]84l.] Description of a Persian Astrolabe. 765 



learned Hyde, who gives a Latin version of Ulug Beg's tables, which was 

 obligingly lent to me by our worthy Secretary, in his able preface to that 

 work, says of the author, " Inter distractiones animi et repetita regni 

 negotia administranda ad subtiliora in scientiis investiganda se appli- 

 cuit." And again quoting a contemporary historian and panegyrist, 

 he says, " At celsus iste animus etsi in summo rerum fastigio esset 

 constitutus tamen in pulverem mathematicum descendere non dedig- 

 natus esset." This historian, obviously, did not understand that the 

 royal astronomer while thus engaged, was but drawing pleasure from 

 its purest source, and inscribing his name on the bright heavens, in a 

 character which would not soon be forgotten. We are informed by 

 Ulug Beg himself, that for the observations, the result of which appear 

 in his tables, he caused to be constructed a quadrant of great radius, 

 " cujus radius altitudine Templi Sanctae Sophise sequaret," and that the 

 latitudes and longitudes of the stars thus obtained, were to serve as 

 data for future computations, the method of effecting which, he himself 

 supplies. 



" Stellarum loca in tabulis designavimus pro initio anno Hejyra 841, 

 at quovis tempore quis possit stellarum loca invenire cum singulis sep- 

 tuagenis annis solaribus per annum tantum gradum moveantur." The 

 addition of 1° for every 70 years is not quite correct, as the precession 

 of the equinoxes is about 1° in 72 years nearly, on the average, since 

 the time of Ulug Beg; at present it is 1° in 71.66 years. Allowance 

 is also to be made for the diminution of the obliquity, a fact which 

 appears to have been unknown to ancient astronomers. 



