THE SOIL. 19 



to stand erect any longer, but will soon lose its 

 entire hold, and drift down the current to lodge 

 against some neighbor's cross fence. In a similar 

 manner full grown trees have been dug out and 

 can be seen floating down our large rivers in times 

 of high water. 



MOVEMENTS OF WATER IN THE SOIL. 



On dipping a marble, a pebble, or a pencil in 

 water it will be seen, on taking it out, that a thin 

 film of water adheres to it. A dry pebble, touched 

 against the one already wet, will take part of the 

 water film away from the first one; and a third, 

 touched against the second, will do likewise; and so 

 on, each taking a part of the water and holding it 

 to itself. A force within the earth, called gravity, 

 pulls everything downward; but each little grain of 

 soil has a power within itself which acts against 

 gravity, and keeps a part of the rain falling upon 

 the earth from escaping too fast. This power that 

 pebbles, grains of sand, particles of fine earth, and 

 a great many other things have of drawing a film 

 of water around themselves is called surface ten- 

 sion, or capillarity. It is a force just as truly as 

 gravity is, and plays a very important part in agri- 

 culture. 



It will be found, however, that those same things 

 whicli were covered with this thin film of water, 

 will, if left exposed to free air for a short time, lose 

 the water adhering to them and become pert^c'.ly 



