298 TEMPERATURE OF THE POLES. [SECT. xxvi. 



a constant quantity obtained by observation, and depending 

 upon the distance of the place from the neutral isothermal 

 line. These results are confirmed by the observations of M. 

 Kupffer of Kasan during his excursions to the north, which 

 show that the European and the American portions of the 

 isogeothermal line of 32 of Fahrenheit actually separate, 

 and go round the two poles of maximum cold. This 

 traveller remarked, also, that the temperature both of the 

 air and of the soil decreases most rapidly towards the 45th 

 degree of latitude. 



It is evident that places may have the same mean annual 

 temperature, and yet differ materially in climate. In one, 

 the winters may be mild and the summers cool ; whereas 

 another may experience the extremes of heat and cold. 

 Lines passing through places having the same mean summer 

 or winter temperature are neither parallel to the isothermal, 

 the geothermal lines, nor to one another, and they differ still 

 more from the parallels of latitude. In Europe, the latitude 

 of two places which have the same annual heat never differs 

 more than 8 or 9 ; whereas the difference in the latitude of 

 those having the same mean winter temperature is sometimes 

 as much as 18 or 19. At Kasan, in the interior of Russia, 

 in latitude 55*48, nearly the same with that of Edinburgh, 

 the mean annual temperature is about 37'6 ; at Edinburgh 

 it is 47'84. At Kasan, the mean summer temperature is 

 64-84, and that of winter 2-12 ; whereas at Edinburgh 

 the mean summer temperature is 58'28, and that of winter 

 38'66. Whence it appears that the difference of winter 

 temperature is much greater than that of summer. At 

 Quebec, the summers are as warm as those in Paris, and 

 grapes sometimes ripen in the open air : whereas the winters 

 are as severe as in Petersburgh ; the snow lies five feet deep 

 for several months, wheel carriages cannot be used, the ice 

 is too hard for skating, travelling is performed in sledges, 

 and frequently on the ice of the river St. Lawrence. The 

 cold at Melville Island on the 15th of January, 1820, ac- 



