166 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



winds of the southern hemisphere as they approach the equator ; 

 and is there any reason for supposing that the atmosphere does 

 not pass freely from ono hemisphere to another? On the con- 

 trary, many reasons present themselves for supposing that it 

 does. If it did not, the proportion of land and water, and 

 consequently of plants and warm-blooded animals, being so 

 different in the two hemispheres, we might imagine that the con- 

 stituents of the atmosphere in them would, in the course of ages, 

 probably become different also, and that consequently, in such 

 a case, man could not safely pass from one hemiisphcre to the 

 other. Consider the manifold beauties in the whole system of 

 terrestrial adaptations ; remember what a perfect and wonderful 

 machine (§ 268) is this atmosphere ; how exquisitely balanced 

 and beautifully compensated it is in all its parts. AYe know 

 that it is perfect ; that in the performance of its various offices 

 it is never left to the guidance of chance — no, not for a moment. 

 Wherefore I was led to ask myself why the air of the south-east 

 la-ades, when arrived at the zone of equatorial calms, should not, 

 after ascending, rather return to the south than go on to the 

 north ? Where and what is the agency by which its course is 

 decided ? Here I found circumstances which again induced me 

 to suppose it probable that it neither turned back to the south 

 nor mingled with the air which came from the regions of the 

 north-east trades, ascended, and then flowed indiscriminately to 

 the north or the south. But I saw reasons for supposing that 

 what came to the equatorial calms as the south-east trade-winds 

 continued to the north as an upper current, and that what had 

 come to the same zone as north-east trade-winds ascended and 

 continued over into the southern hemisphere as an upper current, 

 bound for the calm zone of Capricorn. And these are the prin- 

 cipal reasons and conjectures upon which these suppositions 

 were based : At the seasons of the year when the area covered 

 by the south-east trade-winds is large, and when they are 

 evaporating most rapidly in the southern hemi.sphere, even up 

 to the equator, the most rain is falling in the northern. There- 

 fare it is fair to suppose that much of the vapour which is taken 

 up on that side of the equator is precipitated on this. The 

 evaporating surface in the southern hemisphere is greater, much 

 greater, than it is in the northern ; still, all the great rivers are 

 in the northern hemisphere, the Amazon being regarded as 

 common to both ; and this fact, as far as it goes, tends to corro- 



