.?> 



Dr. Forry on the Climate of the United States, fyc. 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 ; 

 bat, 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 bis « Principles of Geology," is unsustained by 

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

 n ca. it is unquestionable that the rapid clearing of the country 



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

 n ot " er words, the extreme temperatures of January and July 



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



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



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

 jnere is no doubt that the climate has become, 

 have said, Mess excessive.'" 



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

 r y J s doubtless to distribute the temperature of the year more tin- 

 dually, thus rendering the seasons more variable; and hence 

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

 gruence, which has been experienced both in this country and 



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

 ^instances, may be explained by reference to the fact that, 



1 e the earth, clothed with forest and covered with snow, is 

 ever frozen, and hence sprouts forth its vegetation as soon as the 

 ° w ^ dissolved in spring; the earth in an open country, on the 



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

 jj ering latent for several weeks a great quantity of caloric. 



,s affords an explanation of the changes of climate referred to 

 Person, Rush, and Williams. If, indeed, the mean annual 



01 «*u, No. 2.-JuJy-Sept. 1844. 31 



as 



»hil 



