UPPER INDIA. 55 



prevent its becoming heated ; they also absorb heat during 

 the day, which they give off by radiation at night, and they 

 transpire from their leaves the moisture which they imbibe 

 by their roots from the lower-lying moist strata of the earth, 

 which in the form of vapour in the atmosphere moderates 

 the amount of solar heat falling on the ground. 



Supposing the country to be divided like a chess-board, 

 the squares of say a mile each in measurement, the black 

 squares planted with trees and bushes, and the white squares 

 left bare for cultivation, arable land, the planted squares 

 would absorb a great amount of the solar heat which fell on 

 them, and the air in the daytime above them would not be 

 so hot as that coming in contact with the surface of the bare 

 squares. The cooler air over the planted squares would by 

 its greater gravity sink and displace the air over the bare 

 squares as it became heated and expanded. At night, the 

 heat absorbed by the planted squares during the day would 

 be given off by radiation, the superincumbent air would be 

 chilled, sink, and spread over the surface of the bare squares, 

 displacing the more heated air which had not been chilled by 

 radiation. The trees on the planted squares would act me- 

 chanically in checking and breaking the force of the wind, 

 as a lattice-work breakwater breaks the force of the waves ; 

 they would also deflect the wind upwards ; it would not sweep 

 over the surface of the bare squares as it does over a plain 

 where there is nothing to check its force, and its drying 

 effects would be lessened. The surface-soil of the bare squares 

 would not be so dried and hardened from the action of the 

 wind as the open plain now is ; the air would contain more 

 vapour of water evaporated from the trees of the planted 

 squares ; and this again would interpose a screen which 

 would lessen the amount of solar heat falling on the surface 

 of the bare squares. The soil of the bare squares not being 



