PRINCIPLES OF WEATHER FORECASTING, 



CHAPTER XXIV. 

 THE ATMOSPHERE. 



As the life processes of all plants and animals are de- 

 pendent upon the air, and are greatly influenced by changes 

 in ft, it is eminently proper that the atmosphere and its 

 changes should be considered in their relations to agricul- 

 ture. From the standpoint of food supply the clover crop, 

 for example, containing at maturity 70 per cent, of water, 

 has directly or indirectly obtained all but its ash in- 

 gredients from the atmosphere. The water is brought to 

 the soil as rain, the carbon comes from the carbon dioxide 

 and the nitrogen is obtained from the soil air by the free- 

 nitrogen-fixing bacteria. The relations stand 



Water from the atmosphere as rain 70.00 per cent. 



Nitro.-ron from the soil-air 70 per cent. 



Carboo and oxygen from the atmospi.cie as rain and carbon 



dioxide 26.57 per cent. 



Ash ingredients from the soil 2.73 per cent. 



Total 100. 00 per cent. 



Thus 97.27 per cent, cf the plant food is derived from 

 the constituents of the atmosphere, either directly or in- 

 directly. 



700. Relation of the Atmosphere to the Earth. The earth 

 consists of three concentric spheres, (1) at the center, the 

 solid, or earth-sphere; (2) surrounding this is the liquid or 



