Dr. Forry on the Climate of the United States, Sec. 237 



places thaws to the depth of four feet, and in the woods to the 

 depth only of two. Moreover, it has been determined by ther- 

 mometrical experiments, that the temperature of the forest, at the 

 distance of twelve inches below the surface of the earth, is, com- 

 pared with the adjacent open field, at least 10° lower, during the 

 summer months ; while no difference is observable during the 

 season of winter. 



" The mere effect of cultivation," as Dr. Traill very correctly 

 observes, "can never be very considerable in changing a climate ;" 

 but, although cultivation of the soil may not be productive of a 

 sensible change in the mean annual temperature, yet such a mod- 

 ification in the distribution of heat among the seasons may be 

 produced, as will greatly influence vegetation. 



Although upon all subjects connected with natural phenomena, 

 there is no higher authority than Charles Lyell, Esq., yet his un- 

 qualified decision of this question, as exhibited in the following 

 quotation from his "Principles of Geology," is unsustained by 

 any well observed facts : — " In the United States of North Ame- 

 rica, it is unquestionable that the rapid clearing of the country 

 has rendered the winters less severe, and the summers less hot ; 

 in other words, the extreme temperatures of January and July 

 have been observed from year to year, to approach nearer to each 

 other. Whether in this case, or in France, the mean tempera- 

 ture has been raised, seems by no means as yet decided : but 

 there is no doubt that the climate has become, as Buffon would, 

 have said, 'less excessive.' " 



Contrary to Mr. Lyell's opinion, one effect of clearing the coun- 

 try is doubtless to distribute the temperature oi the year more un- 

 equally, thus rendering the seasons more variable ; and hence 

 causing, by the exposure of fruits to spring frosts, a serious incon- 

 venience, which has been experienced both in this country and 

 in Europe. The reason of late and variable springs, under these 

 circumstances, may be explained by reference to the fact that, 

 while the earth, clothed with forest and covered with snow, is 

 never frozen, and hence sprouts forth its vegetation as soon as the 

 snow is dissolved in spring ; the earth in an open country, on the 

 other hand, requires, after the snow is melted, to be thawed, thus 

 rendering latent for several weeks a great quantity of caloric. 

 This affords an explanation of the changes of climate referred to 

 by Jefferson, Rush, and Williams. If, indeed, the mean annual 



Vol. XLVii, No. 2.— JuJy-Sept. 1844. 31 



