Influence of Size 187 



too great to be supported. But the differ- 

 ence, as regards habitability, between a 

 palace and a hovel is far less than that 

 between a hovel and one of the air-holes in 

 a brick or loaf, or any other cavity too 

 small to act as a human habitation. The 

 difference as regards habitability is then an 

 infinite difference. 



To take a less trivial instance ; a planet 

 which is large enough to retain an atmo- 

 sphere by its gravitative attraction differs 

 utterly, in potentiality and importance, from 

 the numerous lumps of matter scattered 

 throughout space, which, though they may 

 be as large as a haystack or a mountain or 

 as the British Isles, or even Europe, are yet 

 too small to hold any trace of air to their 

 surface, and therefore cannot in any 

 intelligible sense of the word be regarded as 

 habitable. One of the lumps of matter in 

 space can become a habitable planet only 

 when it has attained a certain size, which 

 conceivably it might do by falling together 

 with others into a complex aggregate under 



