96 HANDT-BOOK OF HUSBANDRY. 



roots of plants, and to produce beneficial changes in the mineral 

 ingredients of the soil. 



The rain which falls, finding the soil in a porous condition, 

 sinks into it, and gives up the gases which it contains, passing out 

 of the drains, nearly pure ; while, if the land were already satu- 

 rated, or had %not been made porous by the process of draining, 

 the water would, to a greater or less extent, run off over the 

 surface, and instead of enriching the soil, would carry away some 

 of its more fertile parts. 



3. It warms the lower portions of the soil. We have already 

 seen (i) that the air which circulates in the soil gives up heat, 

 and it thus elevates the temperature of those parts which are 

 cooler than the atmosphere. The water of rains also, in passing 

 down through the soil, carries with it the heat of the surface, 

 and deposits it, and a portion of the heat which it received from 

 the warm air through which it fell, in the lower and cooler parts 

 of the soil. In hot weather, the water which issues from the 

 mouth of a drain is often ten degrees cooler than that which 

 falls on the surface, and all of its lost heat has been given to the 

 soil. 



4. It lessens the cooling of the soil by evaporation. This is one 

 of the most important effects of draining. When liquid water 

 becomes vapor, it increases in bulk 1723 times, and it contains 

 1723 times as much heat. The heat required to evaporate it, is 

 taken from surrounding substances. When water is sprinkled on 

 the floor, it cools the room, because in becoming a vapor (drying) 

 it takes heat from the room. If a wet cloth be placed on the 

 head, and the evaporation of its water assisted by fanning, the 

 head becomes cooler — a portion of its heat being taken to convert 

 the water into the condition of vapor. 



The same action takes place in the soil. When the evapora- 

 tion of its water is rapidly going on, bv the aid of the sun and 

 wind, heat is abstracted and the soil becomes cold. If the water 

 of the soil is mainly removed by draining, there is comparatively 

 little to be evaporated, and comparatively little heat is taken 

 away — probably not more than is received from the atmosphere, (3.} 



