Iviii 



NOTES. 



( 8S8 ) p. 186. In order to compare, in the tropics, the temperature of springs 

 at the points where they issue directly from terrestrial strata, with the tempe- 

 rature of large rivers flowing in open channels, I collect here the following 

 numbers from my journals: 



Rio Apure, lat. 7f, temp. 81. 

 Orinoco, between 4 and 8 lat., temp. 81'5 85'3. 

 Springs breaking forth from granite, in the forest near the cataract 

 of Maypures, temp. 82. 



Cassiquiare, the arm of the Upper Orinoco, which forms the connection 

 with the Amazons, temp, only 75'8. 



Rio Negro, above San Carlos, scarcely 1 53' north of the equator, only 

 74 a 8. 



Rio Atabapo, 79'l. 



Orinoco near the entrance of the Atabapo, lat. 3 50', 82. 

 Rio Grande de la Magdalena, lat. 5 12' to 9 56', temp. 79'9. 

 Amazons, S. lat. 5 31', opposite to the Pongo of Rentema (in the Pro- 

 vincia Jaen de Bracamoros), little more than 1200 feet above the sea, only 

 72-5. 



Thus it appears that the great mass of water in the Orinoco approaches the 

 mean atmospheric temperature of the region around. When great inundations, 

 overflowing the savannahs, take place, the yellow-brown waters, smelling of 

 sulphuretted hydrogen, become heated up to 92-8; I found such a temperature 

 jn the Lagartero, filled with crocodiles, east of Guayaquil. The earth becomes 

 heated, as in shallow rivers, by the effect of the sun's rays. For the many 

 reasons (constantly clouded skies, abundant rains, evaporation from thick forests, 

 and absence of hot tracts of sand on the banks) of the lower temperature of the 

 "coffee-brown waters" of the Rio Negro and the "white waters" of the Cassi- 

 quiare, see my Relat. hist. t. ii. pp. 463 and 509. In the Rio Guancabamba or 

 Chamaya, which falls into the Amazons near the Pongo de Rentema, I have even 

 found the temperature only 67 6; its waters coming down with enormous rapid- 

 ity, out of the high lake of Simicocha, from the Cordillera. During my fifty- 

 two days' voyage up the Magdalena, from Mahates to Honda, I recognised 

 clearly, by means of repeated observations, that a rise of the level of the river 

 could be foretold, some hours previously, from the lowering of the temperature. 

 The cooling of the water took place sooner as the source of the supply of the 

 cold mountain-waters from the Paramos was approached. Warmth and water 

 move, so to speak, in opposite directions, and with very unequal velocity. When 

 the waters rose suddenly at Badillas, the temperature had previously sunk from 

 80-6 to 74 0< 3. As passengers, sleeping at night, with their baggage, on a low 





