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 bemgs 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 
