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In order to add a third point of comparison, 

 I shall mention the valley of the Rio Magda- 

 lena, which like the Amazon has one direction 

 only, but unfortunately instead of being that 

 of the breeze it is from south to north. Situate 

 in the region of the trade-winds, the Rio Mag- 

 dalena has the stagnant air of the Upper Oroo- 

 noko. From the canal of Mahates as far as 

 Honda, particularly south of the town of Mom- 

 pox, we never felt the wind blow but at the 

 approach of the storms of night. 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 moun- 

 tains, 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. Every where the unequal heat- 

 ing of the soil, and the proximity of mountains 

 covered with perpetual snows, 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- 



