

ASTRONOMY. 3 



sun and moon were formed. As we have now no 

 light, but what comes either from the sun himself, or 

 by reflection from the moon ; and as there was light 

 and also day and night before the sun and moon 

 were formed, we must infer that the day here men- 

 tioned has been of a different character from our 

 day, and that this light had a different source from 

 an immediate communication with the sun. We may 

 therefore conclude that during the incipient formation 

 of our planet, it possessed a light peculiar to its own 

 constitution, which appears also to accompany other 

 heavenly bodies, such as comets, in a similar stage 

 of their formation. 



The Light and Revolution of Comets. 



When comets are advancing towards their perihe- 

 lium, and at different distances approach nearer the 

 earth, we observe that they are not only surrounded 

 by a luminous atmosphere, but have a long luminous 

 tail, both of which become greater as they approach 

 the sun, and decrease as they recede from him. In 

 the case of some, almost the whole mass is changed 

 into this luminous atmosphere and tail ; in others we 

 perceive a distinct red nucleus, which on approach- 

 ing the sun becomes a less expanded atmosphere and 

 tail. Bessel calculated the period of the revolution 

 of the comet of 181 1 to be 3,383 years ; Sir William 

 Herschel made the radius of its atmosphere 322,000 

 English miles, and the length of its tail more than 

 100 millions of miles. He also believed that it re- 

 volved on its axis, and that during each perihelium they 

 approached nearer and nearer to the sun, while their 

 orbits approached nearer and nearer to the circular 

 form. A remarkable comet is expected in 1835. 



A Comet's Tail. 

 It must be admitted that before a comet can have 



