DEEP TILLAGE. 113 



running olT it evaporates, and by this process abstracts a great 

 quantity of heat from the soil and surrounding atmosphere. 

 The evaporation of a pound of water requires about one thou- 

 sand decrees of heat, — some authors stating it less and others 

 more, — or it reduces one hundred pounds of air forty-five dc- 

 grees. This is reversing the experiment of Professor Johnson, 

 in E.?py's " Book of Storms," where he says " a pound of vapor " 

 condensed to water "would heat one hundred pounds of air 

 about forty-five degrees." The ground to a considerable depth 

 is warmer, by many degrees, where the rain is drained oil' in- 

 stead of being allowed to accumulate and evaporate. Hence 

 this enormous loss of an invaluable stimulus to vegetation. 



This chilling and deadly process of evaporation is going on 

 to excess from the time frost comes out of the ground in the 

 spring till freezing again occurs. At this period the undraincd 

 land, having the most water to freeze, becomes the warmest, 

 say in December, when of no value to vegetation, but rather an 

 injury. For once, forsooth, the undrained land is warmer than 

 the drained. But for this excess of heat in winter, this kind 

 of land must pay dearly in early spring. " How is all this ? " 

 inquires the farmer. Simply because water in congealing to 

 either ice or snow has its capacity for heat lessened about one- 

 ninth, and this excess is given off to surrounding bodies; or, in 

 other words, its latent heat is set free. On the other hand, 

 ice, or frost as it is called in the ground, in melting, demands 

 back this same heat, at the rate of from one-eighth to one- 

 ninth of one thousand degrees for every pound melted ; and 

 under the surface it does not obtain all this directly from the 

 sun, but through the soil. Therefore the more water, the cold- 

 er and longer cold will be the land in the spring. Now, let the 

 agriculturist go to work and make this " cold, wet, heavy land " 

 of his the very best he has for any product — trees, vegetables, 

 grains, or grasses. Expense is his next objection. To this 

 we will allude in passing. 



Trenching. — This is understood to be simply inverting the 

 ground to a given depth, without change of material or place, 

 except for the mere facility of the operation. We generally 

 make the trenches three feet wide, and from two to three feet 

 deep, never less than two. The bottom of each, after being 



15* 



