jgO LECTURE XLVIIT. 



night at the autumnal equinox. But the motion of the equinoctial points 

 having changed in some degree the course of the seasons with regard to the 

 stars, the signs of the ecliptic, by which the places of the sun and planets 

 are described, no longer coincide precisely with the constellations of the 

 zodiac from which they derive their names. 



The most ancient observations of which we are in possession, that are suffi- 

 ciently accurate to be employed in astronomical calculations, are those made 

 at Babylon in the years 719 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 Chaldeans, 

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

 discover their Saros or lunar period of 65854- <J^ys, 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 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 36.5 days each. The accurate corres- 

 pondence of the faces of their pyramids with the points of the compass is con- 

 sidered as a proof of the precision of their observations: but their greatest 

 merit was the discovery that Mercury and A'^enus 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. 5^5, 62,6.} 



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 

 C)nfjrmed by an incontestable series of historical monuments. The regula- 

 tion of the calendar, and the prediction of eclipses, were regarded in this 

 country as important objects, for which a mathematical tribunal was esta* 

 blished at a very early period. But the scrupulous attachment of the Chinese 



