188 PRACTICAL IRRIGATION. 



there must be means for collecting the water; and second, means for 

 retaining it until it is needed. When we speak of soils and moun- 

 tains as reservoirs the word is not used in the technical sense, for 

 I believe that the great volume of water that continues to flow from 

 our mountains are held in the interstices of the soil and rocks. 



My own investigation shows that our different soils hold from 

 17 to 26 per cent of water, although some authorities make a much 

 larger percentage. 



Different kinds of soils vary in regard to their porosity, and 

 the same soils vary to a very great degree in regard to their ab- 

 sorptive power of water, depending upon the amount of moisture 

 already contained in them. For example, on the red mesa soil at 

 South Pasadena, v/here the soil was practically dry, containing a little 

 over one per cent, of water when the water was turned on, it only 

 absorbed one-twentieth of the amount of water in a given time that 

 was absorbed by soil of the same kind which contained at the be- 

 ginning of the experiment about eight per cent, of moisture. This 

 may be an extreme case but it is remarkable how much water will 

 run off from the soil when it is dry. We see the same effect if we 

 dip a dry feather in water, when we pull it out it comes out dry. 

 But if we moisten it, and then dip it in water, it comes out saturated. 

 It seems necessary then in order to have our land absorb the maxi- 

 mum amount of water in the minlnmum amount of time, that the 

 soil should retain a goodly percentage of moisture. Or, In other words, 

 if we wish to fill our mountains and soils with water and preserve 

 the greatest amount of rainfall, they should be kept moist. 



Having shown that it is necessary to have some moisture in the 

 soil in order to have it absorb the rainfall readily, and thus make 

 our mountains an arable reservoir, let us look at the other side of 

 the case — that of retaining the moisture; and I regret to say that 

 the experiments are not so complete and numerous as they should 

 be, as they have only been fairly begun. 



In the first place let me call attention to the fact that capillary 

 action in soil is in every direction from a given point. Water spreads 

 out sidewise as well as upwards and downwards by this action. Soil 

 that was thoroughly irrigated was taken and the amount of water 

 determined at 26.12 per cent. Some of this soil was put in beakers, 

 filling them about half full and placed in the laboratory. On the fol- 

 lowing day 66 per cent, of the moisture had dried out. Tin cans 

 without either bottom-? or tops were pressed down into the soil and 



