UNDERDRAINING AND DEEP TILLAGE. 125 



The first and mos^ important benefit is that it warms the soil ; 

 and this it does in several wajs. It permits the stagnant water in 

 the soil to pass through it, and allows the v/arm rains of summer to 

 go down, carrjing warmth in their course. This warmth upon un- 

 drained soil is unavailable because it escapes into the air instead 

 of being retained in the soil. Water is so poor a conductor of heat 

 that it is nearly impossible to make heat pass downwards in it. 

 This can be easily proved by the simple experiment of boiling, or 

 trying to boil, a kettle of water by heat applied at the top. A few 

 inches might receive some warmth, but the effect of the heat would 

 not be felt much lower, or to any great degree. The same principle 

 operates to prevent the subsoil in saturated ground from receiving 

 and holding the heat falling on the surface. The heat will not pass 

 downward in the water filling the soil, but the warmer portions of 

 ■water remain on the top and give off their heat to the air. This is 

 of course the same, whether the heat at the surface comes from warm 

 rains in summer, or from the sun ; the subsoil in land containing 

 superfluous water will not be warmed by heat at the surface of the 

 ground. But when the surplus water is withdrawn by means of a 

 drain, the water at the surface, falling by its own weight, takes the 

 place occupied by the lower stratum before, and, although it may be 

 but a moment in passing through the soil, it gives up its heat to it. 

 Now the h.eat in the warm rains in summer can by this means, be 

 readily saved to the soil on which they fall, and the heat given by 

 the sun's rays may be retained as a gain instead of being wholly lost. 

 That such heat at the surface may be an injury, veiy few would be 

 willing to admit, at first sight, unless we confined such injury to 

 drought and baking of land. But we desire to make this statement 

 which Ave shall find to be correct, that heat given to the surface of 

 undrained land, in fact produces cold. This seeming paradox is 

 accounted for by the fact that evaporation produces, as a primary 

 result, cold ; and evaporation is hastened by heat. Thus in the 

 case of a vessel of water on a stove, just as much heat is taken from 

 the vessel as is required to change the water to vapor. It is also 

 seen in the method employed in the warm months, to cool water. 

 A wet towel is wrapped around the pitcher, and by the evaporation 

 of the moisture in the cloth, sufficient heat is taken from the pitcher 

 to cool the water several degrees. This principle that evaporation 



