M. Kupffer on Iso-geothe'rmal Lines. 25? 



perature of the interior of the earth. The Tyrolese Alps pre- 

 sent every where porphyry and pyroxene, of which their mas- 

 ses are composed. To the south of the equator we have, un- 

 der the second meridian, only one observation, that of Congo ; 

 and, if we may be permitted to draw a conclusion, it indicates 

 that the warmest iso-geothermal line does not coincide with the 

 terrestrial equator. To find a point in the former, we may 

 take the middle of the distance which separates the line at 20°, 

 and the station of Congo, where 22° is the temperature of the 

 ground. If, as may be presumed, this equator runs parallel to 

 the line of 20°, its temperature under the first meridian is 

 greater than that which has been calculated for the ground of 

 the terrestrial equator. It is smaller under the 2d, 3d, and 

 4th. The temperature of the iso-geothermal equator will be 

 more equal than if this line connected with the terrestrial equa- 

 tor, and will nowhere deviate greatly from 22°, the mean tem- 

 perature of these regions." 



M. Kupffer next proceeds to show that his system of Iso- 

 thermal lines ac{;ords with some of the leading facts of physi- 

 cal geography, such as the progress of vegetation in different 

 places, that of the polar ices, and the distribution of terrestrial 

 magnetism. 



" The temperature of the ground," says he, " is connected 

 by different relations with the other great phenomena of our 

 globe. Wahlenberg has already remarked, that the existence 

 in high latitudes of durable vegetables with deep roots, such 

 -as trees and shrubs, can arise only from the temperature of the 

 ground exceeding that of the air. In these latitudes the periods 

 of vegetation appear to follow that of the temperature of the 

 ground almost as much as that of the air. This is an observa- 

 tion which I have often made in my excursion to the north of 

 the Uralian Chain. In middle Russia vegetation commences 

 later than in Germany, but the harvest takes place nearly at 

 the same time, viz. in July. Farther to the north, till the mean 

 temperature is 0° (32° Fahr.) the harvest is later, viz. in Au- 

 gust, or even in the beginning of September. This epoch, which 

 coincides with the maximum of temperature in the air, is con- 

 nected also in liigh latitudes with that of the temperature of 

 the ground. 



