head which rolled its eyes every hour on the hour, 

 exhibiting the time through lighted apertures and 

 showing mythological interpretations of the cosmos. 

 All these effects were produced by Heronic tech- 

 niques, using hydraulic power and puppets moved 

 by strings, rather than with gearing. 



Again in 807 a similarly marvelous exhibition 

 clock made of bronze was sent by Harun-al-Rashid 

 to the Emperor Charlemagne; it seems to have been 

 of the same type, with automata and hydraulic 

 works. For the succeeding few centuries, Islam 

 was in its Golden Age of development of technical 

 astronomy {ca. 950-1150) and attention may have 

 been concentrated on the more mathematical proto- 

 clocks. Towards the end of the 12th century, how- 

 ever, there was a revival of die old tradition, mainly at 

 the court of the Emperor Saladin (1146-1173) 

 when a great automaton water clock, more mag- 

 nificent than any hitherto, was erected in Damascus. 

 It was rebuilt, after 1168, by Muhammad b. 'Ali 

 b. Rustum, and repaired and improved by his son, 

 Fakhr ad-din Ridwan b. Muhammad,'* who is 

 most important as the author of a book which de- 

 scribes in considerable technical detail the construc- 

 tion of this and other protoclocks. Closely associated 

 with his book one also finds texts dealing with per- 

 petual-motion devices, which we shall consider later. 



During the century following this horological 

 exuberance in Damascus, the center of gravity of 

 Islamic astronomy shifted from the East to the 

 Hispano-Moorish West. At the same time there 

 comes more evidence that the line of mathematical 

 protoclocks had not been left unattended. This is 

 suggested by a description given by Trithemius of 

 another royal gift from East to \Vest which seems to 

 have been different from the automata and hydraulic 

 devices of the tradition from Procopius to Ridwan:'* 



In the same year [1232] the Saladin of Egypt sent by his 

 ambassadoi-s as a gift to the emperor Frederic a valuable 

 machine of wonderful construction worth more than five 

 thousand ducats. For it appeared to resemble internally 

 a celestial globe in which figures of the sun, moon, and 

 other planets formed with the greatest skill moved, being 

 impelled by weights and wheels, so that performing their 

 course in certain and fi.\ed intei-vals they pointed out the 

 hour night and day with infallible certainty; also the 

 twelve signs of the zodiac with certain appropriate char- 



" L. A. Mayer, Islamic aslrolabisls and their works, Geneva, 

 1956, p. 62. 



" The translation which follows is quoted from J. Bcckmann, 

 op. cit. (footnole 1), p. 349. 



Figure 10. — Calendrical Gearing Desic.ned by 

 AL-BiRUNi, ca. A. D. 1000. The gear train count is 

 40- 1 o + 7-59 + 1 9-59 -f- 24-48. The gear of 48 there- 

 fore makes ig (annual) rotations while that of 19-59 

 shows 118 double lunations of 29 + 30 = 59 days. 

 The gear of 40 shows a (lunar) rotation in exactly 

 28 days, and the center pinions 7+10 rotate in CNactly 

 one week. After W'iedemann (see footnote 20). 



acters, moved with the firmament, contained within them- 

 selves the course of the planets. 



The phrase "resembled internally"' is of especial 

 interest in this passage; it may perhaps arise as a 

 mistranslation of the technical term for stereographic 

 projection of the sphere, and if so the device might 

 have been an anaphoric clock or some other astrolabic 

 device. 



This is made more probable by the existence of a 

 specifically Islamic concentration on the astrolalx", 

 and on its planetary companion instriuncnt, the 

 equatorium, as devices for mechanizing computation 

 by use of geometrical analogues. The ordinar>' 

 planispheric astrolabe, of course, was known in 

 Islam from its first days until almost the present 

 time. From the time of al-Biruni {ca. 1000) — sig- 

 nificantly, perhaps, he b well known for his travel 

 account of India — there is remarkable innovation. 



Most cogent to our purixisc is a text, described for 

 the first time bv Wiedemann,-'" in which al-Biruni 



'" E. Wiedemann, "Ein Instrument das die Bewcgung von 

 Sonne und Mend darslellt, nach al Biruni," Dcr Islam, 1913, 

 vol. 4, p. 5. 



PAPER 6: CLOCKWORK, PERPETUAL MOTION DEVICES, AND THE COMP.\SS 



97 



