136 The Great World's Farm 



blooded animals, and give off less carbon dioxide in pro- 

 portion. 



Whenever carbon is bu -ned by combining v/ith oxygen, 

 whether in food, coal, wocd, gas, oil, candle, or in decay- 

 ing vegetable-matter, there carbon dioxide is formed. It 

 is being constantly poured into the air, therefore, by men 

 and animals, by the chimneys of factories and houses, by 

 volcanoes, and by the soil. 



But it is not produced in anything hke equal quantities 

 in all parts of the world. Very little is returned to the air 

 above the ocean, and t'_at little chiefly by passing vessels; 

 and as there is more ocean than land in the southern 

 hemisphere, much less is produced there than in the north- 

 ern hemisphere, which is chiefly land. 



Then, again, the eastern hemisphere is much more 

 densely populated than the western, besides having, of 

 course, many more factories, furnaces, and engines of all 

 sorts, which are constantly burning carbon. It might 

 seem not improbable, therefore, that some parts of the 

 world, such as the islands of the Pacific, should be at 

 times in danger of not having carbon dioxide enough to 

 supply the wants of their vegetation, especially when we 

 consider that bananas, which need such large quantities, 

 form an important item in their crops. 



But the fact is not so; for the supply is equally dis- 

 tributed. More fires are kept burning, and more carbon 

 dioxide is produced in winter, when the trees are leafless 

 and do not want it, than in the summer, when they do. 

 And yet we are not choked by it, or even inconvenienced 

 by it, in the winter months, so it must be got rid of some- 

 how. For if there were two per cent in the air, we 

 should have severe headache, and ten per cent would 



