10 



country into one covered with trees, at a time when the winter cold is the 

 most severe, he would immediately find a degree of comfort and relief, that 

 renders all arguments needless, to show that deanng away the trees from the 

 land diminishes, the temperature of the gronnd in mnter. It is familiarly known 

 that frost does not penetrate the ground to the same depth in the woods as 

 in the fields. 



Although the thermometer will always exhibit several degrees, often as 

 high as twenty, between the temperature of the thick woods and the open 

 prairies; yet men do not require the delicate sense of the thermometer to 

 teach them this truth ; their own sensation advises them of the change from 

 open grounds to the surroundings of overhanging trees, before they have 

 time to consult the instrument. Cut away these trees and a change must 

 follow the destruction. 



In the state of Michigan it has been found' that the winters have greatly 

 increased in severity within the last forty years, and that this increased se- 

 verity seems to move along even-paced with the destruction of the forests. 

 Thirty years ago the peach was one of the most abundant fruits of that state ; 

 at that time frost, injurious to corn at any time from May to October, was a 

 thing unknown. Now the peach is an uncertain crop, and frost often injures 

 the corn. 



Trees have a power to conduct heat, by which they facilitate its passage 

 from the air to the ground in summer, and from the ground to the air in 

 winter. 



Trees also, like animals, have a specific heat of their own, which aids in 

 equalizing the temperature of the surrounding air. 



For some unexplained reason, connected with vegetable life, trees when in 

 full foliage become cold at night, often colder than the air, which therefore 

 is also cooled by this cause. 

 Forests, by their shade, prevent the radiation of heat from the ground. 

 The evaporation of a large amount of water from the surface of the leaves 

 of trees produces coldness in the air in contact with them. 



It is quite evident, therefore, that a forest is a great equalizer of temper- 

 ature, modifying both the extreme heat of summer and the extreme cold in 

 the winter ; its removal makes the climate more excessive ; the range of the 

 thermometer being increased; and many crops, fruits, &c., that could be 

 raised under the protection of the forests, are killed, either by this excessive 

 heat or extreme cold. 



Humidity. — No constituent of the atmospheric air is more important, or 

 less understood, than aqueous vapor, the greater or less amount of which 

 regulates not only the growth of plants, but also to a considerable degree 

 the health and comfort of the inhabitants. It prevents the undue radiation 

 of heat from the ground, and thus aids materially in maintaining that equit- 

 able degree of temperature so essential to many of the processes of nature. 

 Here again, it will be found upon passing, on a very dry day, from an open 



