589 



rated* with moisture, resting on the forest and 

 on the bed of the river, produce no perceptible 

 mist, it is difficult to attribute this circumstance 

 to the little coolness of the night f. During my 

 abode on the banks of the Oroonoko and the 

 Rio Negro, the water of these rivers was often 

 from two to three degrees hotter than the noc- 

 turnal temperature of the air unagitated by the 

 wind. 



After four hours navigation in going down the 

 Oroonoko, we arrived at the point of the bifur- 

 cation. Our resting place was on the same 

 beach of the Cassiquiare, where a few days 

 before our great dog had probably been carried 

 off by the jaguars. All the researches made by 

 the Indians to discover some traces of this ani- 

 mal were fruitless. The sky remaining cloudy, 

 I waited in vain for the stars, but I repeated the 

 observation of the magnetic dip, which I had 



* See vol. ii, p. 92 ; and p. 85 of the present volume. 



t See the interesting papers of Sir Humphrey Davy on 

 the formation of fogs. (Phil. Trans., 1819, P. I, p. 211.) 

 At the Great Cataracts the air at night was between twenty- 

 seven and twenty-nine degrees, and the water of the Oroo- 

 noko at 27* G 9 ; but on the banks of the Rio Negro, I have 

 seen the cent, thermometer sink at night, in the air, to 22°, 

 and the surface of the river keep at 24°. (See above, p. 

 165 and 344.) Thus at the Lower Oroonoko, east of the 

 mouth of the Apure, where the breeze blows freely, the 

 water of the river is generally at 28° while the nocturnal 

 temperature of the air sinks to 25° or lower. 



