268 INHABITED WORLDS. 



extreme in this respect to Jujtiter and Saturn ; it 

 is evidently a cold and burnt-out little world, 

 devoid of all its original fiery energy. It has no 

 water anywhere upon its surface ; no atmosphere 

 clothes it with a gaseous covering ; it exhibits one 

 terrible and deathlike scene of bare rocky volca- 

 noes and yawning craters, undiversified by the 

 foliage of trees or the green carpet of grasses, and 

 barren of any passing sign of animal and vege- 

 table life in any part of its desert ex})anses. 



Now, it is quite clear that, in either of these 

 two extremes of planetary existence — in the fiery 

 youtli of a world, or in its cold old age — the oc- 

 currence of life upon its surface, at least in any 

 form that we can at all realize, is absolutely incon- 

 ceivable. While a young earth is still in a molten 

 or semi-molten condition, like glass in a furnace, 

 plants or animals as we know them here could 

 not possibly exist upon its incandescent lava- 

 fields. On the other hand, when it has grown 

 old, chilly, waterless, and airless, when all its 

 oceans have been sucked up by its rocks, and all 

 its atmosphere slowly absorbed into its crust by 

 chemical action, the existence of any living thing 

 upon its bare and wrinkled face becomes of course 

 utterly impossible. Hence, even if we suppose 

 that every i)lanet is at some lime or other neces- 

 sarily and naturally fitted for supporting life, it 

 can do so only during its middle period, such a 



