56 CLIMATE AND RESOURCES OP 



so dried and hardened could be ploughed and broken up at 

 any season of the year, which now it cannot be, owing to its 

 hardened condition j and when broken up, it too would fur- 

 ther help to moderate the heat of the hot weather by its 

 increased absorptive and radiative powers. 



It is universally admitted by all physicists that the presence 

 of forests and trees tends to equalize the temperature of a 

 country throughout the year; that the summers are not so 

 hot, and the winters not so cold, as in a country devoid of 

 trees. I have shown how it would affect the summer heat. 

 The chief reasons of the winters not being so cold is the 

 retarded radiation of heat from the ground under the trees, 

 caused by their foliage and branches. When, however, in 

 consequence of the presence of trees, the bare fields were 

 broken up and made absorptive and radiative, it might be 

 considered that the heat caused by arrested radiation from 

 the ground under the trees might be counteracted by the 

 increased radiation from the bare land. This is a problem 

 that has not, as far as I am aware, been solved as yet, and 

 must depend greatly on the relative proportions of the 

 wooded and bare lands. As radiation of heat from the bare 

 lands would be moderated by the amount of vapour in the 

 atmosphere, and the vapour in the atmosphere in dry climates 

 is mainly derived by evaporation from the leaves of trees, 

 it is evident that the greater the proportion of wooded land 

 the less would be the loss of heat by radiation at night from 

 the bare land. 



The greater the proportion of land covered with trees the 

 more will the country be cooled during summer by its effects. 

 If the uncultivated lands now lying useless, and which are 

 obnoxious to the climate, were planted, one of the chief im- 

 mediately remediable sources of heat would be obliterated, 

 and we should in its stead have a source of coolness from thf 



