Campbell's 1902 Soil Culture Manual. 



41 



while the balance of the free water finds its way on down until it is all dis- 

 tributed. The next rain will result the same as is shown in section 2, only 

 we have 6, 8, or 12 inches more moist soil for it to pass through before 

 reaching the dry soil. 



A little illustration here may make this more clear. In setting out our 

 cabbage or tomato plants in the spring of the year when the surface is dry 

 and fine we usually water them. Now, in our first application of water to 

 this dry surface we notice the water does not seem to percolate, but for a 

 little time remains dormant on the surface. After a little it finds its way 

 down through the dry particles by force of gravity, leaving each particle 

 it passes covered with a thin film of water. Then we apply a second 

 application of water while the surface is still moist and we notice 

 the water immediately disappears. The reason of non-percolation of the 

 first application is because of the resistance of the dry particles to moisture, 

 or repulsion for water. The quick movement of the second application of 

 water into the ground is the result of the attraction of water for water. 



This is a point of much importance, and buggests a little simple 

 experiment that will illustrate this more clearly. Take a piece of glass, or 

 a smooth earthen plate and oil it slightly, then put drops of water, a half 

 dozen or more on the glass, take a narrow piece of ordinary newspaper, 

 about one-half inch wide, let it extend from the thumb and finger about 

 two inches, slowly move it down so the end of the paper will come in con- 

 tact with a single drop of water. If you notice closely you will see a 

 remarkable resistance of the paper against the water. Very soon the little 

 pores begin to absorb the water, and the end of the paper becomes moist. 

 Now slowly raise the paper and notice how persistently the paper hangs to 

 the water. When it lets go there is a quick upward movement, thus 

 showing the power of attraction of water for water. Now steadily move 

 the fingers down slowly, watching the paper and you will notice when it 

 gets close to the water there is a sudden movement down, even while there 

 is a little space between the moisture on the paper and the water on the 

 glass. The power of attraction is made very perceptible by the quick 

 oonnection of the two moist particles. Now draw the paper across the 

 glass from one drop to the other, you will notice the water all hangs 

 together. You have a string or train of water two or three inches long, 

 trailing on behind your paper. 



This illustrates how easy it is to get moisture into the soil by keep- 

 ing the surface constantly loose and open, so that as the rain falls it soon 

 works its way through the larger pores until it reaches the moist particles 

 in the firm soil when it immediately percolates on down below. Here 

 again nature has done a great deal for the semi-arid belt. The peculiar 

 formation and size of the usual particle of soil is very favorable for perco- 

 lation; also for its return upward by capillary attraction to feed the plant 

 during our long dry seasons. The movement of this moisture upwards can 



