On the Solar and Lunar Period of 600 Tears. 33 



becaufe the great year is always completed at the end of 

 that period. 



No other ancient writer, however, makes any mention of 

 this great year ; but Pliny in his Natural Hiftory relates, 

 that Hipparchus had fixed the courfe of the fun and moon 

 at fix hundred years ; which feems to refer to a period of 

 that duration : and it is to be conjectured, that it was efta- 

 blifhed by the ancients in order to* compare the courfe of the 

 moon with that of the fun, and to foretel for a confiderable 

 time beforehand the phafes of the moon. 



This, indeed, was one of the principal objects of the 

 ancient aftronomy. Meto invented the period of nineteen 

 years, becaufe he believed that nineteen tropical folar years 

 made exactly 235 lunar months. Calippus quadrupled, this 

 period, and made a new one of 76 years. Hipparchus qua- 

 drupled thefe 76 years, and by thefe means obtained a more 

 accurate period of 304 years. 



Now it may be readily fuppofed, that Hipparchus, in the 

 hopes of deviating ftill lefs from the truth, at length doubled 

 his period, and brought it to 608 years •, for, otherwife, why 

 fhould he have fixed his period even at 6co years ? 



According to every conjecture, the great year is nothing 

 elfe than the laft doubled period of Hipparchus ; for, though 

 Pliny and his cotemporary Jofephus fpeak in round num- 

 bers of 600 years, or fix centuries, yet we know that ma- 

 thematical accuracy is not always obferved in the language 

 of common life and of hiftorians. 



Mr. Bailly explains the period of fix hu dred years in a 

 manner totally different. That aftronomer finds, like all 

 thofe converfant with the fubject, that 6od folar years form 

 no whole number of lunar months without a fraction : but 

 as that would be the cafe if the year were aftumed a little 

 longer, as it really is, he thence concludes that the year in 

 ancient times was actually fo long as the precifion of the 

 period of 600 years requires ; and befides, that thofe ages 

 Vol. I. D produced 



