From ihc adjacent region there is 

 another account of a striking water 

 clock, the evidence lieing inscriptions 

 on slates, discovered in \illers Abbey 

 near Brussels; ^' these may be closely 

 dated as 1267 or 1268 and proxide the 

 remains of a memorandum for the sacrist 

 and his assistants in charge of the clock. 



Always set the clock, however long yoii 

 may delay on [the letter "A"] afterwards 

 you shall pour water from the little pot 

 (pottulo) that is there, into the reservoir 

 (cacabum) until it reaches the prescribed 

 level, and you must do the same when you 

 set [the clock] after compline so that you 

 may sleep soundly. 



A quite different sort of evidence is to 

 be had from the writings of Robertiis 

 Anglicus in 1271 where one gets the 

 impression that just at this time there 

 was active interest in the attempt to 

 make a weight-driven anaphoric clock 

 and to regulate its motion ijy some 

 unstated method so that it would keep 

 time with the diurnal rotation of the 

 heavens: ^^ 



Nor it is possible for any clock to follow the 

 judgment of astronomy with complete accu- 

 racy. Yet clockmakers (artifices horol- 

 ogiorum) are trying to make a wheel (cir- 

 culum) which will make one complete revoluiion for every 

 one of the equinoctial circle, but tlicy cannot quite perfect 

 their work. But if they could, it would be a really accurate 

 clock (horologium verax valde) and worth more than an 

 astrolabe or other astronomical instrument for reckoning 

 the hours, if one knew how to do this according to the 

 method aforesaid. The method of making such a clock 

 would be this, that a man make a disc (circulum) of uniform 

 weight in every part so far as could possibly be done. 

 Then a lead weight should be hung from the a.\is of that 

 wheel (a.xi ipsius rote) and this weight would move that 

 wheel so that it would complete one revolution from sunrise 

 to sunrise, minus as much time as about one degree rises 

 according to an approximately correct estimate. For from 

 sunrise to sunrise, the whole equinoctial rises, and about 

 one degree more, through which degree the sun moves 

 against the motion of the firmament in the course of a 



"Annales de la Societe Rotale (T Archeologie de BruxdUs, 1896, 

 vol. 1/8, pp. 203-215, 404-451. The translation here is cited 

 from Drover, op. cit., (footnote 34), p. 56. 



" L. Thorndikc, The sfiheie of Sacrobosco and its commentators, 

 Chicago, 1949, pp. 180, 230. 



Figure ig. — Manuscript Illumination of a Mi.di- 

 EVAL VVatkrclock, showing a partitioned wheel, a 

 weight drive, and a carillion for striking. From 

 Drover (see footnote 34). 



natural day. Moreover, this could be done more accurately 

 if an astrolablc were constructed with a network on which 

 the entire equinoctial circle was divided up. 



The text then cimlinues witli technical astronomical 

 details of the slight difference between the rate of 

 rotation of the sun and of the fixed stars (because of 

 the annual rotation of the sun amongst the stars) 

 but it gives no indication of any regulatory device. 

 Again it should be noted, this source comes from 

 France; Robertus, though of English origin, ap- 

 parently being then a lecturer either at the I'niversity 

 of Paris or at that of Montpcllier. The date of this 

 pas.sage, 1271, has been taken as a terminus post quern 

 for the invention of the mechanical clock. In the 

 next section we shall describe the text of Peter Pere- 

 grinus, very close to this in place and date, which 

 describes just such a machine, conflating it with 

 accounts of an armillary sphere, perpetual motion, 

 and the magnetic compass — so bringing all these 

 threads together for the fust time in Europe. 



106 



BULLETIN 218: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



