104 Dr Forry on the Climate of the United States. 



climate tlian tliey 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 dimi- 

 nution of temperature, has been already abundantly esta- 

 blished. 



Without attempting here to explain the diminution of 

 temperature on the summits of high mountains, it may be 

 remarked that these causes cannot be in operation when a 

 large region of country rises very slowly and progessively 

 to a height less than one thousand feet. It is only when 

 lands are considerably and suddenly elevated, and exposed 

 to the action of the atmosphere laterally, that a rapid con- 

 duction of heat and rarefaction of the atmosphere can take 

 place. Om* north-western region, in those districts which 

 are remote from the great lakes, so far from causing a dimi- 

 nution of annual temperature, produces, it has been seen, 

 an augmentation. 



In regard to the extremes of heat and cold in the United 

 States, it would be natural to expect that the severest cold 

 would be registered at the most northern, and the greatest 

 heat at the most southern posts. It is now, however, proved, 

 by exact instrumental observations, that this is not the case, 

 as these are situated on large bodies of water ; but that the 

 western stations. Forts Snelling, Gibson, and Council Bluffs, 

 remote from inland seas, are remai'kable for extremes of 

 temperature. It is here that the mei'cury rises the highest 

 and sinks the lowest, while Forts Brady and Mackinac, the 

 most northern stations, as well as those on the southern 

 coast, exhibit a lesser range of thermometer ; and in accord- 

 ance with the same law, we find that the mean summer tem- 

 perature is greater at Augusta, Georgia, than along the 

 coast of Florida. While at Key West, daring a period of 

 six years, the thermometer never rose above 90°, it attained 

 at Council Bluifs, a point 17° 12' farther north, a height 

 every year varying from 102° to 108°. The highest tempe- 

 rature in the shade noted at various posts, was at Fort 

 Gibson, on the 15th of August 183i, being 110\ In Africa, 

 the mercury is sometimes seen at 12.3", and in British India 



