Br Forry on ihe Climate of the United States. 99 



tei* temperature may differ as much as 11' in latitude, a dif- 

 ference of not more than 5" is found between any two places 

 having an equal annual temperature — disparities which in- 

 crease as the eastern coast of Asia is approached. In the 

 United States the same law obtains ; for between the iso- 

 thermal line of Fort A^ancouver and the same in the Atlantic 

 region, the difference is only 4° of latitude. (See Plate II.) 



The isotheral curves or lines of equal summer follow a 

 direction opposite to that of the isocheimal lines. The 

 region about Moscow and that about the mouth of the Loire, 

 in France, notwithstanding diflFering 11° in latitude, present 

 the same summer temperature. Although this result, as 

 regards difference of latitude, is not discovered in the United 

 States, yet the most extraordinary results in this respect 

 have been demonstrated on the same parallel running from 

 the Atlantic through the great lakes. In the United States 

 the heats of summer are everywhere intense. At Fort 

 Snelling, notwithstanding the isocheimal line is 54° lower 

 than at Key West, the isotheral is only 8° lower. (See 

 Plate II.) At Fort Vancouver, the mean summer tempera- 

 ture is 2° or 3° higher than on the same parallel in the 

 region of the Atlantic and the great lakes, and about 7° 

 lower than in the excessive climates of the same region. In 

 tracing an isothermal line around the globe, we find that the 

 same causes which, on the Atlantic coast of North America 

 and in the noHh of China, depress the curves of equal an- 

 nual heat, tend to elevate the isotheral curves or lines of 

 equal summer. Thus, in following the isothermal line of 

 51 around the globe, and adding the indications of the mean 

 tempei'ature of summer and winter at its summits and 

 depressions, we find it marked in England, e^s^si,; in Hun- 

 gary, ^^; in China, ^i^ ; in Western Amei-ica, at Fort 

 Yancouvei*, ^^^ ; and in eastern America, at Council Bluffs, 

 ■^ ; and at Fort Wolcott, Rhode Island, ^^^^ 



The law, as established by Humboldt, that the same causes 

 which produce the greatest convexity of the isothermal line also 

 equalize the temperature of the seasons, has been already well 

 illustrated in the table tracing the isothermal line of 55°-40 



