§ 356. EASTING OF THE TRADE-WINDS, ETC. 1^5 



winds just described. So much rain falls there, navigators sa}^ 

 that they sometimes find the water on the top of the sea fresh and 

 sweet. After impinging upon the cold hill-tops of the Patagonian 

 coast, and passing the snow-clad summits of the Andes, this same 

 wind tumbles down upon the eastern slopes of the range as a dry 

 wind ; as such, it traverses the almost rainless and barren regions 

 of cis- Andean Patagonia and South Buenos Ayres, Plate YIII. 

 These conditions, the direction of the prevailing winds, and the 

 amount of precipitation, may be regarded as evidence afforded by 

 nature, if not in favor of, certainly not against, the conjecture that 

 such may have been the voyage of this vapor through the air. At 

 any rate, here is proof of the immense quantity of vapor which 

 these winds of the extra-tropical regions carry along with them 

 toward the poles ; and I can imagine no other place than that 

 suggested, whence these winds could get so much vapor. 



3o6. Notwithstanding the amount of circumstantial evidence 

 The question, How that has already been brought to show that the air 



caa two currents of, ^ ^ ^ ^ . 



air cross? answered, wuich the nortucast and thc southcast trade-wmds 

 discharge into the belts of equatorial calms, does, in ascending, 

 cross — that from the southern passing over into the northern, and 

 that from the northern passing over into the southern hemisphere 

 (see 0, Q, E, S, and D, E, F, Gr, § 215) — yet some have implied 

 doubt by asking the question, "How are two such currents of air 

 to pass each other?" And, for the want of light upon this point, 

 the correctness of my reasoning, facts, inferences, and deductions 

 have been questioned. In the first place, it may be said in reply, 

 the belt of equatorial calms is often several hundred miles across, 

 seldom less than sixty; whereas the depth of the volume of air that 

 the trade-winds pour into it is only about three miles, for that is 

 supposed to be about the height to which the trade- winds extend. 

 Thus we have the air passing into these calms by an opening on 

 the north side for the northeast trades, and another on the south 

 for the southeast trades, having a cross section of three miles ver- 

 tically to each opening. It then escapes by an opening upward, 

 the cross section of which is sixty or one hundred, or even three 

 hundred miles. A very slow motion upward there will carry off 

 the air in that direction as fast as the two systems of trade-winds, 

 with their motion of twenty miles an hour, can pour it in ; and that 

 curds or flakes of air can readily cross each other and pass in 



