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worla.mc life; it is ever is the univer

In proving the identity of electricity and magnetism, Erstedt, Ampere, and Faraday have made for science a long stride toward unity. They have simplified nature, according to the energetic expression of M. Babinet. “Electricity,” says this ingenious savant, “is the universal agent of organic and inorganic life; it is everything.” “It is the soul of the physical world,” adds M. Becquerel.

Electricity, magnetism, heat, light, like the sphinx, propose their enigmas to the Edipi of science, who, little by little, penetrate the mysterious meaning, and are already catching vague glimpses of the unity of all.

Truly, every step that science advances, every new discovery that is made in the domain of the physical world, brings more clearly to view the unity of the force that presides over the changes of nature. If, as M. Dumas thinks, and with him many other wise men, the physical world originates from a single element, (hydrogen, according to the Englishman, Prout; an unknown body of half the weight of hydrogen, according to M. Marignac;) if also, as science supposes, this unique element is submitted to a single force, what admirable simplicity shines forth, then, in the creation! What an astonishing variety, in the effects, is produced by the combination of these two causes. The day will come, without doubt, when science will place in brighter light these two equally astonishing marvels. Kepler saw the dawn of this memorable day when he said, “God being an Intelligence unique and universal, the character of the laws which he has imposed upon the world ought to be unity and universality.”

However it may be, solar heat, together with electricity, appears to play an important part in the formation and direction of the winds. At length, in the eighteenth century, Halley assigned the daily heat as a cause for the trades. In the equatorial regions the sun heats the air to such a degree that a continued ascending current is there produced, carrying pact of the sun upon cosmical matter scattered through space under the form of shooting stars, balls, comets, and zodiacal lights. But the greater number see in the sun an electrical battery of increasing activity. M. Geniller, of Liége, among others, thinks that the development of the cloudlike covering which, according to Herschel and Arago, covers the nucleus of the sun, gives rise to torrents of static electricity, whose constant discharges cause the solar light, and thus this body shines by virtue of a permanent electrical storm.

into the higher regions the hot air, which is lighter, from the same cause that makes the heated air and smoke from the fires wo kindle ascend in a vertical column. To fill the void thus caused two currents of colder air from the north and the south rush in, which, heated in their turn, are continually lifted into the upper regions. There is thus a constant coming and going; an equilibrium constantly being broken up and re-established. For above these surface-currents, drawn toward the equator, there is necessarily a double higher and opposite current, carrying to the north and the south the superabundance of air that without it would accumulate over the line.

It is to this same cause that we should attribute the breeze called the sea-breeze, which blows on our coasts during the day, and the land breeze, which prevails during the night. During the day the land, heating more promptly than the sea, makes above itself a stratum of hot air incessantly replaced on the surface by a current of colder air coming from the sea. During the night the land, more prompt to grow cold by radiation, sends, in its turn, a current of cold air toward the sea, above which the heated air is continually lifted. The typhoon and the waterspouts, so terrible always in the Indian Ocean, boiling under a vertical sun, are only the effects of the same cause; that is to say, the ascending whirlwinds of heated air that carry along with irresistible power everything that is caught in their fearful spirals. *

Besides the part that the winds play in maintaining the equilibrium of the air, they act, in a not less interesting and wonderful manner, as vehicles of rain, and as agents prepared for the irrigation of our globe.

It is here that the wisdom of Providence shines forth in all its splendor. Maury divides the winds into two classes: the dry or evaporating winds, (these are the trades ;) and the moist or precipitating winds, (these are the free winds.) The first,

* It is useless to add, that the circulation of the atmosphere does not prevent in reality all the regularity of this system. Without speaking of unknown causes of disturbance, the rotation of the earth and the different phases that its surfaco presents, (mountains, deserts now hot, now cold, etc.,) exercise a constant influence upon the direction of the currents. The typical winds of Maury are those that blow over the ocean, where the nearly level surface offers less resistance to the regularity of their course. The oceanic is to the land surface as twenty-seven is to ten.

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) Atmospheric and Oceanic Currents. 213 blowing over the intertropical regions, imbibe, as a dry sponge, the vapors produced by the solar heat; for, under these boiling latitudes, the evaporating power of the sun is such that it is supposed a liquid stratum of fifteen feet in depth is evaporated annually. In certain seas, such as the Indian Ocean, this stratum attains a depth of twenty feet. Charged with the vapors of the southern hemisphere, the south trades carry them above the calms of the equator and tropic of Cancer to the regions of free winds or precipitants, which, taking them up in their turn, carry them toward the north, until the cold, operating upon the air, presses from it the water which it contains and causes it to fall in rain. The trades of the north transport in a similar manner the vapors of the northern hemisphere to the southern.

Thus is solved the problem of which science has in vain, until now, sought the solution. The northern hemisphere presenting to the solar rays, in the region of the trades, a water surface about a third smaller than the southern, and, in the mean time, receiving a quantity of rain one third greater; all is explained by the exchange of vapors effected between the two hemispheres.

Thus, by a wonderful harmony, a drop of water, drawn from the ocean in the form of vapor by a ray of the sun, courses through the air on the wing of the winds, and in distant places falls as rain on the land which it fertilizes, then, borne in the current of the stream, it reaches the ocean again from which it came, to begin once more the circle of these changes. *

The theory of precipitation is known. The air, forced by some cause to elevate itself, becomes lighter than the column at that time above it, and consequently dilates; then, as it ascends it becomes colder, and the watery vapors that it con

* The equatorial zone is the grand laboratory in which the winds and the rains are formed. This zone, as well as the two bands of tropical calms, is as a thick arch of vapor, which, being in excess, forms almost continued rains. The zone of equatorial calms is not unchangeable; oscillating from the south to the north and from the north to the south of the line, according to the seasons and the position of the sun in the ecliptic, its change makes the rainy and the dry seasons by turn in the intertropical regions. The countries under the equator have the band of equatorial calms to pass over them twice, and consequently have two seasons of rain. The climate of Santa Fe de Bogota is an example of this phenomenon.

FOURTH SERIES, VOL. XIII.-14

tains, condensed by the cold, fall in the form of rain. The proportional cooling of the air is about 370 Fahrenheit to every six hundred and fifty-six feet of elevation. It is on this account we say, that the forests draw the rain ; the barrier that they oppose to the currents on the surface forces them to a higher elevation, and consequently deprive them of the vapors that they hold in suspension. From which it happens that in Egypt, where rains were formerly unknown, they have become relatively abundant since trees have been planted. What cause renders the basin of the Meuse so abundant in water, yet of such inconsiderable extent, but the forests that cover it?

As a consequent of what precedes it must be established as a principle, that the configuration of the earth and the prevailing winds determine the natural irrigation of a country. The flow of water represents the excess of precipitation over evaporation.*

The quantity of annual rain in France is about 353,165 cubic feet per hectare, [the hectare is two acres, one rood, and thirty-five perches ;] this quantity for the whole world amounts to the enormous sum of 27,401,286,824 cubic feet, say 75,072,018 a day. Suppose that rain falls on the Atlantic to the depth of 0.081 feet, the surface being about 25,000,000 square miles. The weight of this water would be about 1,800,000,000 tons, and the salt that it leaves by evaporation would not weigh less than 80,000,000 tons, tenfold the weight that the navies of the whole world could float: If, as may be supposed, in place of a hypothetical depth of 0.081 feet, the volume of water that annually falls on the Atlantic is in reality 4.88 feet, to what a formidable amount will we arrive? What must be the disturbing power of such evaporation and precipitation ?

By a wonderful foresight the northern hemisphere, which contains three fourths of the habitable portion of the world, is that for which the winds are charged to afford the most abundant rain, at the same time fertilizing the earth and creating the thousand streams that form the watercourses and constitute the natural channels of communication between its different parts.

* The air saturated with watery vapor and that in which this moisture is ab. sent, is equally injurious to mankind. The first constitutes the atmosphere of the hot and moist places; it is the malaria of Marennes and the Pontine Marshes, which every year besieges more and more closely the Eternal City, and threatens to invade it with its marshy poisons. The second is the Simoon and Khamsin of the desert. The atmosphere of misty England is almost completely saturated with water, that of France holds a just mean. What moral phenomena are explained by this simple physical fact.

What may we not say concerning the influence exerted by the winds in forming the streams?

Every watercourse supposes a prevailing wind that feeds it. Let us follow, for example, the course of the western winds, so constant in our country, charged with the vapors of the Atlantic and heated by the Gulf-stream, over which they pass. These currents are cooled little by little by contact with the colder air which they meet, and deposit along the way part of their moisture, until, meeting the Helvetic Alps, they are still more elevated, and give out on the summit of these mountains, in the form of rain or snow, the remainder of their moisture, whence are supplied the sources of the Rhone and Rhine. It is the same with the Po, whose stream is nourished by the rains that are carried to the top of the Tyrolese Alps, these same winds blowing over the plains of Lombardy.

Let us point out in a few words the course of the trades. After having crossed the Atlantic and imbibed its vapors, these winds cross America to the Cordilleras. In crossing this colossal barrier, they are forced into the colder regions, where they are relieved of the moisture with which they are saturated, and send down the torrents of water which are soon named the Orinoco and the Amazon. Becoming dry, the trades descend to the arid plains of Peru, (where rain is unknown,) cross the wide Pacific, where they drink up new vapors, which they deposit on the mountains of Cochin China and Siam, where they become the sources of large rivers. Then, continuing their journey, they cross the Indian Ocean and carry its abundant vapors to the mountains of Central Africa, the source of the Nile, and then redescend hot and dry over the desert.

It is thus that the divine economy of the creation is brilliant in the simplicity of the cause, and in the variety and power of the effects. Even the deserts themselves play their part in the atmospheric circulation and in the irrigation of the earth : whether, being heated, one after another, by the periodic passage of the sun between the tropics they draw the trades in turn

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