TILE DKAINAGE. 11 



that the hydrostatic water is at or near the surface all 

 through the soil. When water oozes frc m the ground, as on 

 slopes, you may know that gravity (hydrostatic pressure) is 

 forcing it out here from a higher level. 



In a dry time the hydrostatic water sinks several inches or 

 even feet below the surface in land not tiled or drained by 

 nature. This is because the capillaries have previously 

 carried it to the surface, and the hot dry atmosphere has 

 evaporated and absorbed it, as will be seen presently. You 

 can find just how near to the surface the hydrostatic water 

 stands at any time, simply by digging a hole in the ground. 

 The hole will soon fill up to the top level of complete satura- 

 tion ; i.e., of hydrostatic water in the ground. In a wet 

 time this hole may be a mere post-hole, and may stand full 

 to the very surface. In a very dry time the "hole" will 

 need to be a deep well, perhaps. But the surface-water in 

 each will show the top level of the hydrostatic water that is 

 within reach of hydrostatic pressure ; for hydrostatic press- 

 ure and capillarity are constantly opposing forces. One 

 pushes the water down ; the other lifts it up. One is simply 

 the force of gravity acting on the water. The other is a 

 kind of adhesive attraction between the water and the 

 sides of the pores in the soil. Where these pores are very 

 large, as in gravel or coarse sand, there gravity acts nearly 

 unobstructed, and hence rapidly and over long distances ; 

 and so the sand or gravel " veins " or seams in clay subsoils 

 are the " water-bearing strata ?? for wells and springs, and 

 bring water into them rapidly, and often from long distances. 

 If a tight tube or curb is inserted in the well or spring, the 

 water will quickly rise to the level of its source, even if that 

 is many rods away, and the filtration in such coarse sand is 

 imperfect. In a hamlet in Switzerland, all who drank from 

 a certain spring had typhoid fever. It was traced to the ex- 

 cretions of a typhoid patient, which were thrown out witli 

 slops upon the ground, over half a mile distant, and over 

 quite a hill. Proof positive was given by pouring a large 



