-1859] WRITINGS OF JOSEPH HENRY. 19 



any extended portions of the globe. But thou;:;;h man can- 

 not direct the winds, nor change the order of the seasons, he 

 is enabled, by altering the conditions under which the forces 

 of nature operate, materially to modify the results produced; 

 for example, removing the forests from an extended portion 

 of country exposes the ground to the immediate radiation 

 of the sun, and increases in many cases the amount of 

 evaporation ; in other places it bakes the earth and allows 

 the water to be carried off to the ocean in freshets, and in 

 some instances, in destructive inundations. 



Drying extensive marshes, or the introduction of a general 

 system of drainage, has a remarkable influence in modifying 

 the temperature. The water which would evaporate, and 

 by the latent heat thus absorbed, would cool the ground, ig 

 suffered to pass through it to the drain beneath, and is thus 

 carried off without depriving the earth of a large amount 

 of heat, which would otherwise be lost. Besides this, the 

 removal of forests gives greater scope to the winds, which 

 are hence subjected to less friction in their passage over the 

 earth. 



The whole subject of the removal of forests is one which 

 deserves more attention than it has usually received. In 

 the progress of settlement, it is evident that a great portion 

 of the wooded land of a new country must give place to the 

 cleared field, in order that man may reap the rich harvest 

 of the cereals, which in his civilized condition are necessa- 

 ries as well as luxuries of life; yet the indiscriminate 

 destruction of the forests is of doubtful propriety. By the 

 judicious reservation of trees along the boundaries of cer- 

 tain portions of land, in accordance with the known direc- 

 tion of the prevailing winrl, the climate may be ameliorated 

 witliin a restricted portion of the earth, both for the pro- 

 duction of plants and animals. While in some parts of the 

 country the clearing of nearly all the ground is absolutely 

 necessary for agricultural purposes, in others it ma}'' be 

 profitable to allow forests of considerable extent to remain 

 in their pristine condition. Cases of this kind however can 

 be determined only by the particular climate of each district 

 of the country. 



