THERMAL SPRINGS. 179 



of temperature of one which in another zone, near the equa- 

 tor, Avill be called cold. I may mention the differences be- 

 tween the average temperature of St. Petersburg (38°-12 F.) 

 and of the shores of the Orinoco. The purest spring water 

 which I drank in the vicinity of the cataracts of Atures* 

 and Maypures (81° -14 F.) or in the forest of Atabapo, had 

 a temperature of more than 79° F. ; even the temperature 

 of the great rivers in tropical South America corresponds 

 with the high degrees of heat of such coldf springs. 



* Humboldt, Voyage mix Regions Equinoxiales, t. ii., p. 376. 



f For the sake of comparing the temperature of springs where they 

 break forth directly from the earth, with that of large rivers flowing 

 through open channels, I here bring together the following average 

 numbers from my journals : 



Rio Apure, lat. 7£° ; temperature, 81°. 



Orinoco, between 4° and 8° of latitude; 81°-5— 85°-3. 



Springs in the forest, near the cataract of Maypures, breaking forth 

 from the granite, 82°. 



Cassiquiare, the branch of the Upper Orinoco, which forms the union 

 with the Amazon; only 75°*7. 



Rio Negro, above San Carlos (scarcely 1° 53' to the north of the 

 equator) ; only 74°*8. 



Rio Atabapo, 79° '2 (lat. 3° 50'). 



Orinoco, near the entrance of the Atabapo, 82°. 



Rio Grande de la Magdalena (lat. 5° 12' to 9° 56'), 79° 9'. 



Amazon, 5° 31' S. latitude, opposite to the Pongo of Rentema 

 (Provincia Jaen de Bracamoros), scarcely 1300 feet above the 

 South Sea, only 72°'5. 



The great mass of water of the Orinoco consequently approaches 

 the average temperature of the air of the vicinity. During great in- 

 undations of the savannas, the yellowish-brown waters, which smell 

 of sulphureted hydrogen, acquire a temperature of 92°*8 ; this I found 

 to be the temperature in the Lagartero, to the east of Guayaquil, which 

 swarmed with crocodiles. The soil there becomes heated, as in shallow 

 rivers, by the warmth produced in it by the sun's rays falling upon it. 

 With regard to the multifarious causes of the low temperature of the 

 water of the Rio Negro, which is of a coffee-brown color by reflected 

 light, and of the white waters of the Cassiquiare (a constantly clouded 

 sky, the quantity of rain, the evaporation from the dense forests, and 

 the want of hot sandy tracts upon the banks), see my river voyage, in 

 the Relation Historique, t. ii., p. 463 and 509. In the Rio Guanca- 

 bamba or Chamaya, which falls into the Amazon, near the Pongo de 

 Rentema, I found the temperature of the water to be only 67°"6, as its 

 waters come with prodigious swiftness from the elevated Lake Simi- 

 cocha, on the Cordillera. On my voyage of 52 days up the River Mag- 

 dalena, from Mahates to Honda, I perceived most distinctly, from 

 numerous observations, that a rise in the level of the water was indi- 

 cated for hours previously by a diminution of the temperature of the 

 river. The refrigeration of the stream occurred before the cold mount- 

 ain waters from the Paramos, near the source, came down. Heat and 

 water move, so to speak, in opposite directions and with very unequal 



