102 INCREASE OF HEAT. 



and winter, when the air is colder than the soil, is 

 as nothing when compared with the benefits result- 

 ing from it in spring, when the air is warmer, and 

 when the advantages of early growth are great. 

 The most important experiments which we think 

 of as proving the influence of draining upon the 

 temperature of the soil, are those described by Mr. 

 Stephens in his exceedingly instructive book with 

 regard to the operations of the Marquis of Tweed- 

 dale at Tester Mains. There the temperature of 

 the soil in an undrained state was forty-eight de- 

 grees Fahrenheit ; but by the cutting of a drain near 

 it, and the setting in of a current through it, its 

 temperature was raised one and one-half degrees in 

 six hours. 



" Another eifect of water in percolating through 

 the land is seen in the introduction of the atmos- 

 pherical elements which it holds in solution. The 

 carbonic acid, by its operation on the alkalies and 

 alkaline earths, is a powerful solvent and disin- 

 tegrator. The oxygen kee]3s in check the deoxidat- 

 ing eff"ect of vegetable matter in the soil, which in 

 its absence tends to reduce the higher state of 

 oxidation of the iron present in the soil into the 

 lower state, where it does mischief by forming, with 

 acids in the soil, soluble salts, which are injurious 

 to vegetation. 



" But the main purpose served by water during 

 its percolation through the land is that of a feeder 



