----------------------------------------
----------------------      ,this e-text
 includes characters that require       
,,utf-#h                7,unicode7 file 
encoding3                               
1 1 1 1                                 
,if any of these characters do not      
display properly--in                    
particular1 if the dots do not appear   
under the letters           make sure   
your text reader's 8character set0 or   
8file             encoding0 is set to   
,unicode 7,,utf-#h74 ,you may also need 
to         change the default font4     
,depending on available fonts1 some     
tables may not line up vertically4      
----------------------------------------
----------------------                  
,,contributions ,,from      ,,the       
,,museum ,,of ,,history ,,and           
,,technology3      ,,paper #f           
,,on ,,the ,,origin ,,of ,,clockwork1   
,,perpetual ,,motion ,,devices ,,and    
,,the ,,compass      ,derek ,j4 de      
,solla ,price          ,,power ,,and    

,,motion ,,gearing                      
#hc      ,,mechanical ,,clocks          
#hd      ,,mechanized ,,astronomical    
,,models                             #hh
      ,,perpetual ,,motion ,,and ,,the  
,,clock ,,before ,,de ,,dondi           
#ajh      ,,the ,,magnetic ,,compass    
,,as ,a ,,fellow-,,traveler ,,from      
,,china      #aaj            ,,on ,,the 
,,origin ,,of ,,clockwork1              
,,perpetual ,,motion ,,devices          
,,and ,,the ,,compass      ,by ,derek   
,j4 de ,solla ,price      ,ancestor of  
the mechanical clock has been thought by
 some to be the  sundial4 ,actually     
these devices represent two different   
approaches to  the problem of           
time-keeping4 ,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 bodies4    ,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  #b1jjj years of  
history on three continents4    ,,the   
,,author3 ,derek ,j4 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
 ,museum4      ,in each successive age  
this construction1 having become        
lost1 is1 by the ,sun's favour1 again   
revealed to some one    or other at his 
pleasure4 7,srya ,siddhnta1 ed4         
,burgess1 xiii1 #ah-ai47      ,,the     
,,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 inventions4 ,ignorance  
has too often been  replaced by         
conjecture1 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 next4

 ,in  what follows1 ,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 ideas4    
,for the mechanical clock1 perhaps the  
greatest hindrance has been its         
treatment within a self-contained       
history of time measurement in which    
sundials1 water-clocks and similar      
devices assume the natural role of      
ancestors to the weight-driven          
escapement clock in the early #adth     
century4#a ,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 ingenuities4       
,furthermore1 even if one admits the use
 of clocklike gearing before the        
existence of the clock1 it is still     

necessary to look for the  independent  
inventions of the weight-drive and of   
the mechanical  escapement4 ,the first  
of these may seem comparatively trivial2
 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 power4    
,nevertheless1 the use of this  device  
is not recorded before its association  
with hydraulic and  perpetual motion    
machines in the manuscripts of ,riwn1   
ca4 #abjj1  and its use in a clock using
 such a perpetual motion wheel 7mercury 
filled7 as a clock escapement1 in the   
astronomical codices of ,alfonso  the   
,wise1 ,king of ,castile1 ca4 #abgb4    
,the second invention1 that of the      
mechanical escapement1 has presented    
one of the most tantalizing of problems4
 ,without doubt1 the crown and  foliot  
type of escapement appears to be the    
first complicated mechanical  invention 
known to the ,european ,middle ,ages2 it

 heralds our whole age of               
machine-making4 ,yet no trace has been  
found either of a steady evolution  of  
such escapements or of their invention  
in ,europe1 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 clocks4 ,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 machines4 ,after this we   
shall for the first time  present       
evidence to show that this story is     
curiously related to that of  the       
,perpetuum ,mobile1 one of the great    
chimeras of science1 that came  from its
 medieval origin to play an important   
part in more recent  developments of    
energetics and the foundations of       
thermodynamics4#b ,it  is a curious     
mixture1 all the more so because1       

tangled inextricably in  it1 we shall   
find the most important and earliest    
references to the use  of the magnetic  
compass in the ,west4 ,it seems that in 
revising the  histories of clockwork and
 the magnetic compass1 these            
considerations  of perpetual motion     
devices may provide some much needed    
evidence4    ,illustration3 ,figure     
#a4--;,,framework ,,structure ,,of ,,the
 ,,astronomical ,,clock  of ,giovanni de
 ,dondi of ,padua1 ,a4,d4 #acfd4        
,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 era4        
,certainly1 in classical times  they    
were already familiar to ,archimedes    
7born #bhg ,b4,c471#c and in  ,china    
actual examples of wheels and moulds for
 wheels dating from the  #dth century   
,b4,c4 have been preserved4#d ,it might 
be remarked that  these machine gear    

wheels are characterized by having a    
round number  of teeth 7examples with   
#af1 #bd and #dj teeth are known7 and a 
shank with  a square hole which fits    
without turning on a squared shaft4     
,another  remarkable feature in these   
early gears is the use of ratchet-shaped
  teeth1 sometimes even twisted         
helically so that the gears resemble    
worms  intermeshing on parallel axles4#e
 ,the existence of windmills and        
watermills testifies to the general     
familiarity1 from classical times  and  
through the middle ages1 with the use of
 gears to turn power through  a right   
angle4    ,illustration3 ,figure        
#b4--;,,astronomical ,,clock of de      
,dondi1 showing  gearing on the dial for
 ,mercury and escapement crown wheel4   
,each of the  seven side walls of the   
structure shown in figure #a was fitted 
with a  dial4    ,granted1 then1 this   
use of gears1 one must guard against any
 conclusion  that the fine-mechanical   
use of gears to provide special ratios  

of  angular movement was similarly      
general and widespread4 ,it is customary
  to adduce here the evidence of the    
hodometer 7taximeter7 described by      
,vitruvius 7#ast century ,b4,c47 and by 
,hero of ,alexandria 7#ast century      
,a4,d47 and the ingenious automata also 
described by this latter author  and his
 ,islamic followers4#f ,one may also    
cite the use of the reduction  gear     
chain in power machinery as used in the 
geared windlass of  ,archimedes and     
,hero4    ,unfortunately1 even the most 
complex automata described by ,hero and 
by  such authors as ,riwn contain       
gearing in no more extensive context    
than as a means of transmitting action  
around a right angle4 ,as for the       
windlass and hodometer1 they do1 it is  
true1 contain whole series of  gears    
used in steps as a reduction mechanism1 
usually for an  extraordinarily high    
ratio1 but here the technical details   
are so  etherial that one must doubt    
whether such devices were actually      

realized  in practice4 ,thus ,vitruvius 
writes of a wheel #d feet in diameter   
and  having #djj teeth being turned by a
 #a-toothed pinion on a cart axle1 but  
it is very doubtful whether such small  
teeth1 necessarily separated by  about  
#c_/h inch1 would have the requisite    
ruggedness4 ,again1 ,hero  mentions a   
wheel of #cj teeth which1 because of    
imperfections1 might need  only #bj     
turns of a single helix worm to turn it6
 ,such statements behove  caution and   
one must consider whether we have been  
misled by the  #afth- and #agth-century 
editions of these authors1 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 mechanism4 ,at all 
events1 even if one  admits without     
substantial evidence that such gear     
reduction devices  were familiar from   
,hellenistic times onwards1 they can    
hardly serve as  more than very distant 

ancestors of the earliest mechanical    
clocks4          ,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  gap4   
,recent research on the history of early
 mechanical clocks has  demonstrated    
certain peculiarities most relevant to  
our present  argument4      ,,the       
,,european ,,tradition    ,if one is to 
establish a terminus ante quem for the  
appearance of the  mechanical clock in  
,europe1 it would appear that #acfd is a
 most  reasonable date4 ,at that time we
 have the very full mechanical and      
historical material concerning the      
horological masterpiece built by        
,giovanni de ,dondi of ,padua1#g and    
probably started as early as #acdh4 ,it 
might well be possible to set a date a  
few decades earlier1 but in  general as 
one proceeds backwards from this point1 

the evidence becomes  increasingly      
fragmentary and uncertain4 ,the greatest
 source of doubt  arises from the       
confusion between sundials1             
water-clocks1 hand-struck  time bells1  
and mechanical clocks1 all of which are 
covered by the term  horologium and its 
vernacular equivalents4    ,temporarily 
postponing the consideration of evidence
 prior to ca4  #acej1 we may take       
,giovanni de ,dondi as a starting point 
and trace a  virtually unbroken lineage 
from his time to the present day4 ,one  
may  follow the spread of clocks through
 ,europe1 from large towns to small     
ones1 from the richer cathedrals and    
abbeys to the less wealthy  churches4#h 
,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       
watches4 ,in mechanical refinement a    
similar continuity  may be noted1 so    

that one sees the cumulative effect of  
the introduction  of the spring drive   
7ca4 #adge71 pendulum control 7ca4      
#afej71 and the  anchor escapement 7ca4 
#afhj74 ,the transition from de ,dondi  
to the  modern chronometer is indeed    
basically continuous1 and though much   
research needs to be done on special    
topics1 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 technology4           
,illustration3 ,figure #c4--;,,german   
,,wall ,,clock1 ,,probably ,,about      
#adej1  showing the degeneration in     
complexity from that of de ,dondi's     
clock4    ,most remarkable however is   
the earliest period of this seemingly   
steady  evolution4 ,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
 devolution4 ,not only is de  ,dondi's  

the earliest clock of which we have a   
full and trustworthy  account1 it is    
also far more complicated than any other
 7see figs4 #a1 #b7  until comparatively
 modern times6 ,moreover1 it was not an 
exceptional  freak4 ,there were others  
like it1 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 ,europe4    ,on the 
basis of such evidence ,i have suggested
 elsewhere#i that the  clock is nought  
but a fallen angel from the world of    
astronomy4 ,the  first great clocks of  
medieval ,europe were designed as       
astronomical  showpieces1 full of       
complicated gearing and dials to show   
the motions of  the ,sun1 ,moon and     
planets1 to exhibit eclipses1 and to    
carry through the  involved computations
 of the ecclesiastical calendar4 ,as    
such they were  comparable to the       
orreries of the #ahth century and to    
modern  planetariums2 that they also    

showed the time and rang it on bells was
  almost incidental to their main       
function4 ,one must not neglect1 too1   
that it was in their glorification of   
the rationality of the cosmos that  they
 had their greatest effect4 ,through    
milleniums of civilization1  man's      
understanding of celestial phenomena had
 been the very pinnacle of  his         
intellect1 and then as now popular      
exhibition of this sort was just  as    
necessary1 as striking1 and as          
impressive4 ,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       
,dante4    ,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 sundials1 sand glasses and the  
elementary water clocks4  ,rather it    
should be considered as a degenerate    
branch from the main stem  of mechanized

 astronomical devices 7,i shall call    
them protoclocks71 a  stem which can    
boast a continuous history filling the  
gap between the  appearance of simple   
gearing and the complications of de     
,dondi4 ,we shall  return to the        
discussion of this main stem after      
analyzing the very  recently discovered 
parallel stem from medieval ,china1     
which reproduced  the same evolution of 
mechanized astronomical devices and     
incidental  time telling4 ,of the       
greatest significance1 this stem reveals
 the  crucial independent invention of a
 mechanical escapement1 a feature not   
found in the ,european stem in spite of 
centuries of intensive historical       
research and effort4      ,,the         
,,chinese ,,tradition    ,for this      
section ,i am privileged to draw upon a 
thrilling research  project carried out 
in #aief at the ,university of          
,cambridge by a team  consisting of ,dr4
 ,joseph ,needham1 ,dr4 ,wang ,ling1 and
 myself4#aj ,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  and1 though well known 
in ,china1 had not been recognized as   
important  for their horological        
content4 ,the key text with which we    
started was  the ,hsin ,i ,hsiang ,fa   
,yao1 or ,new ,design for a 7mechanized7
 ,armillary  7sphere7 and 7celestial7   
,globe1 written by ,su ,sung in ,a4,d4  
#ajij4 ,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 similar1 though less    
extensive texts1 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-tsan1 in ,a4,d4 #gbe1 and to what 
seems to be the original of  all these  
,chinese astronomical machines1 that    
built by ,chang ,hng ca4  ,a4,d4 #acj4  

,filling the gaps between these         
landmarks are several other  similar    
texts1 giving ample evidence that the   
,chinese development is  continuous and1
 at least from ,chang ,hng onwards1     
largely independent of  any             
transmissions from the ,west4    ,so far
 as we can see1 the beginning of the    
chain in ,china 7as indeed in  the      
,west7 was the making of simple static  
models of the celestial  sphere4 ,an    
armillary sphere was used to represent  
the chief imaginary  circles 7e4g41     
equator1 ecliptic1 meridians1 etc471 or 
a solid  celestial globe on which such  
circles could be drawn1 together with   
the  constellations of the fixed stars4 
,the whole apparatus was then mounted   
so that it was free to revolve about its
 polar axis and another ring or  a      
casing was added1 external and fixed1 to
 represent the horizon that  provided a 
datum for the rising and setting of the 
,sun and the stars4    ,in the next     
stage1 reached very soon after this1 the

 rotation of the  model was arranged to 
proceed automatically instead of by     
hand4 ,this was  done1 we believe1 by   
using a slowly revolving wheel powered  
by dripping  water and turning the model
 through a reduction mechanism1 probably
  involving gears or1 more reasonably1 a
 single large gear turned by a  trip    
lever4 ,it did not matter much that the 
time-keeping properties were  poor in   
the long run2 the model moved by itself 
and the great wonder  was that it agreed
 with the observed heavens like the two 
halves of a  tally4    ,in the next1 and
 essential1 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 check1 scoop
 by  scoop1 while each scoop was filled 
by the dripping water1 then released  by
 the weighbridge and allowed to rotate  
until checked again by the  trip-lever  
arrangement4 ,its action was similar to 
that of the anchor  escapement1 though  

its period of repose was much longer    
than its period  of motion and1 of      
course1 its time-keeping properties were
 controlled not  only by the mechanics  
of the device but also by the rate of   
flow of the  dripping water4    ,the    
,chinese escapement may justifiably be  
regarded as a missing link1  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 action1 repeated indefinitely 
and counted by a  cumulating device4    
,with its characteristic of saving up   
energy for a  considerable period 7about
 #ae minutes7 before letting it go in   
one  powerful action1 the ,chinese      
escapement was particularly suited to   
the  driving of jackwork and other      
demonstration devices requiring much    
energy but only intermittent activity4  
,in its final form1 as built by ,su     
,sung after many trials and             
improvements1 the ,chinese astronomical 

clock-tower must have been a  most      
impressive object4 ,it had the form of a
 tower about #cj feet high1  surmounted 
by an observation platform covered with 
a light roof 7see  fig4 #d74 ,on the    
platform was an armillary sphere        
designed for observing  the heavens4 ,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  used4 ,below the      
platform was an enclosed chamber        
containing the  automatically rotated   
celestial globe which so wonderfully    
agreed with  the heavens4 ,below this1  
on the front of the tower was a         
miniature  pagoda with five tiers2 on   
each tier was a doorway through which1  
at due  moment1 appeared jacks who rang 
bells1 clanged gongs1 beat drums1 and   
held tablets to announce the arrival of 
each hour1 each quarter 7they  used #ajj
 of them to the day7 and each watch of  

the night4 ,within the  tower was       
concealed the mechanism2 it consisted   
mainly of a central  vertical shaft     
providing power for the sphere1 globe1  
and jackwheels1  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 
quarter4 ,in addition to all this were  
the levers of the escapement  mechanism 
and a pair of norias by which1 once each
 day1 the water used  was pumped from a 
sump at the bottom to a reservoir at the
 top1 whence  it descended to work the  
wheel by means of a constant level tank 
and  several channels4    ,there were   
many offshoots and developments of this 
main stem of ,chinese  horology4 ,we are
 told1 for example1 that often mercury  
and occasionally  sand were used to     
replace the water1 which frequently     
froze in winter in  spite of the        
application of lighted braziers to the  
interior of the  machines4 ,then again1 
the astronomical models and the jackwork

 were  themselves subject to gradual    
improvement3 at the time of ,i-,hsing1  
for  example1 special attention was paid
 to the demarcation of ecliptic as  well
 as the normal equatorial coordinates2  
this was clearly an influx  from        
,hellenistic-,islamic astronomy1 in     
which the relatively  sophisticated     
planetary mathematics had forced this   
change not otherwise  noted in ,china4  
,by the time of the ,jesuits1 this      
current of ,chinese horology1 long since
  utterly destroyed by the perils of    
wars1 storms1 and governmental  reforms1
 had quite been forgotten4 ,matteo      
,ricci's clocks1 those gifts  that      
aroused so much more interest than      
,european theological teachings1  were  
obviously something quite new to the    
#afth-century ,chinese scholars2  so    
much so that they were dubbed with a    
quite new name1 self-sounding  bells1 a 
direct translation of the word clock    
7glokke74 ,in view of  the fact that the
 medieval ,chinese escapement may have  

been the basis of  ,european horology1  
it is a curious twist of fate that the  
high regard of  the ,chinese for        
,european clocks should have prompted   
them to open their  doors1 previously so
 carefully and for so long kept closed  
against the  foreign barbarians4        
,illustration3 ,figure                  
#d4--;,,astronomical ,,clock ,,tower    
,,of ,,su ,,sung in  ,k'ai-feng1 ca4    
,a4,d4 #ajij1 from an original drawing  
by ,john  ,christiansen4 7,courtesy of  
,cambridge ,university ,press47         
,mechanized ,astronomical ,models       
,now that we have seen the manner in    
which mechanized astronomical models    
developed in ,china1 we can detect a    
similar line running from  ,hellenistic 
time1 through ,india and ,islam to the  
medieval ,europe that  inherited their  
learning4 ,there are many differences1  
notably because of  the especial        
development of that peculiar            
characteristic of the ,west1            
mathematical astronomy1 conditioned by  

the almost accidental conflux of        
,babylonian arithmetical methods with   
those of ,greek geometry4 ,however1  the
 lines are surprisingly similar1 with   
the exception only of the  crucial      
invention of the escapement1 a feature  
which seems to be  replaced by the      
influx of ideas connected with perpetual
 motion wheels4      ,,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 authors4 ,because  
of its  importance as a prototype1 we   
give the most relevant passages in      
full4#aa    ,cicero's descriptions of   
,archimedes' planetarium are 7italics   
supplied73      ,gaius ,sulpicius       
,gallus 444 at a time when 444 he       
happened    to be at the house of       
,marcus ,marcellus1 his colleague in    
the consulship #aff ,b4,c41 ordered the 
celestial globe to    be brought out    

which the grandfather of ,marcellus had 
carried off from ,syracuse1 when that   
very rich and    beautiful city was     
taken #bab ,b4,c44444 ,though ,i had    
heard    this globe 7sphaerae7 mentioned
 quite frequently on    account of the  
fame of ,archimedes1 when ,i saw it ,i  
did not    particularly admire it2 for  
that other celestial globe1    also     
constructed by ,archimedes1 which the   
same ,marcellus    placed in the temple 
of ,virtue1 is more beautiful as well   
as more widely known among the people4  
,but when ,gallus    began to give a    
very learned explanation of the device1 
,i    concluded that the famous         
,sicilian had been endowed with         
greater genius than one would imagine   
possible for human    being to possess4 
,for ,gallus told us that the other kind
    of celestial globe1 which was solid 
and contained no    hollow space1 was a 
very early invention1 the first one of  
that kind having been constructed by    
,thales of ,miletus1    and later marked

 by ,eudoxus of ,cnidus--a disciple of  
,plato1 it was claimed--with            
constellations and stars which    are   
fixed in the sky4 ,he also said that    
many years later    ,aratus 444 had     
described it in verse4444 ,but this     
newer    kind of globe1 he said1 on     
which were delineated the    motions of 
the sun and moon and of those five stars
 which    are called wanderers1 or1 as  
we might say1 rovers    i4 e41 the five 
planets1 contained more than could be   
shown on the solid globe1 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 globe1 those various and 
divergent movements with    their       
different rates of speed4 ,and when     
,gallus moved    i4e41 set in motion the
 globe1 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 sky4
 ,thus the same    eclipse of the sun   
happened on the globe as would actually 
happen1 and the moon came to the point  
where the shadow of    the earth was at 
the very time when the sun 7appeared87  
out of the region 444 several pages are 
missing in the    manuscript2 there is  
only one4        ,de republica1 ,i1 xiv 
7#ba-bb71 ,keyes' translation4          
,when ,archimedes put together in a     
globe the movements of    the moon1 sun 
and five wandering planets1 he brought  
about the same effect as that which the 
god of ,plato did    in the ,timaeus    
when he made the world1 so that one     
revolution produced dissimilar movements
 of delay and    acceleration4          
,tusculanae disputationes1 ,i1 #fc4     
,later descriptions from ,ovid1         
,lactantius1 ,claudian1 ,sextus         
,empiricus1  and ,pappus1 respectively1 
are 7italics supplied73      ,there     
stands a globe suspended by a           
,syracusan's skill in    an enclosed    

bronze frame1 or sphere--or perhaps1 in 
enclosed air1 a small image of the      
immense vault of    heaven2 and the     
earth is equally distant from the top   
and    bottom2 that is brought about by 
its i4 e41 the outer    bronze globe's  
round form4 ,the form of the temple of  
,vesta is similar4444        ,ovid1     
,fasti 7#ast century1 ,a4,d471 ,,vi1    
#bgg-bhj1        ,frazer's translation4 
,the ,sicilian ,archimedes1 was able to 
make a reproduction    and model of the 
world in concave brass 7concavo aere    
similitudinem mundi ac figuram72 in it  
he so arranged the    sun and moon and  
resembling the celestial revolutions    
7caelestibus similes conversionibus72   
and while it    revolved it exhibited   
not only the accession and recession    
of the sun and the waxing and waning of 
the moon    7incrementa deminutionesque 
lunae71 but also the unequal    courses 
of the stars1 whether fixed or          
wandering4        ,lactantius1          
,institutiones divinae 7#dth century1   

,a4,d471        ,,ii1 #e1 #ah4          
,archimedes' sphere4 ,when ,jove looked 
down and saw the    heavens figured in a
 sphere of glass1 he laughed and    said
 to the other gods3 ,has the power of   
mortal effort    gone so far8 ,is my    
handiwork now mimicked in a fragile     
globe8 ,an old man of ,syracuse had     
imitated on earth the    laws of the    
heavens1 the order of nature1 and the   
ordinances of the gods4 ,some hidden    
influence within the    sphere directs  
the various courses of the stars and    
actuates the lifelike mass with definite
 motions4 ,a false    zodiac runs       
through a year of its own and a toy moon
    waxes and wanes month by month4 ,now
 bold invention    rejoices to make its 
own heaven revolve and sets the    stars
 planets8 in motion by human wit4444    
,claudian1 ,carmina minora 7ca4 ,a4,d4  
#djj71 ,,li 7,,lxviii71                 
,platnaure's translation4      ,the     
things that move by themselves are more 
wonderful than    those which do not4   

,at any rate1 when we behold an         
,archimedean sphere in which the sun and
 the rest of the    stars move1 we are  
immensely impressed by it1 not by ,zeus 
because we are amazed at the wood1 or at
 the movements    of these bodies1 but  
by the devices and causes of the        
movements4        ,sextus ,empiricus1   
,adversus mathematicos 7#crd century1   
,a4,d471 ,,ix1 #aae1 ,epps' translation4
      ,mechanics understand the making  
of spheres and know how to    produce a 
model of the heavens 7with the courses  
of the    stars moving in circles87 by  
mean of equal and circular    motions of
 water1 and ,archimedes the ,syracusan1 
according to some1 knows the cause and  
reasons for all of    these4            
,pappus 7#crd century1 ,a4,d471 ,works  
7,hultsch edition71      ,,viii1 #b1    
,epps' translation4    ,a similar       
arrangement seems to be indicated in    
another mechanized globe1  also         
mentioned by ,cicero and said to have   
been made by ,posidonius3      ,but if  

anyone brought to ,scythia or ,britain  
the globe    7sphaeram7 which our friend
 ,posidonius of ,apameia1 the    ,stoic 
philosopher recently made1 in which each
 revolution    produced the same        
7movements7 of the sun and moon and     
five wandering stars as is produced in  
the sky each day    and night1 who would
 doubt that it was by exertion of       
reason8444 ,yet doubters 444 think that 
,archimedes showed    more knowledge in 
producing movements by revolutions of a 
globe than nature 7does7 in effecting   
them though the copy    is so infinitely
 inferior to the original4444       ,de 
natura deorum1 ,,ii1 xxxiv-xxxv 7#hh71  
,yonge's translation4    ,in spite of   
the lack of sufficient technical details
 in any case1 these  mechanized globe   
models1 with or without geared planetary
 indicators  7which would make them     
highly complex machines71 bear a        
striking  resemblance to the earliest   
,chinese device described by ,chang     
,hng4 ,one  must not reject the         

possibility that transmission from      
,greece or ,rome  could have reached the
 ,east by the beginning of the #bnd     
century1 ,a4,d41  when he was working4  
,it is an interesting question1 but even
 if such  contact actually occurred1    
very soon afterwards1 as we shall see1  
the  western and eastern lines of       
evolution parted company and evolved so 
far  as can be seen1 quite independently
 until at least the #abth century4      
,the next ,hellenistic source of which  
we must take note is a fragmentary  and 
almost unintelligible chapter in the    
works of ,hero of ,alexandria4  ,alone  
and unconnected with his other chapters 
this describes a model  which seems to  
be static1 in direct contrast to all    
other devices which  move by pneumatic  
and hydrostatic pressures2 it may well  
be conjectured  that in its original    
form this chapter described a mechanized
 rather  than a static globe3      ,the 
,world represented in the ,centre of the
 ,universe3 ,the    construction of a   

transparent globe containing air and    
liquid1 and also of a smaller globe1 in 
the centre1 in    imitation of the      
,world4 ,two hemispheres of glass are   
made2    one of them is covered with a  
plate of bronze1 in the    middle of    
which is a round hole4 ,to fit this hole
 a light    ball1 of small size1 is     
constructed1 and thrown into the        
water contained in the other hemisphere3
 the covered    hemisphere is next      
applied to this1 and1 a certain         
quantity of the liquid having been      
removed from the water1    the          
intermediate space will contain the     
ball2 thus by the    application of the 
second hemisphere what was proposed is  
accomplished4        ,pneumatics1       
,,xlvi1 ,woodcroft's translation4    ,it
 will be noted that these earliest      
literary references are concerned  with 
pictorial1 #c-;dimensional models of the
 universe1 moved perhaps by  hand1      
perhaps by waterpower2 there is no      
evidence that they contained            

complicated trains of gears1 and in the 
absence of this we may incline  to the  
view that in at least the earliest such 
models1 gearing was not  used4    ,the  
next developments were concerned on the 
one hand with increasing the            
mathematical sophistication of the      
model1 on the other hand with its       
mechanical complexity4 ,in both cases we
 are most fortunate in having           
archaeological evidence which far       
exceeds any literary sources4    ,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 thereafter4 
,in  particular1 by the time of ,ptolemy
 7ca4 ,a4,d4 #abj7 it had led to the    
successive inventions of the anaphoric  
clock and of the planispheric           
astrolabe4#ab ,both these devices       
consist of a pair of stereographic      
projections1 one of the celestial sphere
 with its stars and ecliptic and        

tropics1 the other of the lines of      
altitude and azimuth as set for an      
observer in a place at some particular  
latitude4    ,in the astrolabe1 an      
openwork metal rete containing markings 
for the  stars1 etc41 may be rotated by 
hand over a disc on which the lines of  
altitude and azimuth are inscribed4 ,in 
the anaphoric clock a disc  engraved    
with the stars is rotated automatically 
behind a fixed grille  of wires marking 
lines of altitude and azimuth4 ,power   
for rotating the  disc is provided by a 
float rising in a clepsydra jar and     
connected1 by  a rope or chain passing  
over a pulley to a counterweight or by a
 rack  and pinion1 to an axle which     
supported the rotating disc and         
communicated this motion to it4#ac      
,illustration3 ,figure #e4 ,,plate ,,of 
,,salzburg ,,anaphoric ,,clock1 a       
reconstruction 7see footnote #ad7 based 
on a photograph of the remaining        
fragment4 7,courtesy of ,oxford         
,university ,press47    ,parts of two   

such discs from anaphoric clocks have   
been found1 one at  ,salzburg#ad and one
 at ,grand in the ,vosges1#ae both of   
them dating  from the #bnd century      
,a4,d4 ,fortunately there is sufficient 
evidence to  reconstruct the ,salzburg  
disc and show that it must have been    
originally  about #agj cm4 in diameter1 
a heavy sheet of bronze to be turned by 
the  small power provided by a float1   
and a large and impressive device when  
working 7see fig4 #e74 ,literary        
accounts of the anaphoric clock have    
been  analyzed by ,drachmann2 there is  
no evidence of the representation of    
planets moved either by hand or by      
automatic gearing1 only in the          
important case of the sun was such a    
feature included of necessity4 ,a  model
 sun on a pin could be plugged in to any
 one of #cfj holes drilled  in at equal 
intervals along the band of the         
ecliptic4 ,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  night4    ,the      
anaphoric clock is not only the origin  
of the astrolabe and of all  later      
planetary models1 it is also the first  
clock dial1 setting a  standard for     
clockwise rotation1 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     
hand4    ,we come finally to a piece of 
archaeological evidence that surpasses  
all  else4 ,though badly preserved and  
little studied it might well be the     
most important classical object ever    
found2 entailing a complete             
re-estimation of the technical prowess  
of the ,hellenistic ,greeks4 ,in  #aija 
a sunken treasure ship was discovered   
lying off the island of  ,antikythera1  
between ,greece and ,crete4#af ,many    
beautiful classical  works of statuary  
were recovered from it1 and these are   
now amongst the  greatest treasures of  

the ,national ,museum at ,athens1       
,greece4 ,besides  these obviously      
desirable art relics1 there came to the 
surface some  curious pieces of metal1  
accompanied by traces of what may have  
been a  wooden casing4 ,two thousand    
years under the sea had reduced the     
metal to  a mess of corroded fragments  
of plates1 powdered verdigris1 and still
  recognizable pieces of gear wheels4   
,if it were not for the established     
dates for other treasure from this      
ship1 especially the minor objects      
found1 and for traces of inscriptions   
on this metal device written in letters 
agreeing epigraphically with the  other 
objects1 one would have little doubt in 
supposing that such a  complicated piece
 of machinery dated from the #ahth      
century1 at the  earliest4 ,as it is1   
estimates agree on ca4 #fe ,b4,c4 #aj   
years1 and we  can be sure that the     
machine is of ,hellenistic origin1      
possibly from  ,rhodes or ,cos4         
,illustration3 ,figure                  

#f4--;,,antikythera ,,machine1 ,,largest
 ,,fragment4 7,photo  courtesy of       
,national ,museum1 ,athens47    ,the    
inscriptions1 only partly legible1 lead 
one to believe that we are  dealing with
 an astronomical calculating mechanism  
of some sort4 ,this is  born out by the 
mechanical construction evident on the  
fragments4 ,the  largest one 7fig4 #f7  
contains a multiplicity of gearing      
involving an  annular gear working      
epicyclic gearing on a turntable1 a     
crown wheel1  and at least four separate
 trains of smaller gears1 as well as a  
#d-spoked driving wheel4 ,one of the    
smaller fragments 7fig4 #g1 bottom7     
contains a series of movable rings which
 may have served to carry  movable      
scales on one of the three dials4 ,the  
third fragment 7fig4 #g1  top7 has a    
pair of rings carefully engraved and    
graduated in degrees of  the zodiac     
7this is1 incidentally1 the oldest      
engraved scale known1 and  micrometric  
measurements on photographs have        

indicated a maximum  inaccuracy of about
 #a_/b in the #de present74             
,illustration3 ,figure                  
#g4--;,,antikythera ,,machine1 ,,two    
,,smaller ,,fragments4  7,photo courtesy
 of ,national ,museum1 ,athens47        
,unfortunately1 the very difficult task 
of cleaning the fragments is  slow1 and 
no publication has yet given sufficient 
detail for an adequate  explanation of  
this object4 ,one can only say that     
although the problems  of restoration   
and mechanical analysis are peculiarly  
great1 this must  stand as the most     
important scientific artifact preserved 
from  antiquity4    ,some technical     
details can be gleaned however4 ,the    
shape of the gear  teeth appears to be  
almost exactly equilateral triangles in 
all cases  7fig4 #h71 and square shanks 
may be seen at the centers of some of   
the  wheels4 ,no wheel is quite complete
 enough for a count of gear teeth1 but  
a provisional reconstruction by         
,theophanidis 7fig4 #i7 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 speeds4      
,illustration3 ,figure                  
#h4--;,,antikythera ,,machine1 ,,detail 
,,from ,,figure #f1  showing gearing4   
7,photo courtesy of ,national ,museum1  
,athens47    ,thus1 if the evidence of  
the ,antikythera machine is to be taken 
at its  face value1 we have1 already in 
classical times1 the use of astronomical
  devices as complicated as any clock4  
,in any case1 the material supplied  by 
the works ascribed to ,archimedes1      
,hero1 and ,vitruvius1 and the more     
certain evidence of the anaphoric clocks
 is sufficient to show that  there was a
 strong classical tradition of such     
machines1 a tradition  that inspired1   
even if it did not directly influence1  
later developments  in ,islam and       
,europe on the one side1 and1 just      
possibly1 ,china on the  other4         

,note added in proof3      ,since the   
above lines were written1 ,i have been  
privileged    to make a full examination
 of the fragments in the    ,national   
,museum in ,athens4 ,as a result we can 
read much    more inscription and make  
out many more details of the            
mechanism4 ,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 sidereal1     
solar1 lunar1 and    possibly also      
planetary phenomena4 7,see my article in
 the    ,scientific ,american1 ,june    
#aiei1 vol4 #bjj1 ,no4 #f1 pp4          
#fj-fg47 ,relevant to the present study1
 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       
,hellenistic1 ,islamic1 and ,european   
developments are drawn together even    
more tightly4    ,let us now turn our   

attention to those civilizations which  
were  intermediaries1 geographically and
 culturally1 between ,greece and        
medieval ,europe1 and between both of   
these and ,china4 ,from ,india there    
are only two references1 very closely   
related and appearing in the best  known
 astronomical texts in connection with  
descriptions of the  armillary sphere   
and celestial globe4 ,these texts are   
both quite  garbled1 but so far as one  
may understand them1 it seems that the  
types  of spheres and globes mentioned  
are more akin to those current in ,china
  than in the ,west4 ,the relevant      
portions of text are as follows 7italics
  supplied73      ,the circle of the    
horizon is midway of the sphere4 ,as    
covered with a casing and as left       
uncovered1 it is the    sphere          
surrounded by ,lokloka the mountain     
range which    formed the boundary of   
the universe in puranic geography4      
,by the application of water is made    
ascertainment of the    revolution of   

time4 ,one may construct a              
sphere-instrument    combined with      
quicksilver3 this is a mystery2 if      
plainly    described1 it would be       
generally intelligible in the    world4 
,therefore let the supreme sphere be    
constructed    according to the         
instruction of the preceptor guru4 ,in  
each successive age this construction1  
having become lost1    is1 by the ,sun's
 favour1 again revealed to some one or  
other1 at his pleasure4 ,so also1 one   
should construct    instruments in order
 to ascertain time4 ,when quite alone1  
one should apply quicksilver to the     
wonder-causing    instrument4 ,by the   
gnomon1 staff1 arc1 wheel1 instruments  
for taking the shadow of various        
kinds4444 ,by    water-instruments1 the 
vessel1 by the peacock1 man1    monkey1 
and by stringed sand-receptacles one may
 determine    time accurately4          
,quicksilver-holes1 water1 and cords1   
and    oil and water1 mercury and sand  
are used in these3 these                

applications1 too1 are difficult4       
,srya ,siddhnta1 xiii1 #ae-bb1          
,e4 ,burgess' translation1 ,new ,haven1 
#ahfj4    ,illustration3 ,figure        
#i4--;,,antikythera ,,machine1 ,,partial
 ,,reconstruction  ,,by ,,theophanidis  
7see footnote #af74      ,a             
self-revolving instrument or swayanvaha 
yantra3 ,make a    wheel of light wood  
and in its circumference put hollow     
spokes all having bores of the same     
diameter1 and let them    be placed at  
equal distances from each other2 and let
    them also be placed at an angle     
verging somewhat from the               
perpendicular3 then half fill these     
hollow spokes with    mercury2 the wheel
 thus filled will1 when placed on an    
axis supported by two posts1 revolve of 
itself4      ,or scoop out a canal in   
the tire of the wheel and then          
plastering leaves of the ,tla tree over 
this canal with    wax1 fill one half of
 this canal with water and the other    
half with mercury1 till the water begins

 to come out1 and    then cork up the   
orifice left open for filling the wheel4
    ,the wheel will then revolve of     
itself1 drawn around by the    water4   
,description of a syphon3 ,make up a    
tube of copper or other    metal1 and   
bend it in the form of an ,ankus'a or   
elephant    hook1 fill it with water and
 stop up both ends4 ,and then    putting
 one end into a reservoir of water let  
the other    end remain suspended       
outside4 ,now uncork both ends4 ,the    
water of the reservoir will be wholly   
sucked up and fall    outside4      ,now
 attach to the rim of the before        
described    self-revolving wheel a     
number of water-pots1 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   
motion1 impelled by the    additional   
weight of the pots thus filled4 ,the    
water    discharge from the pots as they
 reach the bottom of the    revolving   

wheel1 should be drawn off into the     
reservoir    before alluded to by means 
of a water-course or pipe4      ,the    
self-revolving machine mentioned by     
,lalla1 etc4    which has a tube with   
its lower end open is a vulgar          
machine on account of its being         
dependant1 because that    which        
manifests an ingenious and not a rustic 
contrivance    is said to be a machine4 
,and moreover many self-revolving       
machines are to be met    with1 but     
their motion is procured by a trick4    
,they are    not connected with the     
subject under discussion4 ,i have       
been induced to mention the construction
 of these1 merely    because they have  
been mentioned by former astronomers4   
,siddhnta ,siromai1 xi1 #ej-eg1 ,l4     
,wilkinson's        translation1 revised
 by ,bpu deva ,s7h7stri1                
,calcutta1 #ahfa4    ,before proceeding 
to an investigation of the content of   
these texts it  is of considerable      
importance to establish dates for them1 

though there  are many difficulties in  
establishing any chronology for ,hindu  
astronomy4 ,the ,srya ,siddhnta is known
 to date1 in its original  form1 from   
the early ,middle ,ages1 ca4 #ejj4 ,the 
section in question is  however quite   
evidently an interpolation from a later 
recension1 most  probably that which    
established the complete text as it now 
stands2 it  has been variously dated as 
ca4 #ajjj to ca4 #aaej ,a4,d4 ,the date 
of  the ,siddhnta ,siromai is more      
certain for we know it was  written in  
about #aaej by ,bhskara 7born #aaad74   
,thus both these  passages must have    
been written within a century of the    
great clock-tower  made by ,su ,sung4   
,the technical details will lead us to  
suppose there is  more than a temporal  
connection4    ,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 practice4   
,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   
texts4 ,both texts seem  conscious of   
the complexity of these devices and     
there is a hint 7it is  lost and        
revealed7 that the story has been       
transmitted1 only half  understood1 from
 another age or culture4 ,it should also
 be noted that  the mentions of cords   
and strings rather than gears1 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  devices1  
or with the ,chinese practice4    ,a    
quite new and important note is injected
 by the passage from the  ,bhskara text4
 ,obviously intrusive in this           
astronomical text we have  the          
description of two perpetual motion     
wheels together with a third1           
castigated by the author1 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 wheel4 ,these seem 
to be the basis also1 in the  extract   
from the ,srya ,siddhnta1 of the        
wonder-causing  instrument to which     
mercury must be applied4    ,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 ,europe4 ,at each          
occurrence1 as here1  there are echoes  
of other cultures4 ,in addition to those
 already  mentioned we find the         
otherwise mysterious peacock1 man and   
monkey1  cited as parts of the jackwork 
of astronomical clocks of ,islam1       
associated with the weight drive so     
essential to the later horology in      
,europe4    ,we have already seen that  
in classical times there were already   
two  different types of protoclocks2    
one1 which may be termed                
nonmathematical1 designed only to give a
 visual aid in the conception  of the   

cosmos1 the other1 which may be termed  
mathematical in which  stereographic    
projection or gearing was employed to   
make the device a  quantitative rather  
than qualitative representation4 ,these 
two lines  occur again in the ,islamic  
culture area4    ,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 formation4 
,procopius 7died ca4 #ece7 describes a  
monumental water clock which was        
erected in ,gaza ca4 #ejj4ag ,it        
contained impressive jackwork1 such as  
a ,medusa head which rolled its eyes    
every hour on the hour1 exhibiting  the 
time through lighted apertures and      
showing mythological  interpretations of
 the cosmos4 ,all these effects were    
produced by  ,heronic techniques1 using 
hydraulic power and puppets moved by    
strings1  rather than with gearing4     
,again in #hjg a similarly marvelous    

exhibition clock made of bronze was     
sent by ,harun-al-,rashid to the        
,emperor ,charlemagne2 it seems to have 
been of the same type1 with automata and
 hydraulic works4 ,for the  succeeding  
few centuries1 ,islam was in its ,golden
 ,age of development of  technical      
astronomy 7ca4 #iej-aaej7 and attention 
may have been  concentrated on the more 
mathematical protoclocks4 ,towards the  
end of  the #abth century1 however1     
there was a revival of the old          
tradition1  mainly at the court of the  
,emperor ,saladin 7#aadf-aagc7 when a   
great  automaton water clock1 more      
magnificent than any hitherto1 was      
erected  in ,damascus4 ,it was rebuilt1 
after #aafh1 by ,muammad b4 ',al b4     
,rustum1 and repaired and improved by   
his son1 ,fakhr ad-dn  ,riwn b4         
,muammad1#ah who is most important as   
the author of  a book which describes in
 considerable technical detail the      
construction  of this and other         
protoclocks4 ,closely associated with   

his book one also  finds texts dealing  
with perpetual-motion devices1 which we 
shall  consider later4    ,during the   
century following this horological      
exuberance in ,damascus1  the center of 
gravity of ,islamic astronomy shifted   
from the ,east to the  ,hispano-,moorish
 ,west4 ,at the same time there comes   
more evidence that  the line of         
mathematical protoclocks had not been   
left unattended4 ,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        
,riwn3#ai      ,in the same year #abcb  
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 ducats4 ,for it        
appeared to resemble internally a       
celestial globe in which figures of the 
sun1 moon1 and    other planets formed  

with the greatest skill moved1 being    
impelled by weights and wheels1 so that 
performing their    course in certain   
and fixed intervals they pointed out the
    hour night and day with infallible  
certainty2 also the    twelve signs of  
the zodiac with certain appropriate     
characters1 moved with the firmament1   
contained within    themselves the      
course of the planets4    ,illustration3
 ,figure #aj4--;,,calendrical ,,gearing 
,,designed ,,by ,,al-,,biruni1  ca4     
,a4,d4 #ajjj4 ,the gear train count is  
#dj-ajg-eiai-eibd-dh4 ,the  gear of #dh 
therefore makes #ai 7annual7 rotations  
while that of #ai-ei  shows #aah double 
lunations of #bicjei days4 ,the gear of 
#dj shows a  7lunar7 rotation in exactly
 #bh days1 and the center pinions #gaj  
rotate  in exactly one week4 ,after     
,wiedemann 7see footnote #bj74    ,the  
phrase resembled internally is of       
especial interest in this  passage2 it  
may perhaps arise as a mistranslation of
 the technical term  for stereographic  

projection of the sphere1 and if so the 
device might  have been an anaphoric    
clock or some other astrolabic device4  
,this is made more probable by the      
existence of a specifically ,islamic    
concentration on the astrolabe1 and on  
its planetary companion  instrument1 the
 equatorium1 as devices for mechanizing 
computation by  use of geometrical      
analogues4 ,the ordinary planispheric   
astrolabe1 of  course1 was known in     
,islam from its first days until almost 
the present  time4 ,from the time of    
al-,biruni 7ca4 #ajjj7--significantly1  
perhaps1  he is well known for his      
travel account of ,india--there is      
remarkable  innovation4    ,most cogent 
to our purpose is a text1 described for 
the first time by  ,wiedemann1#bj 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 moon1        
features of fundamental importance in   

the ,islamic 7lunar7 calendrical        
system4 ,this device necessarily uses   
gear wheels with an odd number of  teeth
 7e4g41 #g1 #ai1 #ei7 as dictated by the
 astronomical constants  involved 7see  
fig4 #aj74 ,the teeth are shaped like   
equilateral triangles  and square shanks
 are used1 exactly as with the          
,antikythera machine4  ,horse-headed    
wedges are used for fixing2 a tradition 
borrowed from the  horse-shaped ,fars   
used to fasten the traditional          
astrolabe4 ,of  special interest for us 
is the lunar phase diagram1 which is    
just the  same in form and structure as 
the lunar volvelle that occurs later in 
horology and is still so commonly found 
today1 especially as a  decoration for  
the dial of grandfather clocks4         
,illustration3 ,figure #aa4--;,,geared  
,,astrolabe ,,by ,,mu,,ammad ,b4 ,,ab   
,,bakr  ,,of ,,isfahan1 ,a4,d4          
#abba-abbb4 7,photo courtesy of ,science
 ,museum1  ,london47    ,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 clocks4 ,from the        
manuscript description alone one  could 
not tell whether it was designed for    
automatic action or merely to  be turned
 by hand4 ,fortunately this point is    
made clear by the most  happy survival  
of an intact specimen of this very      
device1 without doubt  the oldest geared
 machine in existence in a complete     
state4    ,illustration3 ,figure        
#ab4--;,,gearing ,,from ,,astrolabe     
,,shown ,,in ,,figure #aa4  ,the gear   
train count is as follows3              
#dh-ach-fdfd-fdaj-fj4 ,the pinion  of #h
 has been incorrectly replaced by a more
 modern pinion of #aj4 ,the  gear of #dh
 should make #ac 7lunar7 rotations while
 the double gear of  #fdfd makes #f     
revolutions of double months 7of #bi-cj 
days7 and the gear  of #fj makes a      
single turn in the hegiral year of #ced 
days4 7,photo  courtesy of ,science     

,museum1 ,london47    ,this landmark in 
the history of science and technology is
 now preserved  at the ,museum of the   
,history of ,science1 ,oxford1          
,england4#ba ,it is an  astrolabe1 dated
 #abba-bb and signed by the maker1      
,muammad b4 ,ab  ,bakr 7died #abca-cb7  
of ,isfahan1 ,persia 7see figs4 #aa and 
#ab74 ,the very  close resemblance to   
the design of ,biruni is quite apparent1
 though the  gearing has been simplified
 very cleverly so that only one wheel   
has an  odd number of teeth 7#ac71 the  
rest being much easier to mark out      
geometrically 7e4g41 #aj1 #dh1 #fj1 and 
#fd teeth74 ,the lunar phase  volvelle  
can be seen through the circular opening
 at the back of the  astrolabe4 ,it is  
quite certain that no automatic action  
is intended2  when the central pivot is 
turned1 by hand1 probably by using the  
astrolabe rete as a handle1 the         
calendrical circles and the lunar  phase
 are moved accordingly4 ,using one turn 
for a day would be too slow  for useful 

re-setting of the instrument1 in        
practice a turn corresponds  more nearly
 to an interval of one week4            
,illustration3 ,figure                  
#ac4--;,,astrolabe ,,clock1 ,,regulated 
,,by ,a ,,mercury ,,drum1  from the     
,alfonsine ,libros del saber 7see       
footnote #bb74    ,in addition to this  
geared development of the astrolabe1 the
 same period  in ,islam brought forth a 
new device1 the equatorium1 a mechanical
 model  designed to simulate the        
geometrical constructions used for      
finding the  positions of the planets in
 ,ptolemaic astronomy4 ,the method may  
have  originated already in classical   
times1 a simple device being described  
by ,proclus ,diadochus 7ca4 #dej71 but  
the first general1 though crude1        
planetary equatorium seems to have been 
described by ,abulcacim ,abnacahm  7ca4 
#ajbe7 in ,granada2 it has been handed  
down to us in the archaic  ,castilian of
 the ,alfonsine ,libros del saber4#bb   
,the sections of this  book1 dealing    

with the ,laminas de las ,,vii          
,planetas1 describe not only  this      
instrument but also the improved        
modification introduced by  ,azarchiel  
7born ca4 #ajbi1 died ca4 #ajhg74    ,no
 ,islamic examples of the equatorium    
have survived1 but from this  period    
onward1 there appears to have been a    
long and active tradition of  them1 and 
ultimately they were transmitted to the 
,west1 along with the  rest of the      
,alfonsine corpus4 ,more important for  
our argument is that  they were the     
basis for the mechanized astronomical   
models of ,richard of  ,wallingford 7ca4
 #acbj7 and probably others1 and for the
 already  mentioned great astronomical  
clock of de ,dondi4 ,in fact1 the       
complicated  gearwork and dials of de   
,dondi's clock constitute a series of   
equatoria1  mechanized in just the same 
way as the calendrical device described 
by  ,biruni4    ,it is evident that we  
are coming nearer now to the beginning  
of the true  mechanical clock1 and our  

last step1 also from the ,alfonsine     
corpus of  western ,islam1 provides us  
with an important link between the      
anaphoric  clock1 the weight drive1 and 
a most curious perpetual-motion device1 
the  mercury wheel1 used as an          
escapement or regulator4 ,the ,alfonsine
 book on  clocks contains descriptions  
of five devices in all1 four of them    
being  due to ,isaac b4 ,sid 7two       
sundials1 an automaton water-clock and  
the  present mercury clock7 and one to  
,samuel ha-,levi ,adulafia 7a candle    
clock7--they were probably composed just
 before ca4 #abgf-gg4    ,illustration3 
,figure #ad4--;,,islamic ,,perpetual    
,,motion ,,wheel1 after  manuscript     
cited by ,schmeller 7see footnote #bf74 
,the mercury clock of ,isaac b4 ,sid    
consists of an astrolabe dial1 rotated  
as in the anaphoric clock1 and fitted   
with #cj leaf-shaped gear teeth  7see   
fig4 #ac74 ,these are driven by a pinion
 of #f leaves mounted on a  horizontal  
axle 7shown very diagrammatically in the

 illustration7 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 drive4    ,it
 is the mercury drum which forms the    
most novel feature of this  device2 the 
fluid1 constrained in #ab chambers so as
 to just fill #f of  them1 must slowly  
filter through small holes in the       
constraining walls4  ,in practice1 of   
course1 the top mercury surfaces will   
not be level1 but  higher on the right  
so as to balance dynamically the moment 
of the  applied weight on its driven    
rope4 ,this curious arrangement shows   
point  of resemblance to the ,indian    
mercury-holes1 to the perpetual-motion  
devices found in the medieval ,european 
tradition and also in the texts         
associated with ,riwn1 which we shall   
next examine4    ,illustration3 ,figure 
#ae4--;,,another ,,perpetual ,,motion   
,,wheel1 after the  text cited in figure
 #ad4    ,it is of the greatest interest
 to our theme that the ,islamic         

contributions to horology and perpetual 
motion seem to form a closely  knit     
corpus4 ,a most important series of     
horological texts1 including  those of  
,riwn and al-,jazar1 have been edited by
 ,wiedemann  and ,hauser4#bc ,other     
,islamic texts give versions of the     
water clocks  and automata of           
,archimedes and of ,hero and ,philo of  
,alexandria4#bd ,in  at least three     
cases#be these texts are found also     
associated with  texts describing       
perpetual-motion wheels and other       
hydraulic devices4  ,three manuscripts  
of this type have been published in     
,german translation  by ,schmeller4#bf  
,the devices include a many chambered   
wheel 7see fig4  #ad7 similar to the    
,alfonsine mercury escapement1 a wheel  
of slanting  tubes constructed like the 
noria 7see fig4 #ae71 wheels of weights 
swinging on arms as described by        
,villard of ,honnecourt1 and a          
remarkable  device which seems to be the
 earliest known example of a weight     

drive4  ,this latter machine is a pump1 
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 7see fig4 #af72 perhaps  
for balance1 the whole  arrangement is  
made in duplicate with common axles for 
the corresponding  parts4               
,illustration3 ,figure #af4--;,,islamic 
,,pump ,,powered ,,by ,a ,,weight       
,,drive1  after the text cited in figure
 #ad4    ,the ,islamic tradition of     
water clocks did not involve the use of 
gears1  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 automata4 ,in  the   
main1 everything is worked by floats and
 strings or by hydraulic or  pneumatic  
forces1 as in ,heros devices4 ,the      
automata are very elaborate1  with      
figures of men1 monkeys1 peacocks1 etc41
 symbolizing the passage of  hours4     
,,medieval ,,europe    ,echoes from     
nearly all the developments already     

noted from other parts  of the world are
 found to occur in medieval ,europe1    
often coming  through channels of       
communication more precisely            
determinable than  those hitherto       
mentioned4 ,before the influx of        
,islamic learning at the  time of       
transmission of the ,toledo ,tables     
7#abth century7 and the  ,alfonsine     
,tables 7which reached ,paris ca4       
#abib71 there are occasional  references
 to the most primitive mechanized visual
 aids in astronomy4    ,the most famous 
of these occurs in an historical account
 by ,richer of  ,rheims about his       
teacher ,gerbert 7born #idf1 later ,pope
 ,sylvester ,,ii1  #iij-ajjc74 ,several 
instruments made by ,gerbert are        
described in detail2  he includes a fine
 celestial globe made of wood covered   
with horsehide  and having the stars and
 lines painted in color1 and an         
armillary sphere  having sighting tubes 
similar to those always found on        
,chinese  instruments but never on the  

,ptolemaic variety4 ,lastly1 he cites   
the  construction of a sphere1 most     
suitable for recognizing the planets1   
but unfortunately it is not clear from  
the description whether or not  the     
model planets were actually to be       
animated mechanically4 ,the text        
runs3#bg      ,within this oblique      
circle 7the zodiac on the ecliptic of   
the globe7 he hung the circles of the   
wandering stars 7the    planets7 with   
marvellous ingenuity1 whose orbits1     
heights    and even the distance from   
each other he demonstrated to    his    
pupils most effectually4 ,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 theme4    ,thus1 although 
there is a hint of mechanical           
complexity1 there is really  no         
justification for such an assumption2   
the description might well  imply only a
 zodiac band on which the orbits of the 
planets were  painted4 ,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 scholarship4       
,once the floodgates of ,arabic learning
 were opened1 a stream of  mechanized   
astronomical models poured into ,europe4
 ,astrolabes and  equatoria rapidly     
became very popular1 mainly through the 
reason for  which they had been first   
devised1 the avoidance of tedious       
written  computation4 ,many medieval    
astrolabes have survived1 and at least  
three  medieval equatoria are known4    
,chaucer is well known for his treatise 
on  the astrolabe2 a manuscript in      
,cambridge1 containing a companion      
treatise on the equatorium1 has been    
tentatively suggested by the  present   
author as also being the work of        
,chaucer and the only piece  written in 

his own hand4    ,the geared astrolabe  
of al-,biruni is another type of        
protoclock to have  been transmitted4 ,a
 specimen in the ,science ,museum1      
,london1#bh though  unfortunately now   
incomplete1 has a very sophistocated    
arrangement of  gears for moving        
pointers to indicate the correct        
relative positions and  movements of the
 sun and moon 7see figs4 #ag and #ah74  
,like the earlier  ,muslim example it   
contains wheels with odd numbers of gear
 teeth 7#ad1  #bg1 #ci72 however1 the   
teeth are no longer equilateral in      
shape1 but  approximate a more modern   
slightly rounded form4 ,this example is 
,french  and appears to date from ca4   
#acjj4 ,another ,gothic astrolabe with a
  similar gear ring on the rete1 said to
 date from ca4 #adjj 7it could  well be 
much earlier7 is now in the ,billmeier  
collection 7,london74#bi    ,turning    
from the mechanized astrolabe to the    
mechanized equatorium1 we  find the work
 of ,richard of ,wallingford            

7#abib8-accf7 of the greatest  interest 
as providing an immediate precursor to  
that of de ,dondi4 ,he  was the son of  
an ingenious blacksmith1 making his way 
to ,merton  ,college1 ,oxford1 then the 
most active and original school of      
astronomy  in ,europe1 and winning later
 distinction as ,abbot of ,st4 ,albans4 
,a text  by him1 dated #acbf-bg1        
described in detail the construction of 
a great  equatorium1 more exact and much
 more elaborate than any that had gone  
before4#cj ,nevertheless it is evidently
 a normal manually operated  device like
 all the others4 ,in addition to this   
instrument1 ,richard is  said to have   
constructed ca4 #acbj1 a fine planetary 
clock for his  ,abbey4#ca ,bale1 who    
seems to have seen it1 regarded it as   
without rival  in ,europe1 and the      
greatest curiosity of his time4         
,unfortunately1 the  issue was confused 
by ,leland1 who identified it as the    
,albion 7i4e41  all-by one71 the name   
,richard gives to his manual equatorium4

 ,this clock  was indeed so complex that
 ,edward ,,iii censured the ,abbot for  
spending so  much money on it1 but      
,richard replied that after his death   
nobody would  be able to make such a    
thing again4 ,he is said to have left a 
text  describing the construction of    
this clock1 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 clock4    ,illustration3     
,figure #ag4--;,,french ,,geared        
,,astrolabe ,,of ,,trefoil ,,gothic     
,,design1 ca4 ,a4,d4 #acjj4 ,the gearing
 on the pointer is1 from the  center3   
7#cb7_/ad-debg-ci1 the last meshing with
 a concave annular gear  of #ahj teeth  
around the rim of the rete of the       
astrolabe4 ,a second  pointer1 geared to
 this so as to follow the ,moon1 seems  
to be lacking4  7,photo courtesy of     
,science ,museum4 ,london47             
,illustration3 ,figure #ah4--;,,gear    
,,train ,,of ,,pointer in figure #ag4   

7,photo  courtesy of ,science ,museum1  
,london47    ,a corrective for this view
 is to be had from a ,st4 ,albans       
manuscript  7now at ,gonville and ,caius
 ,college1 ,cambridge7 that described   
the  methods for setting out toothed    
wheels for an astronomical horologium   
designed to show the motions of the     
planets4 ,although the manuscript  copy 
is to be dated ca4 #acdj1 it clearly    
indicates that a geared  planetary      
device was known in ,st4 ,albans at an  
early date1 and it is  reasonable to    
suppose that this was in fact the       
machine made by ,richard  of            
,wallingford4 ,unfortunately the text   
does not appear to give any  relevant   
information about the presence of an    
escapement or any other  regulatory     
device1 nor does it mention the source  
of power4#cb ,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  clock1 and for this reason we   

suggest now that the two clocks were    
very  closely related in other ways too4
 ,this1 circumstantial though it be1 is 
evidence for thinking that the weight   
drive and some form of escapement  were 
known to ,richard of ,wallingford1 ca4  
#acbj4 ,it would narrow the  gap between
 the clock and the protoclocks to less  
than half a century1  perhaps a single  
generation1 in the interval ca4         
#abhe-acbj4 ,in this  connection it may 
be of interest that ,richard of         
,wallingford knew only  the ,toledo     
tables corpus1 that of the ,alfonsine   
school did not arrive in  ,england until
 after his death4    ,there are1 of     
course1 many literary references to the 
water-clocks in  medieval literature4   
,in fact most of these are from         
quotations which  have often been       
produced erroneously in the history of  
the mechanical  clock1 thereby providing
 many misleading starts for that        
history1 as  noted previously in the    
discussion of the horologium4 ,there are

 however  enough mentions to make it    
certain that water clocks of some sort  
were  in use1 especially for            
ecclesiastic purposes1 from the end of  
the #abth  century onwards4 ,thus1      
,jocelin of ,brakelond tells of a fire  
in the ,abbey  ,church of ,bury ,st4    
,edmunds in the year #aaih4cc ,the      
relics would have  been destroyed during
 the night1 but just at the crucial     
moment the  clock bell sounded for      
matins and the master of the vestry     
sounded the  alarm4 ,on this the young  
men amongst us ran to get water1 some to
 the  well and others to the            
clock--probably the sole occasion on    
which a  clock served as a fire hydrant4
    ,it seems probable that some of     
these water clocks could have been      
simple  drip clepsydras1 with perhaps a 
striking arrangement added4 ,a most     
fortunate discovery by ,drover has now  
brought to light a manuscript           
illumination that shows that these water
 clocks1 at least by ca1 #abhe1  had    

become more complex and were rather     
similar in appearance to the  ,alfonsine
 mercury drum4#cd ,the illustration     
7fig4 #ai7 is from a  moralized ,bible  
written in northern ,france1 and        
accompanies the passage  where ,king    
,hezekiah is given a sign by the ,lord1 
the sun being moved  back ten steps of  
the clock4 ,the picture clearly shows   
the central water  wheel and below it a 
dog's head spout gushing water into a   
bucket  supported by chains1 with a     
7weight87 cord running behind4 ,above   
the  wheel is a carillon of bells1 and  
to one side a rosette which might be a  
fly or a model sun4 ,the wheel appears  
to have #ae compartments1 each with  a  
central hole 7perhaps similar to that in
 the ,alfonsine clock7 and it  is       
supported on a square axle by a bracket1
 the axle being wedged in the           
traditional fashion4 ,the projections at
 the edge of the wheel might be  gear   
teeth1 but more likely they are used    
only for tripping the striking          

mechanism4 ,if it were not for the      
running water spout it would be very    
close to the ,alfonsine model2 but with 
this evidence it seems impossible  to   
arrive at a clear mechanical            
interpretation4    ,from the adjacent   
region there is another account of a    
striking water  clock1 the evidence     
being inscriptions on slates1 discovered
 in ,villers  ,abbey near ,brussels2#ce 
these may be closely dated as #abfg or  
#abfh and  provide the remains of a     
memorandum for the sacrist and his      
assistants  in charge of the clock4     
,always set the clock1 however long you 
may delay on the    letter ,a afterwards
 you shall pour water from the    little
 pot 7pottulo7 that is there1 into the  
reservoir    7cacabum7 until it reaches 
the prescribed level1 and you    must do
 the same when you set the clock after  
compline    so that you may sleep       
soundly4    ,a quite different sort of  
evidence is to be had from the writings 
of  ,robertus ,anglicus in #abga 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 heavens3#cf      ,nor  
it is possible for any clock to follow  
the judgment of    astronomy with       
complete accuracy4 ,yet clockmakers     
7artifices horologiorum7 are trying to  
make a wheel    7circulum7 which will   
make one complete revolution for        
every one of the equinoctial circle1 but
 they cannot quite    perfect their     
work4 ,but if they could1 it would be a 
really accurate clock 7horologium verax 
valde7 and worth    more than an        
astrolabe or other astronomical         
instrument    for reckoning the hours1  
if one knew how to do this    according 
to the method aforesaid4 ,the method of 
making    such a clock would be this1   
that a man make a disc    7circulum7 of 
uniform weight in every part so far as  

could    possibly be done4 ,then a lead 
weight should be hung from    the axis  
of that wheel 7axi ipsius rote7 and this
 weight    would move that wheel so that
 it would complete one    revolution    
from sunrise to sunrise1 minus as much  
time as    about one degree rises       
according to an approximately    correct
 estimate4 ,for from sunrise to sunrise1
 the whole    equinoctial rises1 and    
about one degree more1 through    which 
degree the sun moves against the motion 
of the    firmament in the course of a  
natural day4 ,moreover1 this    could be
 done more accurately if an astrolabe   
were    constructed with a network on   
which the entire equinoctial    circle  
was divided up4    ,illustration3       
,figure #ai4--,,manuscript              
,,illumination ,,of ,a ,,medieval       
,,waterclock1 showing a partitioned     
wheel1 a weight drive1 and a carillion  
for striking4 ,from ,drover 7see        
footnote #cd74    ,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 7because of the 
annual rotation of the sun amongst the  
stars7 but it gives no indication of any
 regulatory device4 ,again it  should be
 noted1 this source comes from ,france2 
,robertus1 though of  ,english origin1  
apparently being then a lecturer either 
at the  ,university of ,paris or at that
 of ,montpellier4 ,the date of this     
passage1  #abga1 has been taken as a    
terminus post quem for the invention of 
the  mechanical clock4 ,in the next     
section we shall describe the text of   
,peter ,peregrinus1 very close to this  
in place and date1 which describes  just
 such a machine1 conflating it with     
accounts of an armillary sphere1        
perpetual motion1 and the magnetic      
compass--so bringing all these  threads 
together for the first time in ,europe4 
,illustration3 ,figure                  
#bj4--;,,arrangement ,,for ,,turning ,a 
,,figure ,,of ,,an ,,angel4  ,it has    

been alleged that this drawing by       
,villard represents an  escapement4     
,after ,lassus 7see footnote #cg74      
,we have reserved to the last one       
section of evidence which may or may    
not be misleading1 the famous notebook  
of ,villard 7,wilars7 of  ,honnecourt1  
near ,cambrai4 ,the album1 attributed to
 the period #abdj-abea1  contains many  
drawings with short annotations1 three  
of which are of  special interest to our
 investigations4#cg ,these comprise a   
steeplelike  structure labeled cest li  
masons don orologe 7this is the house of
 a  clock71 a device including a rope1  
wheel and axle 7fig4 #bj71 marked par   
chu fait om un angle tenir son doit ades
 vers le solel 7by this means  an angel 
is made to keep his finger directed     
towards the sun71 and a  perpetual      
motion wheel which we shall reserve for 
later discussion4    ,the clock tower1  
according to ,drover1 shows no place for
 a dial but  suggests the use of bells  
because of its open structure1 suitable 

for  letting out the sound4 ,moreover1  
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  church4 ,there is1
 alas1 nothing to tell us about the     
clock it was  intended to house2 most   
probably it was a water clock similar to
 that of  the illustrated ,bible of ca4 
#abhe4    ,the drawing of the rope1     
wheel and axles1 for turning an angel to
 point  towards the sun can have a      
simple explanation or a more complicated
 one4  ,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    
turns1 thereby moving 7by hand7 the     
figure of an angel 7not shown7  fixed to
 the top of this latter shaft4 ,such an 
explanation was in fact  suggested by   
,m4 ,quicherat1#ch who first called     
attention to the ,villard  album and    
pointed out that a leaden angel existed 

in ,chartres before the  fire there in  
#ahcf4 ,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 ,gospel4 ,slight pressure on the    
tail of the  bird causes a similar rope 
mechanism to operate4    ,a quite       
different interpretation has been       
suggested by ,frmont2#ci he  believes   
that the wheel may have acted as a      
fly-wheel and the ropes and             
counterpoises1 turning first one way    
then the other acted as a sort of       
mechanical escapement4 ,such an         
arrangement is however mechanically     
impossible without some complicated     
free-wheeling device between the  drive 
and the escapement1 and its only effect 
would be to oscillate the  angel rapidly
 rather than turn it steadily4 ,i       
believe that ,frmont1  over-anxious to  
provide a protoescapement1 has done too 
much violence to  the facts and turned  
away without good reason from the more  

simple and  reasonable explanation4 ,it 
is nevertheless still possible to adopt 
this  simple interpretation and yet to  
have the system as part of a clock4 ,if 
the left-hand counterpoise1 conveniently
 raised higher than that on the  right1 
is considered as a float fitting into a 
clepsydra jar1 instead of  as a simple  
weight1 one would have a very suitable  
automatic system for  turning the angel4
 ,on this explanation1 the purpose of   
the wheel would  be merely to provide   
the manual adjustment necessary to set  
the angel  from time to time1           
compensating for irremediable           
inaccuracies of the  clepsydra4         
,illustration3 ,figure                  
#ba4--,,villard',s ,,perpetual ,,motion 
,,wheel1 from ,lassus  7see footnote    
#cg74    ,having discussed the ,villard 
drawings which are already cited in     
horological literature1 we must draw    
attention to the fact that this         
medieval architect also gives an        
illustration of a perpetual motion      

wheel4 ,in this case 7fig4 #ba7 it is of
 the type having weights at the  end of 
swinging arms1 a type that occurs very  
frequently at later dates  in ,europe   
and is also given in the ,islamic texts4
 ,we cannot1 in this  case1 suggest that
 drawings of clocks and of perpetual    
motion devices  occur together by more  
than a coincidence1 for ,villard seems  
to have  been interested in most sorts  
of mechanical device4 ,but even this    
type  of coincidence becomes somewhat   
striking when repeated often enough4 ,it
  seems that each early mention of      
self-moving wheels occurs in  connection
 with some sort of clock or mechanized  
astronomical device4    ,having now     
completed a survey of the traditions of 
astronomical models1  we have seen that 
many types of device embodying features 
later found in  mechanical clocks       
evolved through various cultures and    
flowed into  ,europe1 coming together in
 a burst of multifarious activity during
 the  second half of the #acth century1 

notably in the region of ,france4 ,we   
must now attempt to fill the residual   
gap1 and in so doing examine the        
importance of perpetual motion devices1 
mechanical and magnetic1 in the  crucial
 transition from protoclock to          
mechanical-escapement clock4            
,perpetual ,motion and the ,clock before
 de ,dondi    ,we have already noted1   
more or less briefly1 several instances 
of the  use of wheels moving by         
themselves or the use of a fluid for    
purposes  other than as a motive power4 
,chronologically arranged1 these are the
  ,indian devices of ca4 #aaej or a     
little earlier1 as those of ,riwn  ca4  
#abjj1 that of the ,alfonsine mercury   
clock1 ca4 #abgb1 and the  ,french      
,bible illumination of ca4 #abhe4 ,this 
strongly suggests a steady  transmission
 from ,east to ,west1 and on the basis  
of it1 we now  tentatively propose an   
additional step1 a transmission from    
,china to  ,india and perhaps further   
,west1 ca4 #aajj1 and possibly          

reinforced by  further transmissions at 
later dates4    ,one need only assume   
the existence of vague traveler's tales 
about the  existence of the             
#aath-century ,chinese clocks with their
 astronomical  models and jackwork and  
with their great wheel1 apparently      
moving by  itself but using water having
 no external inlet or outlet4 ,such a   
stimulus1 acting as it did on a later   
occasion when ,galileo received  word of
 the invention of the telescope in the  
,low ,countries1 might  easily lead to  
the re-invention of just such           
perpetual-motion wheels as  we have     
already noted4 ,in many ways1 once the  
idea has been suggested it  is natural  
to associate such a perpetual motion    
with the incessant  diurnal rotation of 
the heavens4 ,without some such stimulus
 however it  is difficult to explain why
 this association did not occur earlier1
 and  why1 once it comes there seems to 
be such a chronological procession  from
 culture to culture4    ,we now turn to 

what is undoubtedly the most curious    
part of this story1  in which           
automatically moving astronomical models
 and perpetual motion  wheels are linked
 with the earliest texts on magnetism   
and the magnetic  compass1 another      
subject with a singularly troubled      
historical origin4  ,the key text in    
this is the famous ,epistle on the      
magnet1 written by  ,peter ,peregrinus1 
a ,picard1 in an army camp at the ,siege
 of ,lucera and  dated ,august #h1      
#abfi4dj ,in spite of the precise dating
 it is certain  that the work was done  
long before1 for it is quoted           
unmistakably by  ,roger ,bacon in at    
least three places1 one of which must   
have been  written before ca4 #abej4da  
,the ,epistle contains two parts2 in the
 first there is a general  account of   
magnetism and the properties of the     
loadstone1 closing with a  discussion of
 the inquiry whence the magnet receives 
the natural virtue  which it has4 ,peter
 attributed this virtue to a sympathy   

with the  heavens1 proposing to prove   
his point by the construction of a      
terrella1 a uniform sphere of loadstone 
which is to be carefully  balanced and  
mounted in the manner of an armillary   
sphere1 with its axis  directed along   
the polar axis of the diurnal rotation4 
,he then  continues3      ,now if the   
stone then move according to the motion 
of the    heavens1 rejoice that you have
 arrived at a secret marvel4    ,but if 
not1 let it be ascribed rather to your  
own want of    skill than to a defect of
 ,nature4 ,but in this position1 or     
mode of placing1 ,i deem the virtues of 
this stone to be    properly conserved1 
and ,i believe that in other positions  
or parts of the sky its virtue is       
dulled1 rather than    preserved4 ,by   
means of this instrument at all events  
you    will be relieved from every kind 
of clock 7horologium71    for by it you 
will be able to know the ,ascendant at  
whatever hour you will1 and all other   
dispositions of the    heavens which    

,astrologers seek after4    ,it should  
be noted that the device is to be       
mounted like an astronomical  instrument
 and used like one1 rather than as a    
time teller1 or as a  simple            
demonstration of magnetism4 ,in the     
second part of the ,epistle  ,peter     
turns to practical instruments1         
describing for the first time1 the      
construction of a magnetic compass      
consisting of a loadstone or iron       
needle pivoted with a casing marked with
 a scale of degrees4 ,the third  chapter
 of this section1 concluding the        
,epistle1 then continues with  the      
description of a perpetual motion wheel1
 elaboured with marvellous  ingenuity1  
in the pursuit of which invention ,i    
have seen many people  wandering about1 
and wearied with manifold toil4 ,for    
they did not  observe that they could   
arrive at the mastery of this by means  
of the  virtue1 or power of this stone4 
,this tells us incidentally1 that the   
perpetual motion device was a  subject  

of considerable interest at this        
time4#db ,oddly enough1 ,peter  does not
 now develop his idea of the terrella1  
but proceeds to something  quite new1 a 
device 7see fig4 #bb7 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 teeth1 the teeth being there 
not to mesh  with others but to draw the
 magnet from one to the next1 a little  
bead  providing a counterweight to help 
the inertia of rotation carry the       
magnet from one point of attraction to  
the next4 ,it is by no means the  sort  
of device that one would naturally      
evolve as a means of making  magnetism  
work perpetually1 and ,i suggest that   
the toothed wheel is  another instance  
of some vague idea of protoclocks1      
perhaps that of ,su  ,sung1 being       
transmitted from the ,east4             
,illustration3 ,figure #bb4--,,magnetic 
,,perpetual ,,motion ,,wheel illustrated
  by ,peter ,peregrinus2 from the       

edition of ,s4 ,p4 ,thompson 7see       
footnote  #dj74    ,the work of ,peter  
,peregrinus is cited by ,roger ,bacon in
 his ,de  secretis as well as in the    
,opus majus and ,opus minus4 ,in the    
first  and earliest of these occurs a   
description1 taken from ,ptolemy1 of the
  construction of the 7observing7       
armillary sphere4 ,he says that this    
cannot be made to move naturally by any 
mathematical device1 but a  faithful and
 magnificent experimentor is straining  
to make one out of  such material1 and  
by such a device1 that it will revolve  
naturally with  the diurnal heavenly    
rotation4 ,he continues with the        
statement that  this possibility is also
 suggested by the fact that the motions 
of  comets1 of tides1 and of certain    
planets also follow that of the ,sun and
  of the heavens4 ,only in the ,opus    
minus1 where he repeats reference to    
this device1 does he finally reveal that
 it is to be made to work by  means of  
the loadstone4    ,the form of ,bacon's 

reference to ,peregrinus is strongly    
reminiscent of  the statement by        
,robertus ,anglicus1 already mentioned  
as an indication  of preoccupation with 
diurnally rotating wheels1 at a date    
7#abga7  remarkably close to that of the
 ,epistle 7#abfi7--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 him1 perhaps at the  ,university of
 ,paris--a natural place to which the   
itinerant ,peter might  communicate his 
findings4    ,the fundamental question  
here1 of course1 is whether the idea of 
an  automatic astronomical device was   
transmitted from ,arabic1 ,indian1 or   
,chinese sources1 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 heavens4 ,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'  
transmission4          ,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     
clock4 ,just as we have astronomical    
models  from the earliest times1 so we  
find knowledge of the loadstone and some
  of its properties4 ,then1 parallel to 
the development of protoclocks in       
,china throughout the middle ages1 we   
have the evidence analyzed by  ,needham1
 showing the use of the magnet as a     
divinatory device and of the            
7nonmagnetic7 south-pointing chariot1   
which has been confusedly allied  to the
 story4 ,curiously1 and perhaps         
significantly the ,chinese history      
comes to a head at just the same time   
for compasses and clocks1 and a  prime  
authority for the ,chinese compass is   
,shen ,kua 7#ajcj-ajic7 who also        
appears in connection with the clock of 
,su ,sung1 and who wrote about the      

mechanized armillary spheres and other  
models ca4 #ajhf4    ,another similarity
 occurs in connection with the history  
of the compass  in medieval ,europe4    
,the treatise of ,peter ,peregrinus1    
already discussed1  provides the first  
complete account of the magnetic compass
 with a  pivoted needle and a circular  
scale1 and this1 as we have seen1 may be
  connected with protoclocks and        
perpetual-motion devices4 ,there are    
several earlier references1 however1 to 
the use of the directive  properties of 
loadstone1 mainly for use in navigation1
 but these  earliest texts have a long  
history of erroneous interpretation     
which is  only recently being cleared   
away4 ,we know now that the famous      
passages  in the ,de naturis rerum and  
,de utensilibus of ,alexander           
,neckham#dc  7ca4 #aahg7 and a text by  
,hugues de ,berze#dd 7after ca4 #abjd7  
refer  to nothing more than a floating  
magnet without pivot or scale1 but using
  a pointer at right angles to the      

magnet1 so that it pointed to the east1 
rather than the north or south4 ,a      
similar method is described 7ca4  #abjj7
 in a poem by ,guyot de ,provins1 and in
 a history of ,jerusalem by  ,jacques de
 ,vitry 7#abae74de ,it is of the        
greatest interest that1 once  more1 all 
the evidence seems to be concentrated in
 ,france 7,neckham was  teaching in     
,paris7 though at an earlier period than
 that for the  protoclocks4    ,the date
 might suggest the time of the first    
great wave of transmissal  of learning  
from ,islam1 but it is clear that in    
this instance1 peculiar  for that       
reason1 that ,islam learned of the      
magnetic compass only after  it was     
already known in the ,west4 ,in the     
earliest ,persian record1 some          
anecdotes compiled by al-',awfi ca4     
#abcj1df the instrument used  by the    
captain during a storm at sea has the   
form of a piece of hollow  iron1 shaped 
like a fish and made to float on the    
water after  magnetization by rubbing   

with a loadstone2 the fishlike form is  
very  significant1 for this is          
distinctly ,chinese practice4 ,in a     
second ,muslim  reference1 that of      
,bailak al-,qabjaq 7ca4 #abhb71 the     
ordinary  wet-compass is termed         
al-konbas1 another indication that it   
was  foreign to that language and       
culture4#dg      ,chronological ,chart  
----------------------------------------
--------------------------------        
,,china      #dth ,c41 ,b4,c4 ,power    
gearing      ,,classical ,,europe       
#crd ,c41 ,b4,c4 ,archimedes planetarium
    #bnd ,c41 ,b4,c4 ,hipparchus        
,stereographic ,projection    #ast ,c41 
,b4,c4 ,vitruvius hodometer and water   
clocks    #fe1 ,b4,c4 7ca47 ,antikythera
 machine    #ast ,c41 ,a4,d4 ,hero      
hodometer and water clocks    #bnd ,c41 
,a4,d4 ,salzburg and ,vosges anaphoric  
clocks      ,,china      #bnd ,c41      
,a4,d4 ,chang ,hng animated globe       
hodometer        ,continuing tradition  
of animated astronomical models     #gbe

 ,invention of ,chinese escapement by   
,i-,hsing and ,liang ,ling-tsan         
,,islam       #hjg ,harun-al-,rashid    
#hej 7ca47 ,earliest extant astrolabes  
#ajjj ,geared astrolabe of al-,biruni   
,,europe      #ajjj ,gerbert            
astronomical model      ,,islam         
#ajbe ,equatorium text      ,,china     
#ajgd ,shen ,kua1 clocks and magnetic   
compass    #ajhj ,su ,sung clock built  
#aaja ,su ,sung clock destroyed         
,,india      #aajj 7ca47 ,srya ,siddhnta
 animated astronomical models           
and perpetual motion    #aaej 7ca47     
,siddhnta ,siromai animated models and  
perpetual            motion      ,,islam
      #aaej ,saladin clock      ,,europe
      #aahg ,neckham on compass    #aaih
 ,jocelin on water clock      ,,islam   
#abjj 7ca47 ,riwn water-clocks1         
perpetual motion            and weight  
drive    #abjf al-,jazar clocks1 etc4   
#abba ,geared astrolabe    #abcb        
,charlemagne clock    #abdc al-,konbas  
7compass7      ,,europe      #abde      

,villard clocktower1 escapement1        
perpetual motion    #abfg ,villers      
,abbey clock    #abfi ,peregrinus1      
compass and perpetual motion    #abga   
,robertus ,anglicus1 animated models and
 perpetual motion clock      ,,islam    
#abgb ,alfonsine corpus clock with      
mercury drum1 equatoria      ,,europe   
#abhe ,drover's water clock with wheel  
and weight drive    #acjj 7ca47 ,french 
geared astrolabe    #acbj ,richard of   
,wallingford astronomical clock and     
equatorium    #acfd de ,dondi's         
astronomical clock with mechanical      
escapement    later #adth ,c4 ,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 ,china1  though one     
cannot well admit that the first news of
 it was brought1 as  the legend states1 

by ,marco ,polo1 when he returned home  
in #abfj4 ,there  might well have been  
another wave of interest1 giving the    
impetus to  ,peter ,peregrinus at this  
time1 but an earlier transmission1      
perhaps  along the silk road or by      
travelers in crusades1 must be          
postulated to  account for the evidence 
in ,europe1 ca4 #abjj4 ,the earlier     
influx does  not play any great part in 
our main story2 it arrived in ,europe   
before  the transmission of astronomy   
from ,islam had got under way           
sufficiently  to make protoclocks a     
subject of interest4 ,for a second      
transmission1 we  have already seen how 
the relevant texts seem to cluster1 in  
,france  ca4 #abgj1 around a complex in 
which the protoclocks seem combined with
  the ideas of perpetual motion wheels  
and with new information about the      
magnetic compass4    ,the point of this 
paper is that such a complex exists1    
cutting across  the histories of the    
clock1 the various types of astronomical

 machines1  and the magnetic compass1   
and including the origin of self-moving 
wheels4 ,it seems to trace a path       
extending from ,china1 through ,india   
and through ,eastern and ,western       
,islam1 ending in ,europe in the ,middle
  ,ages4 ,this path is not a simple one1
 for the various elements make their    
appearances in different combinations   
from place to place1 sometimes one  may 
be dominant1 sometimes another may be   
absent4 ,only by treating it as  a whole
 has it been possible to produce the    
threads of continuity which  will1 ,i   
hope1 make further research possible1   
circumventing the blind  alleys found in
 the past and leading eventually to a   
complete  understanding of the first    
complicated scientific machines4        
,,footnotes3      #a ,this traditional  
view is expressed by almost every       
history    of horology4 ,an ultimate    
source for many of these has been the   
following two classic treatments3 ,j4   
,beckmann1 ,a history of    inventions  

and discoveries1 #dth ed41 ,london1     
#ahdf1 vol4 #a1 pp4    #cdj ff4 ,a4 ,p4 
,usher1 ,a history of mechanical        
inventions1 #bnd    ed41 ,harvard       
,university ,press4 #aied1 pp4 #aia ff41
 #cjd ff4      #b ,there is a           
considerable literature dealing with the
 later    evolution of perpetual motion 
devices4 ,the most comprehensive        
treatment is ,h4 ,dircks1 ,perpetuum    
mobile1 ,london1 #ahfa2 #bnd    ser41   
,london1 #ahgj4 ,so far as ,i know there
 has not previously    been much        
discussion of the history of such       
devices before the    renaissance4      
#c ,for the early history of gearing in 
the ,west see ,c4    ,matschoss1        
,geschichte des ,zahnrades1 ,berlin1    
#aidj4 ,also ,f4 ,m4    ,feldhaus1 ,die 
geschichtliche ,entwicklung des         
,zahnrades in    ,theorie und ,praxis1  
,berlin1 #aiaa4      #d ,a general      
account of these important              
archaeological objects    will be       
published by ,j4 ,needham1 ,science and 

civilisation in    ,china1 ,cambridge1  
#aiei7871 vol4 #d4 ,the original        
publications    7in ,chinese7 are as    
follows3 ,wang ,chen-to1 ,investigations
 and    reproduction in model form of   
the south-pointing carriage and         
hodometer1 ,national ,peiping ,academy  
,historical ,journal1    #aicg1 vol4 #c1
 p4 #a4 ,liu ,hsien-chou1 ,chinese      
inventions in    horological            
engineering1 ,ch'ing-,hua ,university   
,engineering    ,journal1 #aief1 vol4   
#d1 p4 #a4      #e ,for illustrations of
 intermeshing worms in ,indian cotton   
mills1 see ,matschoss1 op4 cit4         
7footnote #c71 figs4 #e1 #f1 #g1    p4  
#g4      #f ,it is interesting to note  
that the ,chinese hodometer was         
contemporary with that of ,hero and     
,vitruvius and very similar    in       
design4 ,there is no evidence whatsoever
 upon which to decide    whether there  
may have been a specific transmission of
 this    invention or even a stimulus   
diffusion4      #g ,a summary of the    

content of the manuscript sources1      
illustrated by the original drawings1   
has been published by ,h4    ,alan      
,lloyd1 ,giovanni de ,dondi's           
horological masterpiece1    #acfd1      
without date or imprint 78,lausanne1    
#aiee71 #bc pp4 ,it    should be        
remarked that de ,dondi declines to     
describe the    workings of his crown   
and foliot escapement 7though it is well
    illustrated7 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 clock4 ,but 
this may be bravado to quite a large    
degree4      #h ,see1 for example1 the  
chronological tables of the #adth       
century and the later mentions of clocks
 in ,e4 ,zinner1 ,aus der    ,frhzeit   
der ,rderuhr1 ,munich1 #aied1 p4 #bi ff4
 ,unfortunately    this very complete   
treatment tends to confuse the factual  
and    legendary sources prior to the   
clock of de ,dondi2 it also    accepts  

the very doubtful evidence of the       
escapement drawn by    ,villard of      
,honnecourt 7see p4 #ajg74 ,an excellent
 and fully    illustrated account of    
monumental astronomical clocks          
throughout the world is given by ,alfred
 ,ungerer1 ,les horloges                
astronomiques1 ,strasbourg1 #aica1 #ead 
pp4 ,available accounts of    the       
development of the planetarium since the
 middle ages are    very brief and      
especially weak on the early history3   
,helmut    ,werner1 ,from the ,aratus   
globe to the ,zeiss planetarium1        
,stuttgart1 #aieg2 ,c4 ,a4 ,crommelin1  
,planetaria1 a historical    survey1    
,antiquarian ,horology1 #aiee1 vol4 #a1 
pp4 #gj-ge4      #i ,derek ,j4 ,price1  
,clockwork before the clock1            
,horological    ,journal1 #aiee1 vol4   
#ig1 p4 #haj1 and #aief1 vol4 #ih1 p4   
#ca4      #aj ,for the use of this      
material ,i am indebted to my           
co-authors4 ,i must also acknowledge    
thanks to the ,cambridge    ,university 

,press1 which in the near future will be
 publishing    our monograph1 ,heavenly 
,clockwork4 ,some of the findings of    
this paper are included in shorter form 
as background material    for that      
monograph4 ,a brief account of the      
discovery of this    material has been  
published by ,j4 ,needham1 ,wang ,ling1 
and ,derek    ,j4 ,price1 ,chinese      
astronomical clockwork1 ,nature1 #aief1 
vol4 #agg1 pp4 #fjj-fjb4      #aa ,for  
these translations from classical       
authors ,i am    indebted to ,professor 
,loren ,mac,kinney and ,miss ,harriet   
,lattin1    who had collected them for a
 history1 now abandoned1 of             
planetariums4 ,i am grateful for the    
opportunity of giving them    here the  
mention they deserve4      #ab ,a4 ,g4  
,drachmann1 ,the plane astrolabe and the
 anaphoric    clock1 ,centaurus1 #aied1 
vol4 #c1 pp4 #ahc-ahi4      #ac ,a      
fuller description of the anaphoric     
clock and cognate    water-clocks is    
given by ,a4 ,g4 ,drachmann1 ,ktesibios1

 ,philon    and ,heron1 ,acta ,historica
 ,scientiarum ,naturalium et            
,medicinalium1 ,copenhagen1 #aidh1 vol4 
#d4      #ad ,first published by ,o4    
,benndorf1 ,e4 ,weiss1 and ,a4 ,rehm1   
,jahreshefte des sterreichischen        
archologischen ,institut in    ,wien1   
#aijc1 vol4 #f1 pp4 #cb-di4 ,i have     
given further details of    its         
construction in ,a history of           
technology1 ed4 ,singer1    ,holmyard1  
and ,hall1 #aieg1 vol4 #c1 pp4 #fjd-fje4
      #ae ,l4 ,maxe-,werly1 ,mmoires de 
la ,socit ,nationale des    ,antiquaires
 de ,france1 #ahhg1 vol4 #dh1 pp4       
#agj-agh4      #af ,the first definitive
 account of the ,antikythera machine    
was given by ,perikles ,rediadis in ,j4 
,svoronos1 ,das ,athener                
,nationalmuseum1 ,athens1 #aijh1        
,textband ,i1 pp4 #dc-ea4 ,since        
then1 other photographs 7mostly very    
poor7 have appeared1 and    an attempt  
at a reconstruction has been made by    
,rear ,admiral    ,jean ,theophanidis1  

,praktika tes ,akademias ,athenon1      
,athens1    #aicd1 vol4 #i1 pp4 #adj-adi
 7in ,french74 ,i am deeply grateful to 
the ,director of the ,athens ,national  
,museum1 ,m4 ,karouzos1 for    providing
 me with an excellent new set of photos1
 from which    figures #f-h are now     
taken4      #ag ,h4 ,diels ber die von  
,prokop beschriebene ,kunstuhr von      
,gaza1 ,abhandlungen1 ,akademie der     
,wissenschaften1 ,berlin1               
,philos4-,hist4 ,klasse1 #aiag1 ,no4 #g4
      #ah ,l4 ,a4 ,mayer1 ,islamic      
astrolabists and their works1           
,geneva1 #aief1 p4 #fb4      #ai ,the   
translation which follows is quoted from
 ,j4 ,beckmann1    op4 cit4 7footnote   
#a71 p4 #cdi4      #bj ,e4 ,wiedemann1  
,ein ,instrument das die ,bewegung von  
,sonne    und ,mond darstellt1 nach al  
,biruni1 ,der ,islam1 #aiac1 vol4 #d1   
p4 #e4      #ba ,i acknowledge with     
thanks to the ,curator of that museum   
the permission to reproduce photographs 
of this instrument4 ,it    is item #e in

 ,r4 ,t4 ,gunther1 ,astrolabes of the   
world1 ,oxford1    #aicb4      #bb      
,abulcacim ,abnacahm1 ,libros del saber1
 edition by ,rico y    ,sinobas1        
,madrid1 #ahff1 vol4 #c1 pp4 #bda-bga4  
,the design of the    instrument has    
been very fully discussed by ,a4        
,wegener1 ,die    astronomischen ,werke 
,alfons ,x1 ,bibliotheca ,mathematica1  
#aije1 pp4 #abi-ahi4 ,a more complete   
discussion of the historical            
evolution of the equatorium is given in 
,derek ,j4 ,price1 ,the    equatorie of 
the planetis1 ,cambridge 7,eng471 #aiee1
 pp4    #aai-acc4      #bc ,e4          
,wiedemann1 and ,f4 ,hauser1 ber die    
,uhren im ,bereich d4    islamischen    
,kultur1 ,nova ,acta2 ,abhandlungen der 
knigliche                               
,leopoldinisch-,carolinische ,deutsche  
,akademie der ,naturforscher    zu      
,halle1 #aiae1 vol4 #ajj1 no4 #e4       
#bd ,e4 ,wiedemann1 and ,f4 ,hauser1    
,die ,uhr des ,archimedes und    zwei   
andere ,vorrichtungen1 ,halle1 #aiah4   

#be ,the manuscripts in question are as 
follows3 ,gotha1 ,kat4 v4    ,pertsch4  
#c1 #ah1 no4 #acdh2 ,oxford1 ,cod4 #ied2
 ,leiden1 ,kat4 #c1    #bhh1 no4 #adad1 
,cod4 #dii ,warn2 and another similar1  
,kat4 #c1 #bia1    no4 #adae1 ,cod4 #ic 
,gol4      #bf ,h4 ,schmeller1 ,beitrge 
zur ,geschichte der ,technik in der     
,antike und bei den ,arabern1 ,erlangen1
 #aibb 7,abhandlungen zur    ,geschichte
 der ,naturwissenschaften und der       
,medizin no4 #f74      #bg ,once more ,i
 am indebted to ,professor ,loren       
,mac,kinney and    ,miss ,harriet       
,lattin 7see footnote #aa7 for making   
their    collections on ,gerbert        
available to me4      #bh ,item #aih in 
,gunther1 op4 cit4 7footnote #ba74 ,i am
    grateful to the authorities of that 
museum for permission to    reproduce   
photographs of this instrument4      #bi
 ,sotheby and ,co41 ,london1 sale of    
,march #ad1 #aieg1 lot #aed4    ,the    
outer rim of the rete has #abj teeth4   
#cj ,the ,latin text of the treatise on 

the ,albion1 has been    transcribed by 
,rev4 ,h4 ,salter and published in ,r4  
,t4 ,gunther1    ,early science in      
,oxford1 ,oxford1 #aibc1 vol4 #b1 pp4   
#cdi-cgj4    ,an analysis of its design 
is given in ,price1 op4 cit4            
7footnote #bb71 pp4 #abg-acj4      #ca  
,such evidence as there is for the      
existence and form of    the clock is   
collected by ,gunther1 op4 cit4         
7footnote #cj71 p4    #di4      #cb ,i  
have discussed this new manuscript      
source in ,two    medieval texts on     
astronomical clocks1 ,antiquarian       
,horology1    #aief1 vol4 #a1 no4 #aj1  
p4 #aef4 ,the manuscript in question is 
ms4    #bcj_/aaf1 ,gonville and ,caius  
,college1 ,cambridge1 folios    #aa-ad  
pp4 #ca-cf4      #cc ,the ,chronicle of 
,jocelin of ,brakelond 4441 ,h4 ,e4     
,butler    7ed471 ,london1 #aidi1 p4    
#ajf4      #cd ,c4 ,b4 ,drover1 ,a      
medieval monastic water-clock1          
,antiquarian ,horology1 #aied1 vol4 #a1 
no4 #e1 pp4 #ed-eh1 #fc4    ,because    

this water clock uses wheels and strikes
 bells one must    reject the evidence  
of literary reference1 such as by       
,dante1    from which the mention of    
wheels and bells have been taken as     
positive proof of the existence of      
mechanical clocks with    mechanical    
escapements4 ,the to-and-fro motion of  
the mechanical    clock escapement is   
quite an impressive feature1 but there  
seems to be no literary reference to it 
before the time of de    ,dondi4        
#ce ,annales de la ,socit ,royale       
d',archologie de ,bruxelles1    #ahif1  
vol4 #a_/h1 pp4 #bjc-bae1 #djd-dea4 ,the
 translation here is    cited from      
,drover1 op4 cit41 7footnote #cd71 p4   
#ef4      #cf ,l4 ,thorndike1 ,the      
sphere of ,sacrobosco and its           
commentators1 ,chicago1 #aidi1 pp4 #ahj1
 #bcj4      #cg ,the album was published
 with facsimiles by ,j4 ,b4 ,a4         
,lassus1 #aheh4 ,an ,english edition    
with facsimiles of #cc of the    #da    
folios was published by ,rev4 ,robert   

,willis1 ,oxford1 #ahei4 ,an            
extensive summary of this section is    
given1 with illustrations1    by ,j4    
,drummond ,robertson1 ,the evolution of 
clockwork1 ,london1    #aica1 pp4       
#aa-ae4      #ch ,m4 ,jules ,quicherat1 
,revue ,archologique1 #ahdi1 vol4 #f4   
#ci ,m4 ,c4 ,frmont4 ,origine de        
l'horloge  poids1 ,paris1    #aiae4     
#dj ,for this1 ,i have used and quoted  
from the very beautiful    edition in   
,english1 prepared by ,silvanus ,p4     
,thompson1 ,london1    ,chiswick ,press1
 #aijb4      #da ,see ,e4 ,g4 ,r4       
,taylor1 ,the ,south-pointing needle1   
,imago    ,mundi1 ,leiden1 #aiea1 vol4  
#h1 pp4 #a-g 7especially pp4 #a1 #b74   
#db ,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    
,friday4 ,unfortunately ,i can find no  
evidence for or against the             
conjecture4      #dc ,w4 ,e4 ,may1      

,alexander ,neckham and the pivoted     
compass    needle1 ,journal of the      
,institute of ,navigation1 #aiee1 vol4  
#h1 no4 #c1 pp4 #bhc-bhd4      #dd ,w4  
,e4 ,may1 ,hugues de ,berze and the     
mariner's compass1    ,the ,mariner's   
,mirror1 #aiec1 vol4 #ci1 no4 #b1 pp4   
#ajc-ajf4      #de ,h4 ,balmer1 ,beitrge
 zur ,geschichte der ,erkenntnis des    
,erdmagnetismus1 ,aarau1 #aief1 p4 #eb4 
#df ,the collection is the ,gami 'al    
,hikajat2 the relevant    passage being 
given in ,german translation in ,balmer4
 op4 cit4    7footnote #de71 p4 #ed4    
#dg ,balmer1 op4 cit4 7footnote #de71 p4
 #ec4        ,u4,s4 ,,government        
,,printing ,,office3 #aiei