103 



inch of water, evaporated under the ordinary atmospheric pressure 

 of 15 lbs. to the square inch, contains sufficient latent heat to raise 

 the temperature of 990 cubic inches of water one degree. A wet 

 soil, then, that has no way of freeing itself of an excess of water, 

 but by evaporation, will be cold for the reasons given, and the crop 

 will be both later and inferior to what it would be, provided the 

 soil was freed from this excess of moisture by drainage. Hence, 

 also, the liability to injury from frosts, both late and early, over 

 such undrained regions. 



Soils impregnated with stagnant waters are bad conductors of 

 heat from the sun downwards, and good conductors of cold. Thus 

 is the heat absorbed by day, radiated into space by night. Not 

 so with well drained soils, for such retain it for the promotion of 

 the growth of plants. Acids are developed by cold, wet soils, and 

 other compounds, injurious to the healthful condition of growing 

 crops. The mixing of the latest fall of rain with the stagnant water 

 in the soil, causes a mutual decomposition, injurious to vegetable 

 life, checking the growth and diminishing the amount of the crop. 

 These are some of the evils incident upon an excess of water in 

 the soil, which may be removed or cured by under draining, pro- 

 vided there is sufficient fall. 



By drainage the aeration of the soil is greatly promoted. The 

 stagnant water being removed the pores of the soil are open for 

 the reception of atmospheric air, dew or rain water. The union 

 of the elements where combination makes the atmosphere, coming 

 thus in contact with the combined elements that make the soil, pro- 

 duces a change favorable to the growth of plants. This accounts 

 for the increased productiveness of recently drained soil. Latent 

 elements are thus fitted to become the food of the growing crop. 



Kain water is a natural fertilizer, provided it can circulate 

 through and not stagnate in the soil. The introduction of water, 

 says Liebig, is an introduction of alkalies. If so, then it is the 

 cheapest liquid manure the farmer can seize upon. It not only 

 fertilizes, but warms, and cleanses the soil from noxious and dele- 

 terious elements, cari-ying them into the drains, by which the 

 power of soils to absorb aqueous vapor, whether in the form of dew 

 or mist, is greatly increased and made much more productive. 



Says Sir Humphrey Davy, " The power of soils to absorb water 

 from air, is much connected with fertility. When this power is 

 great, the plant is supplied with moisture in dry seasons ; and the 

 eifect of evaporation in the day is counteracted by the absorption 

 of aqueous vapor from the atmosphere, by the interior parts of the 

 soil, during the day, and by both the interior and exterior during 

 the night. Soils most finely comminuted, if underdrained and 

 deeply tilled, are most favorable to this action. 



Thus it is shown what drainage is, what it does, and, therefore, 



