20 LIFE ON THE FARM. 



dry. It is the air which takes the water away. The 

 air has a power within itself of taking water away 

 from things. This is called evaporation, because 

 the water thus taken by the air can no longer be 

 seen, but takes the form of an invisible vapor. The 

 power of evaporation must, in one sense, be 

 stronger than either surface tension or gravity. 

 Surface tension pulls water away from gravity, yet 

 the vaporizing power of air takes it away from 

 both. These three forces acting together on water 

 in the soil are the main ones with which the 

 farmer has to deal. Surface tension and evapora- 

 tion are not studied or understood so much as they 

 should be in order to get the best results from the 

 cultivation of the soil. 



WHERE THE WATER GOES. 



Water falling upon the earth either flows away 

 or sinks down to be kept in store for plants. If 

 the soil be already filled with water, most of it runs 

 away; but when the earth is dry, and the rain does 

 not fall .too fast, nearly all of it is absorbed. Dur- 

 ing the winter season, when little evaporation takes 

 place, on account of the low temperature of the 

 air and the frozen condition of the soil, a great 

 amount of water accumulates. Some of it is kept 

 within a few feet of the surface and some sinks 

 very deep, according to the nature of the soil below 

 the top layer, that is, the subsoil. If the subsoil 

 is of a loose, open nature, like sand or gravel, the 



