EARLY CATALOGUES. 149 



Although the so-called Ptolemaic catalogue of the fixed 

 stars enumerated only one-fourth of those visible to the 

 naked eye at Rhodes and Alexandria, and, owing to erroneous 

 reductions of the precession of the equinoxes, determined their 

 positions as if they had been observed in the year 63 of our 

 era ; yet, throughout the sixteen hundred years immediately 

 following this period, we have only three original catalogues 

 of stars, perfect for their time; that of Ulugh Beg (1437), that 

 of Tycho Brahe (1600), and that of Hevelius (1660). During 

 the short intervals of repose which, amid tumultuous revolu- 

 tions and devastations of war, occurred between the ninth and 

 fifteenth centuries, practical astronomy, under Arabs, Persians, 

 p.nd Moguls (from Al-Mamun, the son of the great Harun Al- 

 Raschid, to the Timurite, Mohammed Taraghi Ulugh Beg, the 

 son of Shah Rokh) attained an eminence till then unknown. 

 The astronomical tables of Ebn-Junis (1007), called the Hake- 

 initic tables, in honour of the Fatimite Calif, Aziz Ben-Hakem 

 Biamrilla, afford evidence, as do also the Ilkhanic tables 12 of 

 Nassir-Eddin Tusi (who founded the great observatory at 

 Meragha, near Tauris, 1259), of the advanced knowledge of 

 the planetary motions, the improved condition of measuring 

 instruments, and the multiplication of more accurate methods 

 differing from those employed by Ptolemy. In addition to 

 clepsydras,* pendulum-oscillations 13 were already at this period 

 employed in the measurement of time. 



2 Cosmos, pp. 594-5. The Paris Library contains a 

 manuscript of the Ilkhanic Tables by the hand, of the son of 

 Nassir-Eddin. They derive their name from the title " Ilkhan," 

 assumed by the Tartar princes who held rule in Persia. 

 Reinaud, Introd. de la Geogr. d Aboul/eda, 1848, p. cxxxix. 



* For an account of clepsydras, see Beckmanns Inventions, 

 Tol. i. 341, et seq. (Bonn's edition.) Ed. 



13 Sedillot fils, ProUyomenes des Tables Astr. d' Oloug-Beg, 

 1847, p. cxxxiv. note 2. Delambre, Hist, del Astr. du moyen 

 Age, p. 8. 



