272 Lieut. Maury on the Probable Relation between 



south ; and from the south side of this belt the air flows in 

 a never-ceasing breeze, called the NE. trade winds, towards 

 the equator. 



On the north side of it, the prevailing winds come from it 

 also ; but they go towards the NE. They are the well known 

 south-westerly winds which prevail along the route from this 

 to England in the ratio of two to one. 



Now these last named winds are going from a warmer to 

 a colder climate ; and therefore it may be supposed that na- 

 ture exacts from them what we know she exacts from the 

 air under similar circumstances, but on a smaller scale be- 

 fore our eyes, viz., more precipitation than evaporation. 



Where then does the vapour, which these winds carry 

 along, come from ? was one of the questions suggested by 

 the charts. 



We saw that the air of which the NE. trade winds are 

 comprised, and which comes out of the same zone of calms, 

 as do these south-westerly winds, so far from being saturated 

 with vapour at its exodus, was dry ; — the NE. trade winds 

 are for the most part dry winds ; — we perceive that going 

 from a lower to a higher temperature their evaporating 

 powers were increased ; and they had to travel in their 

 oblique course, towards the equator, a distance of near 3000 

 miles ; that as a general rule they evaporated all the time, 

 and all the way, and precipitated little or none on their route ; 

 that they were not saturated with moisture until they had 

 arrived fully up to the region of equatorial calms, a zone of 

 constant precipitation. 



This calm zone of Cancer borders also, it was perceived, 

 upon a rainy region. 



Where then does the vapour, which is here on the north- 

 ern edge of this zone of Cancer, condensed into rains — and 

 where also does the vapour which the rain winds that flow out 

 on the polar side of this zone — where ? was the oft-repeated 

 question, — does the vapour which is condensed into rains for 

 the extra tropical regions of the north, come from ] 



It might possibly be taken up by the NE. trade winds ; 

 and it might be the residuum, which, after supplying the 

 equatorial calms witii their rain, was carried up in the 



