A. Because the fewer the inhabitants, _the less carbonic acid will be exhaled_; and thus country people will inhale _pure oxygen_, instead of air _impregnated with the narcotic poison_, called carbonic acid gas. Q. _Why do TREES and FLOWERS help to make country AIR WHOLESOME?_ A. Because trees and flowers _absorb the carbonic acid_ generated by the lungs of animals, putrid substances, and other noxious exhalations. Q. _Why is the AIR of CITIES LESS wholesome than COUNTRY air?_ A. 1st--Because there are _more inhabitants_ to vitiate the air: 2ndly--The _sewers_, _drains_, _bins_, and _filth of a city_, very greatly vitiate the air: 3rdly--The streets and alleys prevent a free circulation: and 4thly--Besides all this, there are fewer trees to absorb the excess of carbonic acid gas, and _restore the equilibrium_. Q. _Why are PERSONS who live in CLOSE ROOMS and crowded CITIES, generally SICKLY?_ A. Because the air they breathe is not pure, but is both _defective in oxygen_, and impregnated with _carbonic acid gas_. Q. _Where does the CARBONIC ACID of close ROOMS and CITIES COME from?_ 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 vegetables_, 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 through their eyes and ears_, producing an intense pain. Q. _Why is it often PAINFUL, and difficult to BREATHE, on a MOUNTAIN top?_ A. Because the pressure of air on the mountain top is _not so great as on the plain_; and the air inside our bodies (seeking to become of the same rarity) _bursts through the pores of the body_, and produces great pain. Q. _Why do we feel OPPRESSED just PREVIOUS to a STORM?_ A. Because the air is _greatly rarefied by heat and vapour_; and the air inside us (seeking to become of the same rarity) produces an oppressive and suffocating feeling. Q. _Why do DIVERS suffer great pain in their eyes and ears under water?_ A. Because the air at the bottom of the sea _is more dense_ than the air _on the surface_; and while the air inside the diver's body is settling into the same density, he feels oppressed with pain, especially in the ears. Q. _Why is this PAIN felt especially about the EARS of a DIVER?_