Reflections following the visit to the Galapagos (2)
Striking instances of the manner in which high land deprives air of its moisture may be seen at the Galapagos. Situated in a wind nearly perennial, those sides only which are exposed to it (the southern) are covered with verdure, and have water: all else is dry and barren, excepting such high ground as the passing clouds hang upon indolently as they move northward. In a similar manner may we not conclude that western Peru is deprived of rain—since the easterly trade wind which carries moisture, and consequent fertility, to eastern Peru, is drained, or dried, as it crosses the Andes? And may we not extend this reasoning to other countries similarly situated, such as Patagonia, perhaps Arabia, and even Africa, upon whose arid deserts no moist wind blows? Currents of air, moving from ocean to land, convey vapour; but as these currents pass over high land, or even a considerable extent of low country, much if not the whole of their aqueous contents is discharged, and until such a body of air has again acquired moisture, it is found to be dry, parching, and unfavourable to vegetation.