22 TILE DRAINAGE. 



der. But surplus water in the soil makes mud, the opposite 

 and enemy of dust. Further, a clayey soil long kept too 

 wet gets "puddled," especially if tramped by live stock or 

 worked with implements when too wet. This means the 

 filling and destruction of the air-spaces, restored only by 

 freezing in ridges, or by tiling and tillage. A puddled clay 

 soil dries into a hard, impervious, brick-like mass. Tile 

 drainage, proper tillage, rotation and care, and keeping live 

 stock off, will prevent this and make a clayey soil more 

 nearly like the fertile sandy and gravelly loams, naturally 

 underdrained and adapted to tillage and rotation of crops. 



Ninlh. This brings us naturally to the next proposition ; 

 viz., that til$ drainage of soils that need it greatly diminishes 

 the effect of frost in heaving out wheat, clover, etc , in winter 

 and spring. The action of frost in heaving out roots and 

 plants is powerful and very peculiar, and closely connected 

 with capillary c action. How is " hoar-frost " or " stool-ice " 

 formed V Capillary action brings moisture to the surface of 

 the ground, but can take it no further, for that is the top of 

 the capillary tubes or pores. It will not run off from the 

 surface, for capillarity is the adhesive attraction between 

 the water and the solid matter (earth) that forms- the sides of 

 the capillary pores or spaces, and hence the water can not 

 rise by this force higher than the top of the capillaries that 

 exert the force ; that is, it can not rise above the surface of 

 the ground. Further, the same force that lifts it to the sur- 

 face holds it there unless some other force takes it away. 

 Two other forces can remove it frost and warm air ; and 

 the capillaries will, so to speak, pump it to the surface as 

 fast as either of these can take it. Frost takes it up as fol- 

 lows : It first freezes a thin layer of this capillary water at 

 the surface of the ground, and keeps on freezing thin layers, 

 each under the bottom of the preceding, each lifting up all 

 previous ones by its own thickness ; and so, by morning of a 

 clear cold night, the surface of a damp field will be honey- 

 combed an inch or two deep with this stool-ice or hoar frost. 



