] 70 Physics of the Soil. 



Tn the case of the 6-inch cylinders of soil above, with 

 their tops only 11 inches out of water, the length of time 

 required for the surface of the soil to begin to appear 

 damp was 



2 days for the fine sand or 5th foot. 



6 days for the sand and clay or 4th foot. 



6 days for the clay loam or 1st foot. 

 18 days for the reddish clay or 3rd foot. 

 22 days for the reddish clay or 2nd foot. 



It is clear from the data presented that the rate of cap- 

 illary movement of soil moisture is greatly influenced by 

 the water content of the soil. 



198, Capillarity Is Stronger in Wet than in Dry Soib. It 

 follows from (196) and (197) that capillary action in a 

 given soil is stronger when the soil contains a. certain 

 amount of moisture than it is when that amount is much 

 reduced. When soils have their water content so much 

 reduced that they begin to look dry, and especially after 

 they become air-dry, they act as effective mulches and 

 water will neither rise through them so rapidly nor so high 

 the dryer they become, and if, under these conditions, a 

 light shower should fall it might have the effect of leaving 

 the surface soil with a greater increase of moisture than is 

 represented by the rain which fell. 



199. Rain May Cause a Capillary Bise of the Deeper Soil 

 Moisture. It was observed in 1889, when determining the 

 water content of soils at different depths in the field, just 

 before and immediately after rains, that frequently the 

 lower soil showed a smaller amount of moisture than it 

 had before the rain, while the surface layers had gained 

 in water more than that represented by the rainfall. It 

 was later shown that, by applying a known amount of 

 water to a section of a field, the lower soil became dryer 

 while the surface layers had gained more water than wag 

 added, as shown in the table. 



