TILE DBAINAGE. 9 



that they need is held UP in the soil by what is called u capil- 

 lary attraction." Capillary attraction is the force of adhesion 

 betwe3n liquids and solids which makes water rise in small 

 or "hairlike" tubes; for "capillary 1 ' comes from a Latin 

 word which means hairlike. If several small glass tubes, 

 open at both top and bottom, and of different sizes (diame- 

 ters), have their lower ends standing in a dish of water, then 

 the water will rise in them above the surface of the water in 

 which they stand ; and the smaller the tubes are, the higher 

 the water will rise in them. Fig. 1 illustrates this. Let the 

 line AB represent the surface of the water, and 0, D, E, and 

 F, represent small glass tubes. The water will rise in them 

 to different heights, proportioned inversely to the diameters, 

 as shown in the figures. The same thing may be shown be- 

 tween plane surfaces close together. Set two panes of glass 

 into a pan of water vertically, with two vertical edges joined 

 and their sides diverging like a thin book set on end and 

 opened just a little. The water will rise between them and 

 be highest close to where the edges meet, as shown in Fig. 2. 



The point is, that water rises in small tubes or between 

 close surfaces, and remains above the level of its source. The 

 tubes need not be round or smooth or straight. They need 

 not be tubes at all, but simply small connected open spaces 

 between some sort of material surfaces. For example, the 

 wick of a lamp is a small bundle of crooked capillary spaces 

 or pores, and the wick lifts the oil in the lamp to the top of 

 the wick. The flame does not "draw" it. It simply con- 

 sumes it as the capillary attraction lifts it. A fine sponge, 

 with its lower end in water, lifts the water all through its 

 own pores. You pour water into the "saucer" of your 

 flower-pot, and capillary attraction lifts the water (entering 

 at the hole in the pot) all through its soil. In the same way 

 the water in the soil of a field is drawn to or near the sur- 

 face to supply vegetation in a dry time. It cnmes from the 

 water stored deeper down in a wet time. 



But the soil, like a sponge, has some spaces or pores too 



