748 



of the Oroonoko and the Amazon furnish a com- 

 bination of circumstances still more extraordi- 

 nary. They are united by the Rio Negro and 

 the Cassiquiare, a branch of the Oroonoko ; it is 

 a navigable line, between two great basins of 

 rivers, that is crossed by the equator. The river 

 Amazon, according to the information which I 

 obtained on it's banks, is much less regular in the 

 periods of it's oscillations than the Oroonoko; it 

 generally begins however to increase in Decem- 

 ber, and attains it's maximum of height in 

 March*. It sinks from the month of May^ 

 and is at it's minimum of height in the months of 

 July and August, at the time when the Lower 

 Oroonoko inundates all the surrounding land. 

 As no river of America can cross the equator 

 from south to north, on account of the general 

 configuration of the ground, the risings of the 

 Oroonoko have an influence on the Amazon ; 

 but those of the Amazon do not alter the pro- 

 gress of the oscillations of the Oroonoko. It 

 results from these data, that, in the two basins 

 of the Amazon and the Oroonoko, the concave 

 and convex summits of the curve of progressive 

 increase and decrease -f* correspond very regu- 

 larly with each other, since they exhibit the dif- 



* Nearly seventy or eighty days after our winter solstice, 

 which is the summer solstice of the southern hemisphere, 

 f Girard, fig. 1. where we find the curve of the rise of th 



