81

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

82

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

By Derek J. de Solla Price

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has too often been replaced by conjecture, and conjecture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
83necessary 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
84B.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 me85chanical 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.

86

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
87stars. 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 for88
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.

89

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):

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

90

A similar arrangement seems to be indicated in
another mechanized globe, also mentioned by Cicero
and said to have been made by Posidonius:

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:

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

91

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-92keeping 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 graduated93
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 the94
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.

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 mentioned95
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

96

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
97
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

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
98explains 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.

99

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
100much 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 anaphoric101 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 Wheel, after manuscript cited by Schmeller (see footnote 26).

Figure 15.—Another Perpetual Motion Wheel, after the text cited in figure 14.

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
102

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

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.

104

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

105

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.

106

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.

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

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.

107

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,
108turning 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

109

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:

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
110and 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

111

Chronological Chart

112

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:

U.S. GOVERNMENT PRINTING OFFICE: 1959