F. Hauser, "Uber die Uhren im Bereich d. islamischen Kultur,"
Nova Acta; Abhandlungen der königliche Leopoldinisch-Carolinische Deutsche

Akademie der Naturforscher zu Halle, 1915, vol. 100, no. 5.
24 E. Wiedemann, and F. Hauser, Die Uhr des Archimedes und zwei andere
Vorrichtungen, Halle, 1918.
25 The manuscripts in question are as follows: Gotha, Kat. v. Pertsch. 3, 18, no. 1348;
Oxford, Cod. 954; Leiden, Kat. 3, 288, no. 1414, Cod. 499 Warn; and another similar,
Kat. 3, 291, no. 1415, Cod. 93 Gol.
26 H. Schmeller, Beiträge zur Geschichte der Technik in der Antike und bei den
Arabern, Erlangen, 1922 (Abhandlungen zur Geschichte der Naturwissenschaften und
der Medizin no. 6).
27 Once more I am indebted to Professor Loren MacKinney and Miss Harriet Lattin
(see footnote 11) for making their collections on Gerbert available to me.
28 Item 198 in Gunther, op. cit. (footnote 21). I am grateful to the authorities of that
museum for permission to reproduce photographs of this instrument.
29 Sotheby and Co., London, sale of March 14, 1957, lot 154. The outer rim of the
rete has 120 teeth.
30 The Latin text of the treatise on the Albion, has been transcribed by Rev. H. Salter
and published in R. T. Gunther, Early science in Oxford, Oxford, 1923, vol. 2, pp.
349-370. An analysis of its design is given in Price, op. cit. (footnote 22), pp. 127-
130.
31 Such evidence as there is for the existence and form of the clock is collected by
Gunther, op. cit. (footnote 30), p. 49.
32 I have discussed this new manuscript source in "Two medieval texts on
astronomical clocks," Antiquarian Horology, 1956, vol. 1, no. 10, p. 156. The
manuscript in question is ms. 230/116, Gonville and Caius College, Cambridge, folios
11v-14v = pp. 31-36.
33 The Chronicle of Jocelin of Brakelond ..., H. E. Butler (ed.), London, 1949, p. 106.
34 C. B. Drover, "A medieval monastic water-clock," Antiquarian Horology, 1954,
vol. 1, no. 5, pp. 54-58, 63. Because this water clock uses wheels and strikes bells one
must reject the evidence of literary reference, such as by Dante, from which the
mention of wheels and bells have been taken as positive proof of the existence of
mechanical clocks with mechanical escapements. The to-and-fro motion of the
mechanical clock escapement is quite an impressive feature, but there seems to be no
literary reference to it before the time of de Dondi.
35 Annales de la Société Royale d'Archéologie de Bruxelles,
1896, vol. 1/8, pp. 203-215, 404-451. The translation here is cited from Drover, op.
cit., (footnote 34), p. 56.
36 L. Thorndike, The sphere of Sacrobosco and its commentators, Chicago, 1949, pp.
180, 230.
37 The album was published with facsimiles by J. B. A. Lassus, 1858. An English
edition with facsimiles of 33 of the 41 folios was published by Rev. Robert Willis,

Oxford, 1859. An extensive summary of this section is given, with illustrations, by J.
Drummond Robertson, The evolution of clockwork, London, 1931, pp. 11-15.
38 M. Jules Quicherat, Revue Archèologique, 1849, vol. 6.
39 M. C. Frémont. Origine de l'horloge à poids, Paris, 1915.
40 For this, I have used and quoted from the very beautiful edition in English,
prepared by Silvanus P. Thompson, London, Chiswick Press, 1902.
41 See E. G. R. Taylor, "The South-pointing needle," Imago Mundi, Leiden, 1951,
vol. 8, pp. 1-7 (especially pp. 1, 2).
42 I have wondered whether the medieval interest in perpetual motion could be
connected with the use of the "Wheel of Fortune" in churches as a substitute for bell-
ringing on Good Friday. Unfortunately I can find no evidence for or against the
conjecture.
43 W. E. May, "Alexander Neckham and the pivoted compass needle," Journal of the
Institute of Navigation, 1955, vol. 8, no. 3, pp. 283-284.
44 W. E. May, "Hugues de Berze and the mariner's compass," The Mariner's Mirror,
1953, vol. 39, no. 2, pp. 103-106.
45 H. Balmer, Beiträge zur Geschichte der Erkenntnis des Erdmagnetismus,
Aarau, 1956, p. 52.
46 The collection is the Gami 'al Hikajat; the relevant passage being given in German
translation in Balmer. op. cit. (footnote 45), p. 54.
47 Balmer, op. cit. (footnote 45), p. 53.

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