CHAPTER II. 



GREEK ASTRONOMY. 



" The astronomer discovers that geometry, a pure abstraction of the 

 human mind, is the measure of planetary motion." 



EMERSON. 



19. IN the earlier period of Greek history one of the 

 chief functions expected of astronomers was the proper 

 regulation of the calendar. The Greeks, like earlier 

 nations, began with a calendar based on the moon. In 

 the time of Hesiod a year consisting of 12 months of 30 

 days was in common use ; at a later date a year made up 

 of 6 full months of 30 days and 6 empty months of 29 days 

 was introduced. To Solon is attributed the merit of 

 having introduced at Athens, about 594 B.C., the practice 

 of adding to every alternate year a " full " month. Thus a 

 period of two years would contain 13 months of 30 days 

 and 12 of 29 days, or 738 days in all, distributed among 

 25 months, giving, for the average length of the year and 

 month, 369 days and about 29^ days respectively. This 

 arrangement was further improved by the introduction, 

 probably during the 5th century B.C., of the octaeteris, or 

 eight-year cycle, in three of the years of which an additional 

 " full " month was introduced, while the remaining years 

 consisted as before of 6 " full " and 6 " empty " months. 

 By this arrangement the average length of the year was 

 reduced to 365! days, that of the month remaining nearly 

 unchanged. As, however, the Greeks laid some stress on 

 beginning the month when the new moon was first visible, 

 it was necessary to make from time to time arbitrary 

 alterations in the calendar, and considerable confusion 



