186 REACTION OF THE INTERIOR OF THE EARTH 



is termed " cold." I take the difference between the 

 mean temperatures of St. Petersburg (38'1 Fahr.), 

 and the banks of the Orinoco. The purest spring 

 waters that I ever drank while I remained in the 

 district of the Cataracts of Atures and Maypures, ( 255 ) 

 or in the forests of Atabapo, had a temperature of up- 

 wards of 26 Cent, or 78-8 Fahr. And the tempera- 

 ture of the great rivers of tropical South America 

 corresponds to that of these which would in such case 

 be technically called " cold " springs 1 ( 256 ) 



The flowing forth of springs, occasioned by various 

 causes of pressure, and by the interconnection of fissures 

 containing water, is a phenomenon so general over the 

 earth's surface, that at some points it takes place in the 

 highest uplifted mountain strata, and at others at the 

 bottom of the sea. In the first quarter of the present 

 century, Leopold von Buch, Wahlenberg, and I collected 

 numerous results respecting the temperature of springs 

 and the distribution of heat in the interior of the earth 

 in both hemispheres, from the 12th degree of south to the 

 71st degree of north latitude. ( 257 ) The springs which 

 have an " invariable " temperature were carefully dis- 

 tinguished from those which vary with the seasons ; and 

 Von Buch remarked the powerful influence of the dis- 

 tribution of the fall of rain in the course of the year, 

 or the relative frequency and abundance of winter- 

 and summer-rains, on the temperature of the "vari- 

 able springs," which are, generally speaking, the most 

 numerous and widely diffused class of springs. This 

 influence has recently been placed in a clearer light, 

 both in a geographical and hypsometrical view (or 

 according to latitude and to elevation), by de Gasparin, 



