Dr. Forry on the Climate of the United States, S^c. 49 



climates, the vernal increase alone often compensates for the low 

 temperature of winter ; for example, although the mean winter 

 temperature at Fort Sullivan is 22°-95, and at Fort Snelling as 

 low as 15°-95, yet that of spring is higher at the latter, being as 

 46^-78 to 40°- 11. Then follows a mean summer temperature 

 more than 10° higher in the excessive than in the uniform clime. 

 The season of autumn, (September, October, and November,) is 

 not perceptibly influenced by these causes. 



These contrasts would be still more striking, were the com- 

 parisons instituted between points on the same isothermal line, 

 instead of the same parallel of latitude; for, as the isothermal 

 curve of Fort Sullivan would strike a point at least 2° north of 

 Fort Snelling, the extremes of the seasons there would be corres- 

 pondently augmented. Sufficient, however, has been adduced 

 to prove that Humboldt's deduction, that the same causes which 

 produce the greatest convexity of the isothermal line, also equal- 

 ize the temperature of the seasons, is unwarranted as a general 

 law. And here the writer may venture to add that these conclu- 

 sions pertain wholly to himself, inasmuch as they had been, 

 doubtless, never brought to the notice of the scientific world, be- 

 fore they were made known by him in his work on " The Cli- 

 mate of the United States and its Endemic Influences." 



These results, in the comparisons just made, appear the more 

 extraordinary, as some reduction of temperature, by reason of the 

 elevation of these interior posts, would be a priori inferred ; for, 

 according to Humboldt, "elevations of four hundred meters, (one 

 thousand three hundred and twelve feet,) appear to have a very 

 sensible influence on the mean temperature, even when great por- 

 tions of countries rise progressively.^^ That high table-lands have 

 a more exalted temperature than isolated mountains of the same 

 height is well known ; for the elevated plains on which the towns 

 of Bogota, Popayan, Gluito, and Mexico are built, have a much 

 warmer climate than they would have, if elevation above the sea 

 were the only element that determines the temperature when the 

 latitude is given. That our western table-lands, rising gradually 

 to the height of eight hundred feet, cause no diminution of tem- 

 perature, has been already abundantly established. 



Without attempting here to explain the diminution of tempe- 

 rature on the summits of high mountains, it may be remarked 

 that these causes cannot be in operation when a large region of 



Vol. xLvii, No. 1.— April-June, 1844. 7 



