AERATION OF THE SAP. 35 



tend to its purification and to its remaining 

 adapted to the respiration of animals. Nearly 

 the whole of the carbon accumulated by vege- 

 tables is so much taken from the atmosphere, 

 which is the primary source from which they 

 derive that element. At the season of the year 

 when vegetation is most active, the days are 

 longer than the nights ; so that the diurnal pro- 

 cess of purification goes on for a greater number 

 of hours than the nocturnal process by which the 

 air is vitiated. 



The oxygen given out by plants, and the car- 

 bonic acid resulting from animal respiration, 

 and from the various processes of combustion, 

 which are going on in every part of the world, 

 are quickly spread through the atmosj^here, not 

 only from the tendency of all gases to uniform 

 diffusion, but also from the action of the winds, 

 which are continually agitating the whole mass, 

 and promoting the thorough mingling of its dif- 

 ferent portions, so as to render it perfectly ho- 

 mogeneous in every region of the globe, and at 

 every elevation above the surface. 



Thus are the two great organized kingdoms of 

 the creation made to co-operate in the execution 

 of the same design : each ministering to the 

 other, and preserving that due balance in the 

 constitution of the atmosphere, which adapts it 

 to the welfare and activity of every order of 

 beings, and which would soon be destroyed, were 

 the operations of any one of them to be sus- 



