Nature- Study Agriculture 



W. T. SkiUinO 



FIG. 20. Free water and capillary water on a stone. Invisible water covers 

 the top of the stone. 



enough water to keep it moist, so the soil particles hold 

 moisture which clings to their surfaces and fills the small 

 spaces between them. This is called " capillary water," 

 and the force that holds the water is called " capillary 

 force." This force is named from the Latin word 

 " capilla," meaning a hair, because it acts best in very 

 narrow spaces. (Exp. 10.) Capillary force not only 

 makes a film of water cling to the particles, but it draws 

 the water up toward the drier surface of the ground. 

 It is capillarity that draws oil up in a wick, and that 

 causes water to rise in a very slender glass tube when we 

 dip one end of the tube in water (Fig. 21). Capillarity, 

 too, helps the sap to rise in the stems or trunks of plants. 



