42 OP WATER. 



tubes at a convenient depth, so arranged as to receive the 

 superfluous moisture and carry it off. 



128. The effects of drainage may be explained by a 

 comparison. Plants which are kept in flower-pots would 

 soon rot at the root, if the water with which they are 

 watered were left to stagnate in the bottom of the pot 

 without any means of escape. For this reason, the bot 

 tom of the pot has a hole in it, to let the superfluous 

 water run out. Now drainage does the same service for 

 the field that the hole in the bottom does for the earth 

 in the flower-pot. 



129. Drainage produces several other effects, three of 

 which are important. 



(1.) The earth being rendered less moist at the surface, 

 far less evaporation takes place there. Whence, as 

 evaporation always cools the surface very considerably, 

 a drained field keeps in the heat better than one not 

 drained ; and the natural consequence is that the crops 

 ripen earlier. The grain on a drained field is generally 

 fit for the sickle some days, often some weeks, earlier 

 than that on other fields. 



(2.) Lands well drained and deeply tilled bear the 

 drought better than others. The reason of this seems 

 to be, that the pores are always open in deeply tilled, 

 well-drained land, to an unusual depth. Evaporation 

 cannot reach to a great depth, and, in a season of drought, 

 the open pores allow the moisture which lias been kept 

 in the deep earth to rise by capillary attraction. 



(3.) Tho subterranean pipes laid in the earth, open the 

 soil to a freer access of air, allowing it, as it were, to 

 breathe, and receive the benefits of being subjected to the 

 action of the air. The soil is thus rendered fit to absorb 

 and retain the nutritious substances brought into it by 



