EASTING OF THE TEADE- WINDS, ETC. 163 



ihe siirface from warmer to colder regions, it mnst, in this part of 

 its circuit, precipitate more than it evaporates. Now it is a coin- 

 cidence, 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 which 

 they are longest in contact with an evaporating smface ; the route 

 by which all circumstances are most favoiu:able to complete satura- 

 tion ; and this is the route by which they can pass over into the 

 southern hemisphere most hea\'ily laden with vapom-s for the ex- 

 tra-tropical regions of that half of the globe ; and this is the sup- 

 posed route which the north-east trade-winds of the Pacific take to 

 reach the equator and to pass from it. Accordingly, if this pro- 

 cess of reasoning be good, that j)ortion of South America betvreen 

 the calms of Capricorn and Cape Horn, upon the mountain ranges 

 of which this part of the atmosphere, whose circuit I am consider- 

 ing as type, first impinges, ought to be a region of copious pre- 

 cipitation. Now let us turn to the works on Physical Geography, 

 and see what we can find upon this subject. In Berghaus and 

 Johnston — department Hyetography — it is stated, on the autho- 

 rity of Captain King, K. N., that upwards of twelve feet (one hun- 

 <ired and fifty-three inches) of rain fell in forty-one days on that 

 part of the coast of Patagonia which Hes within the sweep of the 

 winds just described. So much rain falls there, navigators say, 

 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 ranges 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 -^A^nds, and the 

 amount of precipitation, may be regarded as evidence afforded by 

 natm-e, if not in favom' of, certainly not against, the conjectm-e that 

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

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

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

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

 suggested, whence these winds could get so much vapoiu\ 



356. Notwithstanding the amount of circumstantial e^adence 

 SJi^two?'?r ' ^% ^^^^ ^^^ already been brought to show that the air 

 air cross ? answered, which the uorth-cast and the south-east trade-winds 

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



M 2 



