THE SOIL 



53 



particles, each contact giving rise to the formation of a concave 

 surface of the water layer, thus determining the movement of 

 water to that part. The number of these re-entering angles 

 or concave surfaces of water will increase with the fineness of 

 subdivision of the soil. At the same time excessive fineness of 



Fig. 5. 



the particles will tend to make the process slower, by increasing 

 the friction ofi*ered to the motion of the water. 



If all the particles are already wet the action described will 

 occur rapidly, but if some of the pai tides are dry, then the 

 action will not occur until the dry particles become wetted by a 

 slow, creeping movement of the water over them. Hence, 

 although stirring a soil increases the rapidity of evaporation 



