Page:Physical Geography of the Sea and its Meteorology.djvu/192

166 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 one hemisphere to another? On the contrary, 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 constituents 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 hemisphere 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. We 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 principal 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 hemisphere, even up to the equator, the most rain is falling in the northern. Therefore 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