The Insalubrity Of The Climate Would Be The Same On The Woody Banks Of The Amazon, If That River, Running Like The Niger From West To East, Did Not Follow In Its Immense Length The Same Direction, Which Is That Of The Trade-Winds.

The valley of the Amazon is closed only at its western extremity, where it approaches the Cordilleras of the Andes.

Towards the east, where the sea-breeze strikes the New Continent, the shore is raised but a few feet above the level of the Atlantic. The Upper Orinoco first runs from east to west, and then from north to south. Where its course is nearly parallel to that of the Amazon, a very hilly country (the group of the mountains of Parima and of Dutch and French Guiana) separates it from the Atlantic, and prevents the wind of rotation from reaching Esmeralda. This wind begins to be powerfully felt only from the confluence of the Apure, where the Lower Orinoco runs from west to east in a vast plain open towards the Atlantic, and therefore the climate of this part of the river is less noxious than that of the Upper Orinoco.

In order to add a third point of comparison, I may mention the valley of the Rio Magdalena, which, like the Amazon, has one direction only, but unfortunately, instead of being that of the breeze, it is from south to north. Situated in the region of the trade-winds, the Rio Magdalena has the stagnant air of the Upper Orinoco. From the canal of Mahates as far as Honda, particularly south of the town of Mompox, we never felt the wind blow but at the approach of the evening storms. When, on the contrary, you proceed up the river beyond Honda, you find the atmosphere often agitated. The strong winds that are ingulfed in the valley of Neiva are noted for their excessive heat. We may be at first surprised to perceive that the calm ceases as we approach the lofty mountains in the upper course of the river, but this astonishment ends when we recollect that the dry and burning winds of the Llanos de Neiva are the effect of descending currents. The columns of cold air rush from the top of the Nevados of Quindiu and of Guanacas into the valley, driving before them the lower strata of the atmosphere. Everywhere the unequal heating of the soil, and the proximity of mountains covered with perpetual snow, cause partial currents within the tropics, as well as in the temperate zone. The violent winds of Neiva are not the effect of a repercussion of the trade-winds; they rise where those winds cannot penetrate; and if the mountains of the Upper Orinoco, the tops of which are generally crowned with trees, were more elevated, they would produce the same impetuous movements in the atmosphere as we observe in the Cordilleras of Peru, of Abyssinia, and of Thibet. The intimate connection that exists between the direction of rivers, the height and disposition of the adjacent mountains, the movements of the atmosphere, and the salubrity of the climate, are subjects well worthy of attention.

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