116 COMETS. 



On gazing nations, from his fiery train 

 Of length enormous ; takes his ample round 

 Through depths of ether ; coasts unnumbered WOflds 

 Of more than solar glory ; doubles wide -^ 



Heaven's mighty cape, and then revisits earth, 

 From the long travel of a thousand years. Young. 

 Besides the primary and secondary planets, there are other ] 

 bodies which revolve round the sun, and consequently make • 

 apart of the solar system. These are called comets, and i 

 appear occasionally in every part of the heavens. They are 

 solid, opaque bodies, generally distinguished by a lucid train i 

 or tail, issuing from that side which is turned away from the I 

 sun. Most of them move in very elliptical orbits ; at one J 

 time coming very near the sun, even nearer than Mercury, ■] 

 and again receding to a distance far beyond the orbit of ^i 

 Uranus. The train is so transparent, that the fixed stars may ^ 

 be seen through it, and sometimes it extends to an immense J 

 distance in the heavens. The farther it reaches, the broader 1 

 it seems to become, and at times it is divided into rays.  



Viewed through a telescope, comets appear full of spots 

 and inequalities, and a vapour frequently renders it impos- , 

 sible to observe their figure. In a clear sky, however, the | 

 solid body of a comet oTten reflects a splendid light. That i 

 part of astronomy relating to comets is still imperfect, for the ^ 

 opinion once prevailed, that they were only meteors gene- i 

 rated in the air, like those we see in a clear night, vanishing * 

 in a few moments, and no care therefore was taken to ob- "i 

 serve or record their phenomena with accuracy. .| 



The number of comets belonging to the solar system is | 

 unknown. More than five hundred have appeared since the ^ 

 commencement of the christian era. The orbits of ninety- 

 eight comets, up to the year 1808, have been calculated j 

 but of all the comets the periods of only three are known 

 with any degree of certainty, being found to return at inter- 

 vals of seventy-five, one hundred twenty-nine, and five hun- 

 dred and seventy-five years ; and of these that which appear- 

 ed in 1680 is the most remarkable. This comet, which will 

 not appear again till the year 2225, at its greatest distance, 

 is about eleven thousand two hundred millions of miles from 

 the sun, while its least distance from the centre of the sun is 

 about four hundred ninety thousand miles. In that part of 

 its orbit nearest the sun, it flies, according to Newton, with 



