90 AGRICULTURE. 



cause of the coldness of these soils is the removal of the 

 water of drainage by evaporation ; Sndly, that their tem- 

 perature is very much raised during the vegetative season 

 of the year by the removal of this water by efficient drain- 

 age ; 3rdly, we will state the reasons for our conviction 

 that, in all soils, the existence of the water-table within 

 less than 4 feet of the surface of the land is prejudicial 

 to vegetation; 4thly, we will show that the water of 

 drainage will be best removed at a reasonable expense, 

 and the level of the water-table will be best reduced by 

 frequent parallel drains of a depth never less than 4 feet ; 

 5thly, that the direction of these drains should, as a general 

 rule, be in the line of steepest descent ; Cthly, that pipes 

 and collars form a better and cheaper conduit than any 

 other which has been hitherto adopted ; and, 7thly, we will 

 give our opinion on the disputed point whether, in the most 

 retentive soils, drains of 4 feet will effectually remove the 

 water of drainage. 



1st. The main cause of the coldness of retentive soils is 

 the removal of water of drainage by evaporation. 



The evaporation of water produces cold : it cools wine ; 

 in hot climates it produces ice. These facts are known to 

 every one. To determine the actual degree of cold pro- 

 duced by the evaporation of one pound of water from soil 

 is rather a complicated, and not a very certain, operation ; 

 but scientific reasons are given for an approximation to 

 this result that the evaporation of one pound of water 

 lowers the temperature of 100 Ibs. of soil 10. That is to 

 say, that if to 100 Ibs. of soil holding all the water which 

 it can by attraction, but containing no water of drainage, is 

 added one pound of water which it has no means of dis- 

 charging except by evaporation, it will, by the time that it 

 has so discharged it, be 10 colder than it would have been 

 if it had the power of discharging this 1 Ib. by filtration ; 

 or more practically, that if rain, entering in the propor- 

 tion of I Ib. to 100 Ibs. into a retentive soil which is satu- 

 rated with water of attraction, is discharged by evaporation, 



