82 FARM DEVELOPMENT 



much water, plants can better endure either periods of 

 drouth or an excessive rainfall. Vegetable manures 

 added to soils, green crops plowed under, or the roots of 

 plants in the soil, soon decay, and while decaying these 

 substances aid the soil in retaining capillary moisture. 



Capillarity illustrated. The word capillarity has such 

 an important use and meaning that an explanation is 

 necessary. It is derived from the 

 Latin word capillus, meaning a hair. 



In Figure 30 are shown several 

 very small glass tubes with their ends 

 dipped in water. It will be observed 

 Figure so. showing how that the water rises inside the tubes. 



water rises in small capil- . . 



lary tubes, it rises higher i ne water and the inside surface of 



in the smaller tubes than 



in the larger ones. the glass have an affinity for each 



other sufficient to draw the fluid up into the tubes. The 



fact that this action of water in very minute hairlike 



tubes was the first clearly observed case 



in which water attached to and crept 



over surfaces and through small open- 



ings is probably the reason that the 



name capillary action was given to this 



movement of water in the soil. It will 



be observed in the illustration that the 



water rises higher in the smaller tubes Figure si. when two 



. t , 1 1 rri r plates of glass, placed 



than in the larger ones. The force ex- so as to touch at one 



t . . edge and % inch apart 



erted is the attraction of the water and a ,t the other edge have 



their ends placed in 



the inner surface of the glass for each 



other. In the small tubes the surface S^iSSSS *! 



of glass is larger in proportion to the **?**&$, * 



load of water than in the tubes where gether ' 



the column of water has a greater diameter. The action 



of this force is further illustrated in Figure 31, showing 



that it is not the form of the tube, but the attraction of 



the surfaces of the glass, which carries the water up- 



ward. The attraction of the water for the surfaces is 



