ASTRONOMY. 13 



which time developes so slowly in the system of the 

 primary planets. Abundance of materials have there- 

 fore been collected for a comparison between fact 

 and theory. 



Grand Conjunction. 



In 1748 the attention of astronomers was attracted 

 to the conjunction of five planets, in one sign of the 

 zodiac, a phenomenon that had not before occurred 

 since the creation of the universe. 



Number of Stars. 



Of the stars in the British catalogue, there are 

 many only visible through a telescope, nor does the 

 eye ever see more than a thousand at the same time 

 in the clearest heaven ; yet the number is probably 

 infinite. From the first to the sixth magnitude, in- 

 clusive, the total number of stars is 3,128. 



The Zodiac. 



The sun never deviates from the ecliptic or middle 

 of the zodiac ; the planets all do, more or less. Their 

 greatest deviations, which never exceed 20 degrees, 

 form the extreme breadth of the zodiac. The zodi- 

 acal light is supposed to be the visible substance of 

 the solar atmosphere. 



The Chaldean Cycle. 



Thales is supposed to have made some of his dis- 

 coveries by the help of the Chaldean cycle, called 

 Saros. This cycle consisted of 6585^- days, or 223 

 lunations, or 18 years, 15 days, and 8 hours; after 

 which the Chaldeans imagined, from a long series of 

 observations, that the eclipses of the sun and moon 

 returned again in the same order and quantity as 

 before. 



Theory of the Milky Way or Galaxy. 



Sir Wm. Herschel considers the milky way to be 

 an extensive branching congeries of stars, within 



