254 AIR. 



Q. Where does the CARBONIC ACID of close 

 BOOMS and CITIES COME /row ? 



A . From the lungs of the inhabitants, 

 the sewers, drains, and so on : besides, 

 trees and gardens are not numerous 

 enough to absorb the noxious gas as fast 

 as it is generated. 



Q. What BECOMES of the CARBONIC ACID of 

 crowded cities ? 



A. Some of it is absorbed by vegeta- 

 bles, and the rest is blown away by the 

 wind, and diffused through the whole 

 volume of the air. 



Q. Does not this constant diffusion of carbonic 

 acid affect the PURITY of the WHOLE AIR ? 



A. No ; because after it is thus 

 diffused, it is carried to various lands, 

 and absorbed in its passage by the 

 vegetable world. 



Q. Why do persons who ascend in balloons 

 .feel intense pain in their eyes and ears ? 



A. Because the air of the upper 

 regions is more rarefied than the air on 

 the earth ; and the air inside their bodies 

 (seeking to become of the same rarity) 

 bursts tfirough their eyes and ears, pro- 

 ducing an intense pain. 



