Field Drainap'e. 



39 



30 degrees. The heat travels through the soil at a rate 

 proportionate to the depth, as will be seen from the following 

 table : — 



Situation of Thermometer. 



Middle of Warm 

 Penod. 



Middle of Cold 

 Penod. 



Mean Kange. 



In the air 



Sunk I mch in ground .. 

 „ 3 feet „ .. ., 



j> ^ j> »» •• •• 

 >> 12 ,, ,, ,. ,, 



9> 24 i9 J> •• •• 



Month 

 July 21 .. ,. 

 July 26 .. 

 August 9.* 

 August 25 

 September 25.. 

 November 30 .. 



Month. 

 January 20 

 January 24 j. 

 February 8 ,. 

 February 24 . . 

 March 27 

 June I 



Degrees. 

 29*8 



25*4 



21*7 



15-4 



9*5 

 3*4 



Thus it will be seen that it takes six months for the alter- 

 nations of heat and cold to affect the soil at a depth of 

 24 feet ; and when it is coldest above ground, the subsoil at 

 this depth below the ground is the warmest, and the heat of 

 the summer sun is gradually ascending through the soil 

 during the winter and early spring months to assist the 

 germination of the seeds sown, and to keep warm the roots 

 of the plants during the snows and frosts of winter.* 



The effect of judicious drainage is to increase the capacity 

 of the soil for absorbing heat, and also to enable it to keep 

 up the temperature of the soil during cold weather* 



Water is a better conductor of heat than air, and thus in 

 cold weather, and when the ground is covered with snow, 

 undrained land, having the crevices or spaces between its 

 particles filled with water instead of air, on the one hand parts 

 with its supply of heat more rapidly than drained land ; and, 

 on the other hand, is less calculated to take in as large a 

 supply in the warm period of the year. 



To prove the effect of drainage in raising the temperature 

 of the earth, a premium was offered by the Marquis of 

 Tweeddale, some years ago, for observations and experiments 

 to be made on soils of a similar character, glowing the same 

 crops, and situated in the same locality ; the result of which 



* Stemmetz, * Sunshine and Showers.' 



