UPPER INDIA. 45 



tion of the soil preserve moisture in it. The reason of this, 

 however, does not appear to be so well known as it deserves 

 to be. It has been stated on a previous page that woods and 

 forests preserve moisture, as their leaves falling on the 

 ground retard surface-drainage, and hold water like a sponge. 

 The trees act mechanically as a screen, they prevent the 

 incidence of the sun's rays on the soil, and also break the 

 force of the wind ; thus the two great causes of evaporation 

 are interfered with, and their effects moderated. In the case 

 of lands deeply cultivated, and the soil thoroughly disin- 

 tegrated and pulverized, the action is very similar. The 

 greater part of the rain falling on the surface sinks quickly 

 through the loosened soil, and is temporarily arrested by the 

 soil underlying it, which gradually absorbs it under the pres- 

 sure of gravitation, the remainder being held in the loosened, 

 pulverized soil by capillarity. This water held by capillarity 

 is evaporated by the action of the sun and winds, from the 

 upper loosened soil, and as this becomes dry, it absorbs, by 

 capillary attraction, more moisture from the moist stratum 

 immediately below it. The height to which moisture will 

 rise in loose, open, well-worked soils by capillary attraction 

 is, however, very limited, and the loss from this cause would 

 soon cease or be reduced to next to nothing. But as loss of 

 moisture from this cause diminishes, another comes into 

 operation, the air penetrates the loosened soil, and when 

 in the daytime it becomes heated, it expands, ascends, and 

 carries off moisture in the form of vapour from the depths to 

 which it had penetrated. During the night the reverse takes 

 place ; and as the loosened earth parts with the heat by radia- 

 tion (which it had absorbed during the day) it is moistened by 

 the vapour of water in the air which is condensed in and on 

 it. The soil now, instead of being, as in the case of fields 

 hardened with irrigation, an almost inert mass, has, as it 



