A general survey of the continent of America will illustrate the connexion between this law and the subject now before us. In the first place, as regards moisture, all the great rivers in the New World are on the eastern coast, none of them on the western. The causes of this remarkable fact are unknown;173 but it is certain that neither in North, nor in South America, does one considerable river empty itself into the Pacific; while on the opposite side there are numerous rivers, some of enormous magnitude, all of great importance, as the Negro, the La Plata, the San Francisco, the Amazon, the Orinoco, the Mississippi, the Alabama, the Saint John, the Potomac, the Susquehannah, the Delaware, the Hudson, and the Saint Lawrence. By this vast water-system the soil is towards the east constantly irrigated:174 but towards the west there is in North America only one river of value, the Oregon;175 while in South America, from the Isthmus of Panama to the Straits of Magellan, there is no great river at all.
But as to the other main cause of fertility, namely heat, we find in North America a state of things precisely the reverse. There we find that while the irrigation is on the east, the heat is on the west.176 This difference of temperature between the two coasts is probably connected with some great meteorological law; for in the whole of the northern hemisphere, the eastern part of continents and of islands is colder than the western.177 Whether, however, this is owing to some large and comprehensive cause, or whether each instance has a cause peculiar to itself, is an alternative, in the present state of knowledge, impossible to decide; but the fact is unquestionable, and its influence upon the early history of America is extremely curious. In consequence of it, the two great conditions of fertility have not been united in any part of the continent north of Mexico. The countries on the one side have wanted heat; those on the other side have wanted irrigation. The accumulation of wealth being thus impeded, the progress of society was stopped; and until, in the sixteenth century, the knowledge of Europe was brought to bear upon America, there is no instance of any people north of the twentieth parallel, reaching even that imperfect civilization to which the inhabitants of India and of Egypt easily attained.178 On the other hand, south of the twentieth parallel, the continent suddenly changes its form, and, rapidly contracting, becomes a small strip of land, until it reaches the Isthmus of Panama. This narrow tract was the centre of Mexican civilization; and a comparison of the preceding arguments will easily show why such was the case; for the peculiar configuration of the land secured a very large amount of coast, and thus gave to the southern part of North America the character of an island. Hence there arose one of the characteristics of an insular climate, namely, an increase of moisture caused by the watery vapour which springs from the sea.179 While, therefore, the position of Mexico near the equator gave it heat, the shape of the land gave it humidity; and this being the only part of North America in which these two conditions were united, it was likewise the only part which was at all civilized. There can be no doubt that if the sandy plains of California and southern Columbia, instead of being scorched into sterility, had been irrigated by the rivers of the east, or if the rivers of the east had been accompanied by the heat of the west, the result of either combination would have been that exuberance of soil by which, as the history of the world decisively proves, every early civilization was preceded. But inasmuch as, of the two elements of fertility, one was deficient in every part of America north of the twentieth parallel, it followed that, until that line was passed, civilization could gain no resting-place; and there never has been found, and we may confidently assert never will be found, any evidence that even a single ancient nation, in the whole of that enormous continent, was able to make much progress in the arts of life, or organize itself into a fixed and permanent society.
Thus far as to the physical agents which controlled the early destinies of North America. But in reference to South America, a different train of circumstances came into play; for the law by virtue of which the eastern coasts are colder than the western, is not only inapplicable to the southern hemisphere, but is replaced by another law precisely the reverse. North of the equator, the east is colder than the west; south of the equator, the east is hotter than the west.180 If now, we connect this fact with what has been noticed respecting the vast river-system which distinguishes the east of America from the west, it becomes evident that in South America there exists that coöperation of heat and humidity in which North America is deficient. The result is, that the soil in the eastern part of South America is remarkable for its exuberance, not only within the tropic, but considerably beyond it; the south of Brazil, and even part of Uruguay, possessing a fertility not to be found in any country of North America situated under a corresponding latitude.
On a hasty view of the preceding generalizations, it might be expected that the eastern side of South America, being thus richly endowed by nature,181 would have been the seat of one of those civilizations, which, in other parts of the world, similar causes produced. But if we look a little further, we shall find that what has just been pointed out, by no means exhausts even the physical bearings of this subject, and that we must take into consideration a third great agent, which has sufficed to neutralize the natural results of the other two, and to retain in barbarism the inhabitants of what otherwise would have been the most flourishing of all the countries of the New World.
The agent to which I allude is the trade-wind; a striking phenomenon, by which, as we shall hereafter see, all the civilizations anterior to those of Europe were greatly and injuriously influenced. This wind covers no less than 56° of latitude; 28° north of the equator, and 28° south of it.182 In this large tract, which comprises some of the most fertile countries in the world, the trade-wind blows, during the whole year, either from the north-east or from the south-east.183 The causes of this regularity are now well understood, and are known to depend partly on the displacement of air at the equator, and partly on the motion of the earth; for the cold air from the poles is constantly flowing towards the equator, and thus producing northerly winds in the northern hemisphere, and southerly winds in the southern. These winds are, however, deflected from their natural course by the movement of the earth, as it revolves on its axis from west to east. And as the rotation of the earth is, of course, more rapid at the equator than elsewhere, it happens that in the neighbourhood of the equator the speed is so great as to outstrip the movements of the atmosphere from the poles, and forcing them into another direction, gives rise to those easterly currents which are called trade-winds.184 What, however, we are now rather concerned with, is not so much an explanation of the trade-winds, as an account of the way in which this great physical phenomenon is connected with the history of South America.
The trade-wind, blowing on the eastern coast of South America, and proceeding from the east, crosses the Atlantic Ocean, and therefore reaches the land surcharged with the vapours accumulated in its passage. These vapours, on touching the shore, are, at periodical intervals, condensed into rain; and as their progress westward is checked by that gigantic chain of the Andes, which they are unable to pass,185 they pour the whole of their moisture on Brazil, which, in consequence, is often deluged by the most destructive torrents.186 This abundant supply, being aided by that vast river-system peculiar to the eastern part of America, and being also accompanied by heat, has stimulated