phoric clock, the wcitjlu clrixc, and a most curious 

 pcrpclual-motion dfvice, the mercury wheel, used as 

 an escapement or regulator. The Alfonsine book on 

 clocks contains descriptions of five devices in all, four 

 of them being due to Isaac b. Sid (two sundials, an 

 automaton water-clock and the present mercury 

 clock) and one to Samuel ha-Levi Adulafia (a candle 

 clock) — they were probably comixjsed just before 

 ca. 1276-77. 



The niercur\- clock of Isaac b. Sid consists of an 

 aslroialjc dial, rotated as in the anaphoric clock, and 

 fitted with 30 leaf-shaped gear teeth (see fie;. 13). 



perpetual-motion devices found in the medieval 

 European tradition and also in the texts associated 

 with Ridwan, which we shall next examine. 



It is of the greatest interest to our theme that the 

 Islamic contributions to horoloi^y and perpetual 

 motion seem to form a closely knit corpus. A most 

 important series of horological texts, including those 

 of Ridwan and al-Jazari, have licen edited by Wiede- 

 mann and Hauser.-^ Other Islamic texts give versions 

 of the water clocks and automata of Archimedes and 

 of Hero and Philo of .Mexandria.-* In at least three 

 cases -■' these texts are found also associated with texts 



Figure 14. — Islamic Perpetial Motion Wheel, 

 after manuscript cited by Schmcllcr (see footnote 26). 



Figure 15. — Another Peri'etual Motion Wheel, 

 after the text cited in figure 14. 



These are dri\-en by a ])ini()n off) leaves mounted on a 

 horizontal axle (shown ver>- diagrammaticalh in the 

 illustration) and at the other end of this axle is a 

 wheel on which is mounted the special mercury 

 drum which is powered i>\' a normal weight drive. 



It is the mercury drum which forms the most novel 

 feature of this device; the fluid, constrained in 12 

 chambers so as to just fill 6 of them, must slowly filter 

 through stnall holes in the constraining walls. In 

 practice, of course, the top mercury surfaces will not 

 be level, but hiti;her on the right so as to balance 

 dynamically the moment of the applied weight on its 

 driven rope. This curious arrannemeni shows point 

 of resemblance to the Indian "mercury-holes," to the 



describing perpetual-motion w-heels and other hy- 

 draulic devices. Three manuscripts of this type have 

 been [juljlished in German translation by Schmeller.'* 



-' E. Wiedemann, and F. Hauscr, "Ubcr die Uhrcn im 

 Bcrcich d. islamischcn Kultur," jVova Ada; Aihandhngm der 

 konigliclu Lropoldinisch-CaroUnischt Dnilschr Akademie der \aliir- 

 (orscher zu Halle, 1915, vol. 100, no. 5. 



-* E. Wiedemann, and F. Haiiscr, Die Uhr des Archimedes und 

 Ztvei andere Vorrichtungrn, Halle, 1918. 



-5 The manuscript!! in question are as follows: Gotha, Kat. v, 

 Pertsch. 3, 18, no. 1348: Oxford. Cod. 954: Leiden, Kal. 3, 288, 

 no. 1414, Cod. 499 Warn; and another similar, Kat. 3, 291, no. 

 1415, Cod. 93Gol. 



" H. Schmeller. Beitrat;e zur Geschichtc der Tcchnik in der 

 .\ntike und bci den .Vabern, Erlangen, 1 922 (Abhandlungen zur 

 Geschichte der Nalurwissenschajltn und drr .\tedizin no, 6). 



P.\PER 6: CLOCKWORK, I'ERPETLAL MOTION DEVICES, .AND THE COMPASS 



101 



