SECT, xxvr.] ISOTHERMAL LINES. 297 



Ulea in Lapland, latitude 66, and Table Bay, on the coast 

 of Labrador, latitude 54. 



Thus it appears that the isothermal lines, which are 

 nearly parallel to the equator for about 22, afterwards 

 deviate more and more. From the observations of Sir 

 Charles Giesecke in Greenland, of Captain Scoresby in the 

 Arctic Seas, and also from those of Sir Edward Parry and 

 Sir John Franklin, it is found that the isothermal lines of 

 Europe and America entirely separate in the high latitudes, 

 and surround two poles of maximum cold, one in America 

 and the other in the north of Asia, neither of which coin- 

 cides with the pole of the earth's rotation. These poles are 

 both situate in about the 80th parallel of north latitude. 

 The Transatlantic pole is in the 100th degree of west longi- 

 tude, about 5 to the north of Sir Graham Moore's Bay, in 

 the Polar Seas ; and the Asiatic pole is in the 95th degree 

 of east longitude, a little to the north of the Bay of Taimura, 

 near the North-east Cape. According to the estimation of 

 Sir David Brewster, from the observations of M. de Hum- 

 bold t and Captains Parry and Scoresby, the mean annual 

 temperature of the Asiatic pole is nearly 1 of Fahrenheit's 

 thermometer, and that of the Transatlantic pole about 3^ 

 below zero, whereas he supposes the mean annual tempera- 

 ture of the pole of rotation to be 4 or 5. It is believed 

 that two corresponding poles of maximum cold exist in 

 the southern hemisphere, though observations are wanting 

 to trace the course of the southern isothermal lines with 

 the same accuracy as the northern. 



The isothermal lines, or such as pass through places where 

 the mean annual temperature of the air is the same, do not 

 always coincide with the isogeothermal lines, which are those 

 passing through places where the mean temperature of the 

 ground is the same. Sir David Brewster, in discussing this 

 subject, finds that the isogeothermal lines are always parallel 

 to the isothermal lines ; consequently the same general 

 formula will serve to determine both, since the difference is 



