53G ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



Permeability of the Soil to Water. 



In general, if the soil be saturated with water, the down- 

 ward flow will be faster in coarse and loose, and slower in 

 line and compact soils. But when rain falls on a dry soil, aft- 

 er it works down to a point where interstices are filled by 

 capillarity with water from below, the downward flow would 

 probably be faster in the finer soil. 



Water-holding Capacity of the Soil. 



As regards the "absolute water capacity" of the soil the 

 amount it will retain and hold for the use of plants it may 

 be said that, in general, falling water will be held more firm- 

 ly, and hydrostatic, or "bottom," water will, by capillarity, 

 be drawn up higher in the finer and more compact than in 

 the coarser and looser soils. Porosity of particles would 

 tend to equalize distribution and make upper layers more 

 moist. If we have a fine, compact soil over a loose sub- 

 soil, water falling on the top will not be drawn down- 

 ward so forcibly as if the subsoil were finer and had 

 more capillary power; that is to say, "a soil thus situ- 

 ated is not so well drained as if the subsoil were as fine 

 as itself. The reason why such a soil is dryer than one 

 on a fine subsoil is, that the water held bv it soon dries 

 out in fair weather, and the subsoil cannot raise water fast 

 enough to supply the loss." 



Evaporation of Water from the Soil. 



Aside from temperature and exposure, the main factors 

 of surface evaporation from the soil are, (1) capillarity, and 

 (2) extent of surface exposed to evaporation. The most im- 

 portant factor is capillarity that is, the rapidity with which 

 the soil permits water to rise in it to supply a deficiency at 

 any point, and hence to keep up a supply to be evaporated 

 from the surface. In general, the finer the soil the greater 

 the capillarity down to a certain smallness of grain. It is 

 probable that the pores may be so small as to retard the mo- 

 tion of the water. As regards texture, close packing would, 

 like greater fineness, tend to aid capillarity, until the pores 

 become so small as to retard the flow. 



As regards the effect of evaporating surface, it is to be 



