CLIMATE AND FLOEA OF AMAZONIA. 103 



Climate of Amazonia. 



The climate of this region is revealed by the action of the river itself, by the 

 winds checking its current, the periodical oscillations of its discharge, the alter- 

 nating rise and fall of its affluents. A " visible equator," as it has been called in 

 reference to its course, parallel with the line intersecting its basin from the Andes 

 to the Atlantic, the Amazons never leaves the zone in which the north-east and 

 south-east trade winds contend for trhe supremacy. Usually these regular winds 

 penetrate inland no farther than Manaos at the Rio Negro confluence, beyond 

 which the aerial currents become less uniform, being deflected from their normal 

 course by local influences, such as the Venezuelan llanos in the north, the Bolivian 

 and Matto Grosso plains in the south. 



The liffht breeze following: the flow of the Amazons combines with the 

 trades passing higher up to refresh the atmosphere, thus contributing to give the 

 Amazonian lands a far greater relative salubrity than that of many other tropical 

 regions. In Api-il and the beginning of May the '* general" winds, as the trades 

 are called, prevail from Cape S. R,oque to Maranhâo, and are rapidly propagated 

 along the seaboard, following in the wake of the sun on its course to the northern 

 tropic. But on reaching the estuary they are arrested, or at least greatly retarded 

 for a time, perhaps under the influence of the atmospheric current accompanying 

 that of the river, and felt at a distance of 150 or 200 miles from the coast. Thus 

 it happens that the south-east trades sometimes take quite two months to advance 

 from Cape S. Roque to the Orinoco. 



The prevalence of these winds coincides with the dry season from September 

 to January, while the calms correspond with the rainy period from February to 

 July and August. The mean rainfall for the whole basin probably exceeds 80 

 inches, the slight precipitation in the region of the savannas being compensated 

 by the heavy downpours on the eastern slopes of the Andes. But great differences 

 are observed between the climates of the lower and upper Amazonian districts. 

 The latter, being less exposed to the fresh sea breezes, have a greater range of 

 temperature ; the Rio Negro is often swept by fierce gales and here fine and rainy 

 weather follow without much regularity throughout the year. At Para, on the 

 contrary, the seasons are much more sharply defined, despite the slight variations 

 of temperature from month to month.* 



Amazonian Flora. 



The hot and moist Amazonian woodlands rival, and even surpass in their 



immensity the great forest zone of the Congo itself. The selva, that is, the 



thickly wooded region, occupies with little interruption a space estimated at 



about 2,000,000 square miles, or seventeen times that of the British Isles. 



Including the north-eastern tracts on the Guiana seaboard, it extends in a broad 



zone between the Amazons and the savannas, but is interrupted towards the 



* Meteorological conditions of Para in Brazilian Amazonia : — 



Temperature. 



Latitude. Maximum. Mean. Minimum. Eainfall. 



Para. . 1^28'S. 95" Fahr. 82'' Fahr. 72° Fahr. 120 inclies. 



