168 THE CULTURE OF FARM CROPS. 



Water being a fluid seeks its level under all circumstances, 

 being forced to this level by its gravity or weight, and the 

 extreme mobility of its particles among each other. It is 

 clearly evident from common experience that water cannot 

 be heaped up as sand or earth may be ; nor can hollows ex- 

 ist in the surface of a body of it. If a barrel of it is set 

 upon high ground and the contents are let out they will 

 flow readily to any lower level; but the water cannot be 

 made to flow up again of its own motion or gravity or 

 weight. 



Now, when water falls in the form of rain upon high 

 ground which is underlaid by clay or hardpan, it sinks 

 down to this impervious stratum, and not being able to pass 

 through it, it flows along its surface down to lower levels, 

 until, gathering there in excessive quantities, or being arrest- 

 ed in its flow by some obstacle, it makes its escape to the 

 surface by some easy way ; through a bed of sand or gravel 

 in the form of springs ; or it spreads through this open and 

 permeable soil and forms swamps or fills the soil with stag- 

 nant water at certain depths, less or greater as the case may 

 be. When one digs down through the surface to this under 

 current of flowing water and taps it, the water rises and 

 makes a well, in which it maintains a height equal to the 

 level of its source or nearly so. Thus a w r ell is an artificial 

 spring under these circumstances, but when the water flows 

 into the well from the surrounding soil and does not rise 

 from the bottom it is not a spring well but simply a cistern 

 which is supplied from above by ordinary drainage. 



Remembering this fact, it is easily seen that when low 

 land is saturated with w r ater which comes from a higher 

 level it may be effectually drained by cutting a ditch to in- 

 tercept it at the foot of the slope ; and by carrying off this 

 water to a convenient outlet the whole of the lower land 

 may be freed from it in a very easy and economical manner. 



Ditches, required for drains should be 3 feet deep; but 

 under certain circumstances this depth may be less or more. 

 It has been already explained that soil has the property of 

 capillary attraction by which water is raised above its level 



