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CHAPTER X. 



THEORY OP COMETS. 



1. The Comets are planets moving in very eccentric conic sections. 



2. To determine the particular orbit of a given comet. 



(1.) THE visit of a comet presents to us a great mys 

 tery. It comes unexpectedly, remains but a short time, 

 often presenting a magnificent spectacle, and then dis 

 appears in a manner as wonderful as its appearance. It 

 is one of those great problems that God has set before 

 us. Many of the ancients regarded them * as simple 

 meteors, sent from the Supreme Being as signs of his 

 anger or prognostics of future events. Others, as the 

 illustrious Seneca, had better views on the subject &quot;I 

 do not follow the opinion of our philosophers ; I do not 

 consider the comets to be passing fires, but as one of the 

 eternal works of nature.&quot;! 



Newton set about the solution of this great problem 

 in his usual logical manner. The first point to be settled 

 was whether they were simple meteors of our atmosphere 

 or not. Their want of diurnal parallax is a convincing 

 proof that they are at least further off than the moon. 

 But how much further? We must have some idea of 

 their distance to determine to what class of forces their 



* Pingr, Comet ; Bossut, Hist, de Math. 

 f Seneca, Nat. Quaest. lib. vii. 



