surface. Here again we discover the importance of the elliptical form of our planet. These winds are not only created by the unequal exposure to the sun which it causes, but their direction is determined by the different velocities which result from it. If the polar and equatorial velocities were equal, these currents would be simply north and south winds; but the unequal velocity changes them into a north-west and south-west direction. The equatorial portion of the earth's surface has a much greater velocity of rotation than the polar; the polar currents, therefore, are unable to keep up with the equatorial motion. Thus the direction of the north polar current is changed to the southwest, and that of the south-pole to the north-west. The same cause changes the direction of the upper or equatorial currents to the northeast and south-east. They arrive at the north and south with a greater velocity than the earth's surface has at those points, and are therefore in advance of its motion. To this fact we are indebted for the westerly winds of the North Atlantic. The beneficial influences of these regular currents, and of the winds generally, cannot be estimated. Gratuitous accounts of the imaginary and wonderful, such as Doctor Thompson has interwoven with his more serious labors, are wholly unnecessary to excite a proper degree of interest in them; and while such accounts amuse and perhaps interest the general reader, they in some degree retard the progress of science. The winds restore the equilibrium of the atmosphere, upon the disturbance of which they depend; distribute the vapor of the ocean; protect the tropics from the intense heat to which those regions are exposed, and by conveying the heated air and vapor north, greatly modify the climate there. In fact, they effect all the exchanges, and carry out all the compensations on the surface of our planet. By them the burning climate of Africa, south of the equator, is relieved in December, January and February, when under the vertical rays of the sun. During these months, cold currents from the Indies and upper Asia rush in to relieve these regions, while the reverse takes place when India and Asia are heated by the burning sun of the northern summer and Africa is cooled by the southern winter. The winds of the west and south-west, which prevail in the middle latitudes, soften the temperature of the western coasts of Europe and America. The trade-winds, sweeping over the surface of the ocean from the Antarctic regions, first strike the coast of Chili in the parallels of thirty-five degrees south latitude, and advance along the coasts of Peru as far north as Cape Pariña, when they turn suddenly westward, lowering the temperature of the regions through which they pass. Thus, as observed by Von Humboldt in his 'Aspects of Nature,'' the temperature of the Pacific on the coast near Lima is sixty degrees two minutes Fahrenheit, while in the same latitude out of the current it is seventynine degrees two minutes Fahrenheit. This polar current, then, lowers the temperature of the atmosphere through which it passes nineteen degrees Fahrenheit; it must, therefore, have a very considerable effect on the climate of the entire continent. In the equatorial regions, where the course of the temperature and winds is regular, that of the rains is equally so; and instead of seasons of temperature, which are there unknown, the inhabitants draw the distinguishing line between the dry and rainy seasons. Whenever the trade-wind blows with its wonted regularity, the sky preserves a constant serenity and a deep azure blue, especially when the sun is in the opposite hemisphere; the air is dry, and the atmosphere cloudless. But in proportion as the sun approaches the zenith the trade-wind grows irregular, the sky assumes a whitish tint; it becomes overcast; clouds appear, and sudden showers, accompanied with fierce storms, ensue.' In this we cannot fail to recognise a most important arrangement, whatever may be the effect of these inundating rains in engendering the fevers to which the inhabitants are subject. When we recollect the immense influence of an interposing vapor in weakening the intensity of the sun's rays, we may inquire whether the thick vapor in which they are enveloped, at the time when the solar influence is greatest, does not protect them from dangers to be dreaded infinitely more than the endemical fevers, however fatal they may be. It is not in this only that these rains and winds are indispensable, but to the vegetable world. The quantity of vapor in the atmosphere depends on the intensity of the solar rays; it is therefore always more abundant in the tropical atmosphere. This is one of the causes of the luxuriance of the tropical vegetation; but were it not for the almost inexhaustible supply of water deposited in the rivers and lagoons of those regions by the annual rains, the moisture in the atmosphere would be insufficient to supply the vegetable kingdom. A failure of rain in the temperate climates for a few weeks only will cause the greatest injury. Who has not often seen with feelings of sadness the parched and withered vegetation of our own country, in seasons of drought, and watched the approaching cloud with thankfulness of heart? Thus we see the importance of the winds in effecting an exchange of temperature between the equatorial and polar regions, and in modifying the various climates of the earth. But if the capacity of the air were greater than it is, its temperature would be less easily affected by the solar rays, and this circulation, so essential to both hemispheres, partially if not entirely destroyed; while, if the capacity for heat were less, the pleasant and refreshing winds, so important in knitting together the various nations of the earth by the bonds of reciprocal beneficence, would become the most fearful agents of destruction. There is indeed a most intimate connection between the multiplied physical laws with which man has made himself acquainted; a perfect and unbroken chain, extending through and around the wide domain of the infinite CREATOR; and not a link in all this vast chain can be withdrawn or broken without a fearful disturbance of the whole. The winds keep up the circulation in the atmosphere, and restore its equilibrium, and the oceanic currents, which in some degree depend on them, perform the same office for that element. By these currents the exchange of warm and cold water from the differently-heated regions is effected. It is not our object to attempt to trace these or any other phenomena to their primary cause further than it becomes necessary to connect them together and show the mutual adaptation and concurrent action of the whole; much less do we desire to enter on controverted territory for the purpose of disputation; but, with all due respect for authority, we suggest the possibility that too much importance has been given to the unequal temperatures of the tropical and polar seas, in explaining the oceanic currents. Much, undoubtedly, is due to the general tendency of fluids to maintain an equilibrium, but we do not consider this 'the more profound and irresistible cause.' If the rapidity of these deep currents cannot be explained by the motion of the winds, they must result from some cause more powerful than that by which the winds are produced. It is true the sun has a most powerful influence in warming the oceans. Under the equator, the line of constant temperature is seven thousand two hundred feet below the surface. The gulf stream maintains its elevated temperature for more than one thousand feet below the surface. But the atmosphere is more elastic, is easier affected by the solar rays, receives heat, not only from the rays as they pass through it, but by radiation from the earth. The water loses part of the heat it receives by evaporation and radiation, while the depth of the ocean prevents the solar rays from penetrating to the bottom. Thus the line of constant temperature is at variable depths. At fifty-five degrees eighteen minutes, south latitude, longitude one hundred and forty-nine degrees twenty minutes, west, Sir J. C. Ross found it at six hundred fathoms; at forty-nine degrees seventeen minutes, south latitude, longitude one hundred and seventy-two degrees eighteen minutes, west, it sinks to nine hundred fathoms; while at the equator the same distinguished explorer found it at the depth of twelve hundred fathoms. From these examinations he arrived at the conclusion that there is a belt or circle around the earth where the mean temperature of the sea obtains throughout its entire depth, which is about fifty-six degrees fourteen minutes latitude. This, as he observes, constitutes a neutral ground. That portion which is heated by the solar rays imparts heat to the under layers by an exchange of particles. The sun, therefore, cannot act so powerfully and promptly on the oceanic element as on the atmospheric. If then these phenomena result from the same cause, (i. e., a disturbance of the equilibrium of the two elements,) the oceanic currents would not be greater, more powerful or rapid, than the atmospheric currents. But they are, and therefore must have a more profound and irresistible cause' than the mere tendency to restore the equilibrium. For these reasons, we adopt the opinion of Baron Von Humboldt, that the oceanic currents depend conjointly upon various causes; on the tides; the duration and intensity of prevailing winds; the modifications of density and specific gravity which the particles of water undergo, in consequence of differences in the temperature and in the relative quantity of saline contents at different latitudes and depths; and lastly, the horary variations of the atmospheric pressure successively propagated from east to west, and occurring with such regularity in the tropics. These currents have a great influence on the continental climates. The climates of Chili and Peru are, as we have observed, considerably cooled by the Antarctic polar current of wind; but the entire effect is the joint result of the atmospheric and oceanic currents, which rush in from the same point. A branch of the equatorial current, after passing round Guiana and the Caribbean Sea, forces itself in between Cape Catoche and Cuba to the Gulf of Mexico, and after making the circuit of the gulf, passes out between Florida and Cuba, and continues its course under a new name along our coast as far as Newfoundland, elevating the temperature of the whole coast. This current is deflected from that point to the eastward, and finally reaches the coast of Africa. A portion of its warm waters is carried to western Europe by the prevailing winds, and there contributes to soften the climate. These currents are ever active, and contrast strongly with the disturbed waters through which they pass. Guided by some irresistible power, they pursue their course through the agitated element which surrounds them, unmindful of the storms that impede their progress, but cannot defeat their end. By retracing our steps we shall find that the various zones of the astronomical climate are caused by the elliptical figure of the earth, by reason of which the surface is unequally exposed to the solar rays, other elements of course contributing to the result; and that the isothermal, isocheminal and isotheral lines would be uniformly parallel to each other over the whole terrestrial surface, were it not for the division, distribution and contour of the continents, their mountains or reliefs, and the unequal, absorbing and radiating powers of the surface. But as the beauty and fertility of large sections of the globe depend on these special provisions for the advantages which their location otherwise would have denied them, we find they have been provided in the arrangement and adaptations of the fluid and solid portions of the earth. The grand object contemplated by the Infinite Mind is stamped indelibly on every part of the universe, and all the particles, however affected by the laws of matter, contribute to the final result. If a plateau is necessary to water the valley, it rises at the bidding of the ETERNAL. If the geographical form and position of a continent require a mountain-chain to condense the passing vapor, it rises also at the same Almighty bidding. If a gulf is needed to modify the climate of a continent, and counteract the influence of the terrestrial reliefs, the hills are rolled back and the gulf appears. Can it be said that all these local and important agents, acting so harmoniously with the mysterious forces that pervade the universe, are the offspring of chance? that the terrestrial reliefs, acting so variously on the local climates, on which so much of life and beauty depend, are the accidental result of indeterminate internal powers? The mind is not so much affected by the grandeur of any single phenomenon, however important, as it is by the harmonious action of different and apparently conflicting elements. It is this intimate and indispensable relation which exists between the greatest and the smallest of created beings; between the animate and inanimate worlds; this action and reaction upon each other, by which the end is accomplished; and the special provisions, modifying or wholly defeating the action of general laws, where the interests of our species require it, that tend most strongly to direct the inquiring mind upward to the INFINITE and ETERNAL for a revelation of the hidden cause. But if we look at the general result of the division of the earth's surface into zones of temperature, we shall find a most favorable condition. The torrid zone stretches from the equator to the tropics, embracing an area of seventy-seven million seven hundred thousand square miles; the temperate zones, extending from the tropics to the polar circles, embrace fifty million square miles in each hemisphere; making together one hundred millions of square miles. This area embraces at least three-fourths of the continental element. The frozens contain only eight millions of square miles each; and even this small circle is inhabitable. Owing to the compensations in Sweden, the cereals are cultivated beyond the polar circle. Less therefore than one eleventh part of the earth's surface is beyond the vivifying influence of the solar rays. And we have seen how small a portion of the continental mass is exposed to the vertical rays of the sun when at its highest point, and how that portion is partially protected by the interposing mists and clouds, caused by a rapid evaporation; by the isolated mountain peaks, from which the cold air rushes down; the general elevation; and the luxuriant vegetation, which keeps the atmosphere more humid, and cools the surface of the earth by its moisture and shade. It appears then, from the view we have taken, that the powers by which the continents have been thrown up to their present positions have acted uniformly in every instance; that the local reliefs are necessary where they are found; that the astronomical climates have been variously modified by these agents; and that the elements act in harmony with each other, however widely separated or discordant they may appear; that through the laws of expansion and contraction, of heat and cold, the sea cools the climate of the torrid zone, and warms it in the cold temperate and frigid zones; that the continents are nar row and greatly elevated, with vast isolated peaks, in the equatorial regions, and low and divided, cut up by bays and inland seas, in the higher latitudes; and that the climates depend on the concurrent action of these agents or elements. One irregular or convulsive motion of the mighty upheaving internal power, by which it is supposed the terrestrial reliefs and continental elevations have been produced, would unsettle the physical relations which exist, and more or less disturb the harmonious action of the varied forces of nature. Now bright beneath them gleamed the sun-touched vale, The wife gazed tearless, and her infant son As if she felt, wherever doomed to roam, . With him and with his sire-there would be home. |