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MEAN ANNUAL ISOTHERMAL LINES. 



230 



annual temperature is the same, we often find great differ- 

 ences in climate ; for there are insular climates in which the 

 seasons are nearly equalised, and excessive climates, as they 

 have been termed, where the temperature of winter and sum- 

 mer is strongly contrasted. The whole of Europe, compared 

 with the eastern parts of America and Asia, has an ' insular ' 

 climate. The northern part of China, and the Atlantic region 

 of the United States, exhibit * excessive climates.' 



We 



Humboldt 



Quebec 



the winter of Petersburg. At Pelun, in China, where the 

 mean temperature of the year is that of the coasts of Brit- 

 tany, the scorching heats of summer are greater than at 

 Cairo, and the winters as rigorous as those of Upsala. 



Mean 



If lines be drawn round the 



lobe through all those places which have the same winter 

 temperature, they are found to deviate from the terrestrial 

 parallels much farther than the lines of equal mean annual 

 heat. The lines of equal winter in Europe, for example, are 

 often curved so as to reach parallels of latitude 9° or 10° 

 distant from each other, whereas the isothermal lines of 

 that continent, or those passing through places having the 



5° 



same mean annual temperature, differ only from 4 to 

 If the reader will turn to the annexed map (fig. 9) by Pro- 

 fessor Dove, he will see that the isothermal line of 32° P., 

 or the freezing point of water, curves so as to vary as much 



as 14 degrees of latitude in passing from east to west, 



or 



to the north of 



from the south of Asiatic Eussia (lat. 56 c 

 Norway (lat. 70°). The same line then trends southward 

 from Norway to Iceland, and passing to the southernmost 

 point of Greenland, in lat. 60°, continues its course south- 



i's Bay, lat. 51° 15', a point 

 more than 18 degrees south of that which it had reached 

 in the arctic sea. It then inclines again northwards through 

 N. America to Behring's Straits. 



Hud so 



The isothermal of 14 



o 



remar 



miles 



south of Yakutsk, lat. 62° 2' north, 

 which lies to the east of the limits of our map,) it inclines 

 northwards to the north of Spitzbergen, in lat. 79°, then 



