14 PERIODS OP INCREASE AND DECREASE. 





line, between two great basins of rivers, that is crossed by 

 the equator. The river Amazon, according to the informa- 

 tion which I obtained on its banks, is much less regular 

 in the periods of its oscillations than the Orinoco ; it 

 generally begins, however, to increase in December, and 

 attains its maximum of height in March.* It sinks from 

 the month of May, and is at its minimum of height in 

 the months of July and August, at the time when the 

 Lower Orinoco 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 Orinoco have an influence on the Amazon ; 

 but those of the Amazon do not alter the progress of the 

 oscillations of the Orinoco. It results from these data, that 

 in the two basins of the Amazon and the Orinoco, the con- 

 cave and convex summits of the curve of progressive increase 

 and decrease correspond very regularly with each other, 

 since they exhibit the difference of six months, which results 

 from the situation of the rivers in opposite hemispheres. 

 The commencement of the risings only is less tardy in the 

 Orinoco. This river increases sensibly as soon as the sun 

 has crossed the equator ; in the Amazon, on the contrary, 

 the risings do not commence till two months after the 

 equinox. It is known that in the forests north of the line 

 the rains are earlier than in the less woody plains of the 

 southern torrid zone. To this local cause is joined another, 

 which acts perhaps equally on the tardy swellings of the 

 Nile. The Amazon receives a great part of its waters from 

 the Cordillera of the Andes, where the seasons, as every- 

 where among mountains, follow a peculiar type, most fre- 

 quently opposite to that of the low regions. 



The law of the increase and decrease of the Orinoco is 

 more difficult to determine with respect to space, or to the 

 magnitude of the oscillations, than with regard to time, or 

 the period of the maxima and minima. Having been able 

 to measure but imperfectly the risings of the river, I report, 

 not without hesitation, estimates that differ much from each 

 other.f Foreign pilots admit ninety feet for the ordinary 



* Nearly seventy or eighty days after our winter solstice, which ia the 

 lummer solstice of the southern hemisphere. 

 f Tuclcey, Maritime Geogr., vol. iv, p. 309. Hfrpistey, Ezped. to 



