60 PHYSICAL SCIENCE BK. n 



through the centre of objects by which it appears 

 to be parted. The interposition of walls and high 

 mountains renders it impassable by us, but is no 

 obstacle to itself. The air is there all the same, 1 

 but a portion is enclosed and we cannot follow it 

 through ; that's all. 



1 THUS the air passes through the middle of an 

 obstacle by which it is apparently divided. It not 

 merely surrounds and encircles all objects, but 

 permeates them likewise. It is shed abroad from 

 the bright ether on high down to the very earth. 

 It is nimbler and rarer and more exalted than the 

 earth, and no less so than the waters of earth ; 

 but, on the contrary, it is thicker and heavier than 

 the ether, and is naturally cold and dark, its light 

 and heat coming from without. It is not of the 

 same specific quality in every region, but borrows 



2 its qualities from its surroundings. The highest 

 part of it is extremely dry and hot, and so, very 

 rare also, from the proximity of the eternal fires, 

 the endless motions of the stars, and the constant 

 revolution of the heavens. But the lowest portion 

 next the earth is dense and dark, because it forms 

 a receptacle for the exhalations of the earth. The 

 intermediate portion, in dryness and rarity, runs 

 to neither extreme as compared with the highest 



3 and lowest strata, but is colder than either. The 

 reason is this : The higher parts are affected by 

 the heat of the heavenly bodies that are close by; 

 and again the lower parts are warmed in the first 



1 The general sense is clear, but the particular text is uncertain. 



