40 The Drainage of Fens and Low Lands, 



was a collection of carefully prepared and thoroughly re- 

 liable observations, from which the following results are 

 culled. That during a long-continued frost the mean tem- 

 perature of drained land at 30 in. below the surface was 

 nearly i\ degree warmer than the undrained. That showers 

 of sleet and cold rains lowered the temperature of drained 

 lands 2 degrees, and undrained land 4 degrees. That in 

 every instance drainage gave a decided advantage in an in- 

 crease of temperature, except only m summer, when a heavy 

 fall of rain was found to lower the temperature of the drained 

 land I degree more than the undrained — an evident advan- 

 tage to a hot, parched soil 



Experiments also made by Dn Madden led him to the con- 

 clusion that an excess of water in the soil reduced its tempe- 

 rature in summer 6| degrees, which amount he considered 

 equivalent to an elevation above the level of the sea of 1959 

 feet So that, supposing two fields, lying side by side, 

 the one drained, the other undrained, and supposing them 

 both equally well cultivated, there would be nearly as much 

 difference in the amount and value of their respective crops 

 as if the drained one was situated at the level of the sea and 

 the other on an elevation as high as the Pentland Hills,* 

 Dr. Madden also, in order to dispel the idea where it existed, 

 that the interstitial spaces being so minute that their contents 

 could be of no consequence, quotes the fact that in moderately 

 well-pulverised soil they amount to no less than one-fourth of 

 the whole bulk of the soil itself; for example, 100 cubic 

 inches of moist soil contain no less than 25 cubic inches of 

 air. According to this calculation, in a field pulverised to the 

 depth of 8 in., every acre will retain beneath its surface no 

 less than 12,545,280 cubic inches ; and for every extra inch 

 in depth the ground is cultivated, 235 tons of additional 

 soil are called into activity, and rendered capable of retaining 

 beneath its surface 1,568,160 additional cubic inches of air. 

 * Lecture on Agricultural Science by Di. Madden. 



