The Romance of the Heavens 35 



and are extraordinarily gaunt and rugged. They are like foun- 

 tains of lava, rising in places to 26,000 and 27,000 feet. The 

 lunar Apennines have three thousand steep and weird peaks. 

 Our terrestrial mountains are continually worn down by frost 

 acting on moisture and by ice and water, but there are none of 

 these agencies operating on the moon. Its mountains are com- 

 paratively ''everlasting hills." 



The moon is interesting to us precisely because it is a dead 

 world. It seems to show how the earth, or any cooling metal 

 globe, will evolve in the remote future. We do not know if there 

 was ever life on the moon, but in any case it cannot have pro- 

 ceeded far in development. At the most we can imagine some 

 strange lowly forms of vegetation lingering here and there in 

 pools of heavy gas, expanding during the blaze of the sun's long 



day, and frozen rigid during the long night. 



I 



METEORS AND COMETS 



We may conclude our survey of the solar system with a word 

 about "shooting stars," or meteors, and comets. There are few 

 now who do not know that the streak of fire which suddenly lights 

 the sky overhead at night means that a piece of stone or iron has 

 entered our atmosphere from outer space, and has been burned 

 up by friction. It was travelling at, perhaps, twenty or 

 thirty miles a second. At seventy or eighty miles above our 

 heads it began to glow, as at that height the air is thick enough 

 to offer serious friction and raise it to a white heat. By the 

 time the meteor reached about twenty miles or so from the 

 earth's surface it was entirely dissipated, as a rule in fiery 

 vapour. 



Millions of Meteorites 



It is estimated that between ten and a hundred million 

 meteorites enter our atmosphere and are cremated, every day. 



