10 ELEMENTS OF AGRICULTURE 



2. Heat. — A stone thrown into a quiet pool of water 

 produces waves, which move rapidly from the place 

 where the stone struck to the shore, where, striking 

 against the grains of sand and soil particles, they shake 

 them about. When sunshine comes to the earth from 

 the sun, it moves in waves just as perfect as those pro- 

 duced in the w r ater. But the waves of sunshine travel 

 very much faster than the waves of water, and are so 

 very small that they cannot be seen. Now, these waves 

 of sunshine coming from the sun strike against the 

 surface of the earth and shake up its very small par- 

 ticles, or molecules, as they should be called, much as 

 the waves in the pool of water shake up the particles of 

 soil on the shore. From the motion produced among its 

 surface molecules the earth becomes warmed. If a crowd 

 of children are all. running about very fast and bumping 

 into one another they soon become quite warm from 

 the violent exercise. So with the small particles or 

 molecules against which the sun's heat strikes; they 

 become much excited, move about very rapidly, bump 

 into one another, and are thus warmed. 



3. Steam. — When a kettle of water is put over a fire 

 to boil, the little heat waves from the fire, which are 

 like those from the sun, first warm up the kettle. When 

 the kettle becomes warm it transfers some of its heat 

 to the water, and so motion begins among the molecules 

 of water. This motion is slow at first, but as the heat 

 waves from the fire continue to strike against the kettle, 

 more and more heat passes through to the water, and 



