CONNECTION BETWEEN FORESTS AND CLIMATE. 221 



CONNECTION BETWEEN FORESTS AND CLIMATE. 



The reciprocal influences that operate between woodlands and cli- 

 mate, appear to indicate a close relation between them. It is observed 

 that certain consequences follow the clearing off of forests, which can 

 scarcely be otherwise regarded than as a direct eftect, such as the 

 diminution of rivers and the drying up of streams and sjirings. Other 

 effects, scarcely less certain, are seen in the occurrence of destructive 

 tloods, and of unseasonable and prolonged droughts, with other vicissi- 

 tudes of climate which it is alleged did not occur when the country 

 was covered with forests. These appear to have been brought about by 

 tbeir removal, and might, in a great degree, be alleviated by the restora- 

 tion of woodlands to a degree consistent with our best agricultural in- 

 terests. 



On the other hand, there are many facts tending to show, that the 

 presence or absence, and the character of forests, are the effect of cli- 

 mate; and that their cultivation generally, or the planting of particular 

 species, is closely dependent upon it. These conditions of climate should 

 be understood before forest-cultivation is attempted. It is also to be 

 noticed that differences of opinion have been expressed among men of 

 science, as to the extent of influence that forests exert upon the climate, 

 and it is quite probable that the advocates of extreme theories may have 

 erred on both sides. But where principles depend upon facts that may 

 be settled by observation, there should be no differences of opinion ; and 

 as there is no fact in this subject that may not be verified or disproved, 

 the existence of such differences only shows the want of accepted evi- 

 dence derived from trustworthy records. 



It is less than ten years, since scientific observations have been under- 

 taken in Europe, with the view of settling these points by carefully 

 noting from instrumental indications the actual conditions of the atmos- 

 phere in the forests as compared with the open fields, and in forests of 

 one kind as compared with another ; and until the present day, we have 

 no observations upon this subject at any point on the American conti- 

 nent that could afford aid by present comparison with these Euro- 

 pean records, or by reference back from any that may be hereafter 

 established. 



Before presenting any of the results thus far obtained at the stations 

 above mentioned, or the methods followed in obtaining them, it may be 

 l)roper to briefly state such facts as are already well proved, and gener- 

 ally admitted, concerning our atmosphere, in reference more particularly 

 to its temperature, and humidity, as they affect, or as they are affected by, 

 forest growth. 



THE ATMOSPHEEE — ITS COMPOIS'ENT PAETS — AQUEOUS VAPOR. 



The atmosphere which surrounds the earth, becomes rarer as we as- 

 cend, and at about the height of 45 miles will, from extreme tenuity, not 

 sensibly refract light. Its weight, as shown by the fluctuations of the 

 barometer, is constantly changing over a given place, being subject to 

 variations dependent upon the daily and annual revolutions of the 

 earth, and to the progress of storms; and as these come to be known, 

 they afford our most certain indications of approaching changes in the 

 weather. The average weight of the atmosphere at sea-level, is about 

 equal to that of a column of mercury 30 inches in height, or 15 pounds 

 to the square inch, or about a ton (2,100 pounds), to a square foot. It is 



