24 ENGINEERING FOR LAND DRAINAGE. 



replenishing the supply of capillary water. When this 

 is accomplished, the surplus should be drawn off by 

 the process of drainage in order that air and gases may 

 take its place. These in connection with heat and 

 moisture aid in the decomposition of organic and min- 

 eral components of the soil which constitute its fertility. 

 Excess of water retards, and in many cases altogether 

 prevents this process. 



It is the province of drainage to remove the surplus 

 water and retain the capillary water, since it is in the 

 latter form only that water is appropriated by useful 

 plants. By the removal of hydrostatic water the 

 chemical forces of the soil are permitted to work freely 

 in their laboratory, and thus prepare the elements of 

 the soil for plant use. 



Experimental hivestigations . 



Many of the changes which take place in soils by 

 reason of the presence of water in varying quantities 

 are now being made the subject of careful examination 

 at some of our experiment stations. This is particu- 

 larly true of mechanical analyses of soils, and observa- 

 tions upon the movement of water in soils possessing 

 different physical characteristics. It is interesting to 

 note that the operations and effects of drains upon the 

 soil as heretofore recorded by close observers, agree 

 very closely with the results of experiments made in 

 recent years for the purpose of ascertaining the facts with 

 scientific precision. To the soil physicist, the engineer, 

 and the observing agriculturist these investigations 

 are in every way interesting and useful. While experi- 



