eg THE FIRST BOOK OF FARMING 



HOW SOILS ARE WARMED 



Experiment. Hold your hand in bright sunlight 

 or near a warm stove or radiator. Your hand is 

 warmed by heat radiated from the sun or warm 

 stove through the air to your body. In the same 

 manner the rays of the sun heat the surface of the 

 soil. 



Experiment. Take the stove poker or any small 

 iron rod and hold one end of it in the fire or hold 

 one end of a piece of wire in a candle or lamp flame. 

 The end of the rod or wire will quickly become 

 very hot and heat will gradually be carried its en- 

 tire length until it becomes too hot to hold. This 

 carrying of the heat from particle to particle through 

 the length of the rod is called heating by conduc- 

 tion. Now when the warm rays of the sun reach 

 the soil, or a warm wind blows over it, the surface 

 particles are warmed and then pass the heat on to 

 the next ones below, and these in turn pass it to 

 others and so on till the soil becomes heated to a 

 considerable depth by conduction. 



A clay soil will absorb heat by conduction faster 

 than a sandy soil because the particles of the clay 

 lie so close together that the heat passes more read- 

 ily from one to another than in the case of the 

 coarser sand. 



If the soil is open and porous, warm air and 

 warm rains can enter readily and carry heat to 

 the lower soil. 



You have noticed how a pile of stable manure 



