TILE DRAINAGE. 69 



yet the perpendicular and diagonal porosity is constantly 

 increased, especially after they are tiled, by the rains soak- 

 ing down and through to the tiles, and by the roots growing 

 down vertically and diagonally, as well as horizontally, 

 though to less extent horizontally, after drainage than be- 

 fore. And so the most of our subsoils are not, like loose 

 sand or granulated sugar, equally porous in all directions, 

 but are most porous horizontally, and next most porous ver- 

 tically. 



Refer once more to Fig. 18, in which I have tried to illus- 

 trate this in a rough way. Suppose tile drains to be located 

 at r and D. Then the rain falling (in a dry time for exam- 

 ple) on the slightly uneven surface of the ground all the 

 way from A to B, soaks straight down, at first, at all points 

 on the surface, and not very much sidewise because it falls 

 on all points alike. If the ground is at first quite dry it 

 drinks in the rain rapidly and greedily, not only into the 

 proper air-spaces, but into the larger capillaries, which are 

 now empty for some distance down because the level of hy- 

 drostatic water is low from the general dryness If the rain 

 continues long enough, then all the pores, large and small, 

 air-spaces and capillaries, soon become filled full up to the 

 level of C and D. Then if the rain continues, as the water 

 can not go down any longer below and D it will be forced 

 sidewise, horizontally, and sometimes diagonally, by the 

 force of gravity, or hydrostatic pressure, and will enter the 

 tiles and flow off. And the' point I wish to emphasize is, 

 that, if the soil acts as it should (the drains being laid 

 straight down the slope), the water will enter the tiles as 

 fast as all the pores at all points of the surface can receive and 

 convey it. But if the drains are laid across the slope, and 

 the water is carried down the slope along the surface to a 

 line directly over the drain, then it can soak down to the 

 tiles only as fast as the pores in this single narrow strip of 

 soil can receive and convey it down. And so, instead of 

 having the whole area of the field as a filter, you have simply 



