A S T 



at Pelufium in Egypt, in the beginning of the fecond cen- 

 tury of Chrilliamty, and was tlie firfl who midcitook to 

 reform the whole of this fcieiu-e, by eilabhtliiiig it upon a 

 new found:ition. In this enterprife, the fyftem he formed 

 is no-.v well known to be erroneous; but the edifice he 

 eriAed laded near 1400 years; and even at this t\w(, 

 though it is entirely deflroyed, his Almageft, confider.-d 

 as the depo(itoi-y of ancient obfen-ations, is one of the moft 

 precious monuments of antiquity. See Almagest. 



One of the molt impoitant difcoveries of this aflronomer 

 is that of the evcttion of the moon (fee Evection), which 

 he has affigned with fo much exaclnefs, that M. Le Place, 

 in oppufition to the opi.iion of other writers, thinks it 

 fufficient to entitle him to the character of an accurate 

 obfcrver; and that the chartfc which hns been made againft 

 him, of appropriating the difcoveries of his predeceflbrs, 

 is not well founded. 



It may alfo be remarked, that Ptolemy has rendered great 

 fervices to geography, by collecting all the determinations 

 of the latitudes and longitudes of places then known ; and 

 by his laying the foundation of the method of projeftions, 

 for the conftiuClion of geographical charts, which was but 

 little known before his time. In fliort, the various works 

 which he executed, upon a variety of fubjefts, are.ftrong 

 proofs of a great and enlightened mind, and will always 

 infiirc him a diilinguilhed rank in the hillory of the fciencts. 



With the labours of this great aftronomcr ended the 

 glory of the Alexandrian fchool, which had now fubfiftcd 

 for more than five centuries, with as much credit to itfclf 

 as advantage to the fciences; but the fucceflbrs of Hippar- 

 chus and Ptolem)', contented themfelves with commenting 

 on their works, without adding any thing remarkable to their 

 difcoveries. The knowledge of nature, which had hitherto 

 been cultivated with fo much luccefs, gave way to the 

 defolatiiig irruption of the Saracens, who were led by a fero- 

 cious zeal to dcftroy the celebrated library of Alexandria, 

 which contained fo many treafures of learning and genius. 

 By a fingular turn, however, of human affairs, this people 

 became afterwards the protedtors and cultivators of literature 

 and fcience, and were then fcnfible, that this frantic meafure 

 had deprived them of themoll precious fruits of their 

 iriiSlories. 



The caliph Almanfor firft introduced a tafte for the 

 fciences into his empire; and his grandfon, Almamon, who 

 afcended the throne in 813, was a great encourager and im- 

 prover of' allronomy. Having conftrudtcd proper inftru- 

 inents, he made many accurate obfervations; and, among 

 others, determined the obliquity of the ecliptic to be 23" 

 35'. Under his aufpices alfo, a degree of the meridian was 

 meafured, a fecond time, in the plains of Singar, on the 

 borders of the Red Sea. About the fame time, or at a fom.e- 

 wiiat later period, Alfragarius likewife wrote a treatife on 

 allronomy ; and hence the fcience began to be greatly cultiva- 

 ted by the Arabians; particularly by Albategniiis, who gave 

 a new and improved theory of the fun, from which he derived 

 refults that are much valued for their accuracy ; and above all, 

 as'heydircflly confirm the diminution of the eccentricity of the 

 folar orbit, as fince demon ftrated by the theory of gravity, 

 and by the fecular equation of the. moon. His work, in- 

 titled " The Science of the Stars," is itill extant, and was 

 long efteemed by the Arabians. But after his time, though 

 the Saracens had many eminent ailronomcrs, feveral cen- 

 turies elapfed withont producing any very valuable obferva- 

 tions, excepting thofe of fome eclipfes, obferved by Ibn 

 Junis, allronomer to the cahph of Egypt, which ferve to 

 fliew the acceleration of the mean motion of the moon. 



The Perfians, who for a long time were of the fame reli- 



AST 



gion, and fubjefted to the fame fovereigns with the Arabj, 

 began about the middle of the eleve.ith century, to tli'-ow 

 off the yoke of the caliphs; and at this period, their ca'endar 

 received, by the care of their aftronomcr, Omar Chcyam, a 

 new form, founded upon an ir^genious intercalation, which 

 confiftt-d in making eight bifR-xtile years at tlie end of every 

 thirty-three common years. See Bissextile. About the 

 fame time, alfo, Holagu llc^ouk;ui, one of their fovereigns, 

 aflembled the moft confiderable aftronomers at Maragha, 

 where he coiiftr.itted a magnificent obfcrvatory, the care 

 of which was confided to Nafilr-Eddin. But of all the 

 princes of this nation, the one who diftmguifhed himfelf the 

 moft, by his zeal for aftronomy, was Ulugh B.-tgh, a grand- 

 fon of the celebrated Tamerlane, who was a great proficient 

 in this fcience. ' He formed, from his own obltrvations, 

 at Samarcand, the cnpi'al of his empire, a new catalogue 

 of the ftars, and the bell tables of the fun and planets that 

 had been given before thole of Tycho Brahe. He alfo 

 determined, in 1437, with a quadrant 180 feet high, the 

 obliquity of the ecliptic, which he found equal to 23° 31' 



57"- . • . 



During this period, the greateft part of Europe was 

 immerfed in ignorance and barbarity; which would have 

 probably continued much longer, but for the fettlement of 

 the Moors in Spain, who firft introduced a tafte for literature 

 and the fciences into this part of the world. The Arabs 

 by this means became our inftrudtors, as the Egyptians had 

 been formerly of the Greeks; and, by a fingular fatality, 

 the learning which they tranfmitted to us, has difappeared 

 among this peop'e, as allronomy became ncglefted in the 

 temples of Egypt andChaldaea, in proportion to the progrefs 

 which it made in the fchool of Alexandria. 



One of the firft encouragers of learning in Europe was 

 Frederick II., who, about 1230, fet about rcftoring fome 

 decayed univedlties, and founding a new one at Vienna. 

 He alfo cauled the works of Ariftotle and Ptolen y'i Al- 

 mageft, to be tranflated into Latin ; from which latter cir- 

 ciimftance we may date the revival of allronomy in Europe. 

 Two years after this, John of Halifax, commonly knowa 

 by the name of Sacro Bofco, compiled from Ptolemy, AI- 

 bategnius, Alfraganus, and other Arabic aftronomers, his 

 work " De Sphxra," which continued in great eftimatioa 

 for more than 300 years afterwards, and was honoured 

 with commentaries by Clavius and other learned men. Al- 

 phonftfs. king of Caftile, may alfo be reckoned as one of 

 the moft zealous encouragers and proteftors of this fcience ; 

 though, being but ill fecondedbythe aftronomers of that time, 

 the tables which he publilhtd were not found to anfwer the 

 great cxpence which attended them. 



About the fame period alfo Roger Bacon, an Englidi 

 monk, befides many learned works of various kinds, wrote 

 feveral treatifes on aftronomy ; after which but little pro- 

 grefs was made in this fcience till the time of Purbach, 

 Regiomontanus, and Walther, who all flouriftied about 

 the end of the fifteenth century, and by their labours pre- 

 pared the way for the great d'fcoveries which followed. 

 Regiomontanus, in particular, who was born at Koning- 

 {berg, a town of Franconia, in 1436, and whofe proper 

 name v/as John Muller, rendered coufiderahle fervices to 

 aftronomy, not only by his obfervations and writings, but 

 by his trigonometrical tables of fines and tangents, which 

 he computed to a radius of i,ooo,oco for every minute of 

 the quadrant, and by this means greatly facilitated aftrono- 

 mica! computations, which had now become both nume- 

 rous and intricate. John Werner, who fucceeded Walther 

 as allronomer at Nureri:berg, is alfo deferving of notice, 

 as being the firil who propoicd the method of finding the 



longitude 



