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to lis in the archaic Castilian of the Alfonsinc Libros 

 del saber." The sectifjns of this booi\. dealing with the 

 Laminas de las I'll I'latuias. describe not (jnly this 

 inslriinienl but also the inijiroved modification intro- 

 duced by Azarchicl (born ca. 1029, died ca. 1087). 



Xo Islamic examples of the equatorium have sur- 

 \i\ed, but iVom this period onward, there appears to 



Figure 13. — .'\stroi..'\be Clock, Regulated by a 

 Mercury Drum, from the Alfonsine Libros del saber 

 (see footnote 22). 



/ 



much easier to mark out "jt'ometrically {e.g., 10, 

 48, 60, and 64 teeth). The lunar phase volvelle can 

 be seen through the circular o))ening at the Ijack of 

 the astrolabe. It is quite certain that no automatic 

 action is intended: when the central pivot is turned, 

 by hand, probably l)y using the astrolabe rete as a 

 "handle," the calendrical circles and the lunar phase 

 are moved accordingly. Using one turn for a day 

 would be too slow for useful re-setting of the instru- 

 ment, in practice a turn corresponds more nearly to 

 an interval of one week. 



In addition to this geared development of the 

 astrolabe, the same period in Islam brought forth a 

 new device, the equatorium, a mechanical model 

 designed to simulate the geometrical constructions 

 used for finding the positions of the planets in Ptole- 

 maic astronomy. The method may have originated 

 already in classical times, a simple device being 

 described by Proclus Diadochus {ca. 450), but the 

 first general, though crude, planetary equatorium 

 seems to have been de.scribed by Abulcacim Abna- 

 cahm {ca. 1025) in Granada; it has been handed down 



ha\e been a long and active tradition of them, and 

 ultimately they were transmitted to the West, along 

 with the rest of the Alfonsine corpus. More important 

 for our argument is that they were the basis for the 

 mechanized astronomical models of Richard of 

 W'allingford (<y;. 1320) and probably others, and for 

 the already mentioned great astronomical clock of 

 de Dondi. In fact, the complicated gearwork and 

 dials of de Dondi's clock constitute a series of equa- 

 toria, mechanized in just the same way as the calen- 

 drical device described by Binmi. 



It is evident that we are coming nearer now to the 

 beginning of the true mechanical clock, and our last 

 step, also from the Alfonsine corpus of western Islam, 

 provides us with an important link between the ana- 



-- Abulcacim Abnacahm, Libros del saber, edition by Rico y 

 Sinobas, Madrid, 1866, vol. 3, pp. 241-271. The design of 

 the instrument has been very fully discussed by A. Wegener, 

 "Die astronomischen Werke Alfons X," Bibliolheea .\tathe- 

 mnlica, 1905, pp. 129-189. A more complete discussion of the 

 historical evolution of the equatorium is given in Derek J. Price, 

 The rqunlnrii- of Ihr platutis, Cambridge (Eng.), 1955, pp. 1 19-133. 



100 



BULLETIN 218: CONTRIBUTIONS FROM IHF MUSEUM OF HISIORY AND TECHNOLOGY 



