452 LECTURE XLVIII. 



sufficiently accurate to be employed in astronomical calculations, are those 

 made at Babylon in the years 71 9 and 720 before the Christian era, of three 

 eclipses of the moon. Ptolemy,* who has transmitted them to us, employed 

 them for determining the period of the moon's mean motion, and, therefore, 

 had probably none more ancient on which he could depend. The Chal- 

 deans, t however, must have made a long series of observations before they 

 could discover their Saros or lunar period of 6585^ days, or about 18 years, 

 in which (as they had learnt at a very early time) the place of the moon, 

 her node and apogee return nearly to the same situation with respect to 

 the earth and sun ; and of course a series of nearly similar eclipses recurs. 

 The observations attributed to Hermes indicate a date seven hundred years 

 earlier than those of the Babylonians, but their authenticity appears to be 

 extremely doubtful. 



The Egyptians J were very early acquainted with the length of the year, 

 as consisting nearly of 365 days and a quarter, and they derived from it 

 their Sothic period of 1460 years, containing 365 days each. The accurate 

 correspondence of the faces of their pyramids with the points of the compass 

 is considered as a proof of the precision of their observations : but their 

 greatest merit was the discovery that Mercury and Venus revolve round 

 the sun, and not round the earth, as it had probably been before believed :|| 

 they did not, however, suppose the same of the superior planets. (Plate 

 XXXVIII. Fig. 525, 526.) 



In Persia and in India, the origin of astronomy is lost in the darkness 

 which envelopes the early history of those countries. We find the annals 

 of no country so ancient and so well authenticated as those of China, which 

 are confirmed by an incontestable series of historical monuments. The 

 regulation of the calendar, and the prediction of eclipses, were regarded in 

 this country as important objects, for which a mathematical tribunal was 

 established at a very early period. But the scrupulous attachment of the 

 Chinese to their ancient customs, extending itself even to their astronomy, 

 has impeded its progress, and retained it in a state of infancy. The Indian 

 tables indicate a much higher degree of perfection in the early state of the 

 science than it had attained in China ; but we have every reason to believe 

 that they are not of very remote antiquity. " Here," says Mr. Laplace, IT 

 who must be allowed to be free from prejudices in favour of established 

 opinions, " I am sorry to be obliged to differ from an illustrious philoso- 

 pher, Mr. Bailly, who, after having distinguished his career by a variety of 

 labours useful to the sciences, and to mankind at large, fell a victim to the 

 most sanguinary tyranny that ever disgraced a civilised nation. The 

 Indian tables are referred to two principal epochs, which are placed the 

 one 3102 years before Christ, the other 1491. These are connected by the 

 mean motions, and not the true motions, of the sun, the moon, and the 

 planets ; so that one of the epochs must necessarily be fabulous. The cele- 



.* Ptol. Almagest. 1. 4, c. 6. 



t Suidas, Lexicon (Saros). Pliny, Hist. Nat. 1. 2, c. 13. 



J Giraud, Journal des Savans, 1760. 



Mem. del'Acad. 1710. c 



|| Macrobius, Comm. in Somn. Scip. 1.1, c. 9. 



f Exposition du Systeme du Monde, 2nd edit. p. 239. 



