92 THE WORLD. 



like ourselves, but they endeavored to perpetuate the memory of 

 great events by recording the positions of the heavenly bodies at 

 the time ; and in this, at least, they exhibited wisdom. We find 

 continual evidences of this, particularly in the poets of those earjy 

 ages. The Egyptians, to whom the overflowing of the Nile was 

 an annual, and in some respects, a dreaded occurrence, were ac- 

 customed to watch for the heliacal rising of the dog-star, which 

 warned them to gather their wandering flocks and herds, and 

 prepare for the coming flood. Hence, that star was called Thoth, 

 the watch-dog, the Guardian of Egypt. 



The stars rise or set heliacally, when they rise just before, or 

 set just after the sun. They are said to rise or set cosmically, 

 when they rise or set just at sunrise, and to rise or set acronycally 

 when they rise or set just at sunset. It will appear that the heliacal 

 rising, or setting, will precede or follow the cosmical rising, or the 

 acronycal setting, by about 12 or 15 days, for a star cannot be seen 

 unless the sun is 12 or 15 below the horizon, and the sun 

 moves over about a degree in a day. Pliny says that Thales, the 

 Miletian. astronomer, determined the cosmical setting of the 

 Pleiades to be 25 days after the autumnal equinox. At the present 

 time, the same event occurs about 60 days after the equinox, 

 making a difference of 35 days, which, allowing 59' to a day, 

 makes 34 25' change in longitude, due to the precession of the 

 equinoxes. This, divided by the annual precession, 50.2", gives 

 about 2465 years since the time of Thales, or 620 years before 

 Christ. We find, also, in Hesiod, the number of days after the 

 winter solstice, when Arcturus rose acronycally, 



" When from the solstice sixty wintry days 

 Their turns have finish'd, mark, with glitt'ring rays, 

 From Ocean's sacred flood, Arcturus rise, 

 Then first to gild the dusky evening skies." 



But as we know the latitude of Bccotia, where Hesiod lived; we 

 can determine the acronycal rising of Arcturus, and by means of 

 the difference between the time how, and the time mentioned by 

 him, which is due to precession, can determine the age in which 

 he flourished. From actual observation, it is ascertained that now 

 this star rises at sunset about 100 days after the winter sclstict. 



