X THE STARRY HEAVENS 401 



appear to be still in a state of vapour. The 

 Moon has no air or water. 



Mars is in a condition which most nearly 

 resembles ours. All, however, that can be 

 said is that, so far as we can see, the exis- 

 tence of living beings on Mars is not impos- 

 sible. 



COMETS 



The Sun, Moon, and Stars, glorious and 

 wonderful as they are, though regarded with 

 great interest, and in some cases worshipped 

 as deities, excited the imagination of our 

 ancestors less than might have been expected, 

 and even now attract comparatively little 

 attention, from the fact that they are always 

 with us. Comets, on the other hand, both as 

 rare and occasional visitors, from their large 

 size and rapid changes, were regarded in 

 ancient times with dread and with amaze- 

 ment. 



Some Comets revolve round the Sun in 

 ellipses, but many, if not- the majority, are 

 visitors indeed, for having once passed round 

 2d 



