IRRIGATION AND DRAINING. 75 



The dense mass of saturated soil is impervious to air and 

 remains cold and clammy. By draining it below the soil, 

 the warm rains penetrate the entire mass, and there diffuse 

 their genial temperature through the roots. Immediately 

 pressing after these, the warm air rushes in and supplies its 

 portion of augmented heat to the land. Porous soils thus 

 readily imbibe heat, and they as readily part with it; every 

 portion of their own surfaces radiating it when the air in 

 contact with them is below their own temperature. This 

 condition is precisely what is adapted to secure the 

 deposit of the dews, so refreshing, and during a season 

 of drought, so indispensable to the progress of vegetation. 

 Dew can only be found on surfaces which are below the 

 temperature of the surrounding air, and rapid radiation of 

 the heat imbibed during the warmth of a summer's day, is 

 necessary to secure it in sufficient profusion for the demands 

 of luxuriant vegetation in the absence of frequent showers. 



An insensible deposit of moisture precisely analogous to 

 dew, is constantly going forward in deep, rich, porous soils. 

 Wherever the air penetrates them at a higher temperature/ 

 than the soils themselves possess, it not only imparts to them 

 a portion of its excess of heat, but with it also, so much of 

 its combined moisture as its thus lessened capacity for retain- 

 ing latent heat compels it to relinquish. To the reflecting 

 mind imbued with even the first principles of science, these 

 considerations will be justly deemed as of the highest conse- 

 quence to the rapid and luxuriant growth and full develop- 

 ment of vegetable life. 



Another essential benefit derivable from drained lands, 

 consists in the advantageous use which can be made of the 

 subsoil plow. If there be no escape for the moisture which 

 may have settled below the surface, the subsoil plow has 

 been found to be injurious rather than beneficial. By loosen- 

 ing the earth it admits a larger deposit of water, which 

 require.? a longer time for evaporation and insensible drainage 

 to discharge. When the water escapes freely, the use of the 

 subsoil plow is attended with the best results. The broken 

 earth thus pulverized to a much greater depth and incorpora- 

 ted with the descending particles of vegetable sustenance 

 affords an enlarged range for the roots of plants, and in pro- 

 portion to its extent, furnishes thorn with additional means of 

 growth. The farmer thus has a means of augmenting his 

 soil and its capacity for production wholly independent of 

 increasing his superficial acres; for with many crops it mat- 



