EASTING OF THE TRADE-WINDS, KTC. 169 



trade-winds of that region. To make this clear, see Plate VII., 

 on which I have marked the course of such vapour-bearing 

 wdnds ; A being a breadth or swath of winds in the north-east 

 trades ; B, the same wind as the upper and counter-current to 

 the south-east trades ; and C, the same wind after it has de- 

 scended in the calm belt of Capricorn, and come out on the 

 polar tide thereof, as the rain winds and prevailing north-west 

 winds of the extra-tropical regions of the southern hemisphere. 

 This, as the north-east trades, is the evaporating wind. As the 

 north-east trade-wind, it sweeps over a great waste of waters 

 l^dng between the tropic of Cancer and the equator. Meeting no 

 land in this long oblique track over the tepid waters of a tropical 

 sea, it would, if such were its route, arrive somewhere about the 

 meridian of 140° or 150° west, at the belt of equatorial calms, 

 which always divides the north-east from the south-east trade- 

 winds. Here, depositing a portion of its vapour as it ascends, 

 it would, with the residuum, take, on account of diurnal rotation, 

 a course in the upper region of the atmosphere to the south-east, 

 as far as the calms of Capricorn. Here it descends and continues 

 on towards the coast of South America, in the same direction, 

 appearing now as the prevailing north-west wind of the extra- 

 tropical regions of the southern hemisphere. Travelling on 

 the surface from warmer to colder regions, it must, in this part 

 of its circuit, precipitate more than it evaporates. Kow it is a 

 coincidence, at least, that this is the route by which, on account 

 of the land in the northern hemisphere, the north-east trade- 

 winds have the fairest sweep over that ocean. This is the route 

 by w^hich they are longest in contact with an evaporating- 

 surface ; the route by which all circumstances are most favour- 

 able to complete saturation ; and this is the route by which they 

 can pass over into the southern hemisphere most heavily laden 

 with vapours for the extra-tropical regions of that half of the 

 globe; and this is the supposed route which the north-east 

 trade-winds of the Pacific take to reach the equator and to pass 

 from it. Accordingly, if this process of reasoning be good, that 

 portion of South America between the calms of Capricorn and 

 Cape Horn, upon the mountain ranges of which this part of tho 

 atmosphere, whose circuit I am considering as type, first im- 

 pinges, ought to be a region of copious precipitation. Kow let 

 us turn to the works on Ph^^sical Geograpliy, and see what we 

 can find upon this subject. In Berghaus and Johnston — depart- 



