136 THE GREEK ASTRONOMY. 



histories ; and their astronomy has never advanced beyond a very rude 

 and imperfect condition. 



We can only conjecture the mode in which the Chaldeans discovered 

 their Period of 18 years; and we may make very different supposi- 

 tions with regard to the degree of science by which they were led to 

 it. We may suppose, with Delambre, 54 that they carefully recorded 

 the eclipses which happened, and then, by the inspection of their regis- 

 ters, discovered that those of the moon recurred after a certain period. 

 Or we may suppose, with other authors, that they sedulously deter- 

 mined the motions of the moon, and having obtained these with con- 

 siderable accuracy, sought and found a period which should include 

 cycles of these motions. This latter mode of proceeding would imply 

 a considerable degree of knowledge. 



It appears probable rather that such a period was discovered by no- 

 ticing the recurrence of eclipses, than by studying the moon's motions. 

 After 6585i days, or 223 lunations, the same eclipses nearly will recur. 

 It is not contested that the Chaldeans were acquainted with this period, 

 which they called Saros ; or that they calculated eclipses by means 

 of it. 



Sect, 12. — Sequel to the Early Stages of Astronomy. 



Every stage of science has its train of practical applications and 

 systematic inferences, arising both from the demands of convenience 

 and curiosity, and from the pleasure which, as we have already said, 

 ingenuous and active-minded men feel in exercising the process of 

 deduction. The earliest condition of astronomy, in which it can be 

 looked upon as a science, exhibits several examples of such applica- 

 tions and inferences, of which we may mention a few. 



Prediction of Eclipses. — The Cycles which served to keep in order 

 the Calendar of the early nations of antiquity, in some instances en- 

 abled them also, as has just been stated, to predict Eclipses ; and this 

 application of knowledge necessarily excited great notice. Cleomedes, 

 in the time of Augustus, says, " We never see an eclipse happen which 

 has not been predicted by those who made use of the Tables." (vtto 



TU)V KaVOVLK&V.) 



Terrestrial Zones. — The globular form of the earth being assented 

 to, the doctrine of the sphere was applied to the earth as well as the 

 heavens; and the earth's surface was divided by various imaginary 



m A. A. p. 212. 



