THE MOISTIRK IN THK SOIL .V.) 



illustrated liy filling straight (or artfand) lamp chiiuiK'ys with 

 lumpuctfil dry soil and standing thfui in a dish of wati-r. 



GS'i. Film moisture <'an ho inustratt-d by dippinir ii niarhlu 

 into water and observing tho skin or film of moisfnro adhering to 

 nil sides. The most satisfactory conditions of soil moisture exist 

 when ••aeh soil grain is covered by a film of wati-r. The char- 

 acter of film moisture is changed by the thickness of the film. 

 The thicker the film, the less the tension to the body, until 

 it becomes so thick as to separate from that boily and become a 

 drop of water ; and it is then subject to tho law of gravitation, 

 and can travel but in one direction — downward. While in a state 

 of film moisture, it is amenable to the law of ••apillary attraction, 

 and can move in any direction, which means that it goes towards 

 the thinnest films. The readiness with which water films travel 

 can be sei'U by dipping a piece of cube sugar into coffee and 

 obser>'ing how quickly the liquid pervades the lump of sugar. 

 That soil moisture may move with the same facility as the 

 coffee does in the sugar, it is necessary to have the soil grains 

 in proper touch one witli another; — not so far apart but thai 

 the water films can rea«di one to the other, not so close as t<> 

 impede the progrehs of the films. The two ettremes in soil can 

 t'e gt<en in loose giavel and h.ird day. 



70rt. By rainf.all is meant precipitation, — the fall of water in 

 my form, as in niin, snow and hail. 



T2a. That different soils vary in their capacity t<> hold 

 iiioiHturv may t>e illustrated by the following experiment : Pro- 

 vide seveml flower- pots of the same size and shape. The va- 

 rmus Roils should be thoroughly dried in an oven. At least 

 four kinds of soil should bo tested: gravel, sand, clay, and gar- 

 den loam. Place an equal weight of each soil in the pots. 

 'm| one of the pots from a common spring-scales (Fig. 11). 

 the numlH>r of pounds and ounces registered. Now 

 -nwiy pour water U|H)n the soil until it is thoroughly saturated. 

 < over with a piin-e ot oiled cloth or oiled paper, and allow it 

 ••> drain until no more water will How from it. Th«' water 

 Ahicb dr«ins from tho |K)t Is the free water. The tlifference in 

 ^v eight of the |>ot of noil before aoaking, and after tho drainage, 

 shows the amount of water held by capillarity. 



