364 THE CHEMISTKY OF CREATION. 



have been made as to the actual demand upon 

 the atmosphere for carbonic acid, of the whole 

 vegetation of the earth. If we suppose the actual 

 surface covered by vegetation to be one-fifth of 

 the entire area of our globe, that will give a 

 space of two millions of square miles, or of 

 43,124 millions of acres. Let us suppose that 

 each acre derives every year 2,000 Ibs. of carbon 

 from the air; then the whole annual necessi- 

 ties of the vegetable world in a year amounts 

 to about 300 billions of pounds of carbonic 

 acid. How is this enormous annual drain to be 

 supplied? Dr. Schleiden calculates that from 

 tobacco smoking alone we have a supply of car- 

 bonic acid in a year equivalent to 1,000 millions 

 of pounds. He bases this odd calculation on 

 the following grounds. North America alone 

 produces in a year enough tobacco, on its 

 being burnt, to yield the immense sum of 340 

 millions of pounds ! The other tobacco-grow- 

 ing districts supply the rest. Yet when we 

 contrast the insignificant cloud of smoke rising 

 from a single pipe more, perhaps, from those 

 used by Dr. Schleiden's continental country- 

 men than from our own together with that 

 rising from our furnaces and factories, how in- 

 significant does even this enormous sum appear, 

 compared with that which from combustion of 

 fuel alone escapes into the air ! When it is 



