102 Dr Forry on the Climate of the United States. 



V nearer the equator, which cannot, on the average, cause 

 a greater difference of temperature than l°-50. 



Having thus shewn that there is an actual increase of 

 annual temperature, or a rise of the isothermal line, on re- 

 ceding from the Atlantic, it is deemed unnecessary to give 

 any details proving, that instead of the seasons becoming, 

 from the same causes, more equalized, they actually grow 

 more contrasted, inasmuch as this law has been already 

 abundantly established. Suffice it to compare Fort Snelling 

 on the Mississippi and Fort Sullivan on the Atlantic. Al- 

 though the former has a mean annual temperature 2°"88 

 higher than that of the latter, yet it has a contrast between 

 the mean temperature of winter and summer actually 17°'45 

 greater ! Equally striking is the contrast between the re- 

 sults given by posts on the lakes and those in the same 

 region, notwithstanding not more than one, two, or three 

 hundred miles distant. Thus, on comparing Foi*t Snelling 

 and Howard with positions (Forts Brady and Mackinac) in 

 the modified climate of the lakes, this relation is discovered ; 

 for, although the mean latitude of the latter posts is only 

 1° 34' north of Fort Snelling (and, perhaps, four hundred 

 miles distant), yet the mean annual temperature is 4°-25 

 lower. Now, of this difference in annual temperature, not 

 more than one-half can be accounted for by difference of 

 latitude, being an expression of the same laAv that was re- 

 vealed by the comparison with posts modified by the ocean ; 

 and we also find, that, so far from the temperature of the 

 seasons being more equalized at Fort Snelling, which has a 

 higher annual temperature, the difference between the mean 

 temperatm-e of summer and winter is, in reality, 12°'84 

 greater than on the lakes. 



Humboldt's law holds good so far as the comparison refers 

 to the eastern and western continental coasts, each being- 

 more or less modified by the ocean ; but in a comparison 

 with an interior position remote from large bodies of water, 

 a new element, arising from the law of the accumulation 

 of caloric by the surface of the earth, doubtless enters into 

 the calculation. It may be said, however, that this ought 

 to be compensated by the augmented cold of winter ; but 



