Malta, and other places. Now the celebrated naturalist of Berlin, Ehrenberg, provided with his powerful microscope that wonderful instrument that reveals the boundaries of the infinitesimal world, as the telescope of Lord Ross reveals those of the universe has discovered in the matter that composes these dust showers the débris of infusoria and of organic matter brought from South America, and which could only reach Europe by traversing the regions of calms. When, in his distant journeys to the torrid zones, Alexander Humboldt observed the formation of whirlwinds of dust, of which he speaks, the illustrious savant did not suppose that this dust, carried by the winds above the equatorial and tropical calms, would fall in showers upon the European shores, and carry there the proof of the upper currents of the atmosphere.

These facts, and many others that want of space will not permit us to notice here, suggested to Maury his theory of winds, a theory subtle as it is ingenious, and of which we will endeavor to convey an idea.

Above the regions where the four zones of surface winds extend, according to the sagacious meteorologist, four higher and parallel counter-currents blow opposite to the first, charged with re-establishing continually the equilibrium of the atmosphere. The intermediate calms are produced, at the equator by the meeting of the trades; at the tropics by that of the superior opposing winds. The expression "calms" is relative, the atmospheric ocean having, no more than the other ocean, absolute repose; this word only signifies the cessation of the horizontal motion of the air and the commencement of its double vertical movement, ascending in the regions of equatorial and polar calms, and descending in the tropical zones; a movement which the barometer points out here by its elevation, there by its depression.

If we follow, in thought, a particle of air in its restless voyage around the globe, we shall see it carried in turn, by the superior currents and the surface winds, to feed alternately the trades of the south and the free winds of the north in going, and the trades of the north and the free winds of the south in returning. All the intermediate places will be overleaped by it in the higher currents. What force determines these currents and drives them thus in opposite directions? What

power prevents the dry and moist air from commingling in the zones of calm, and sends the first to the equatorial seas, from which it will soon imbibe moisture, and the second to the colder regions, where it carries the rain with which it is surcharged, without ever the confusion of the two disturbing the harmony of this marvelous circulation? Maury supposes that in these phenomena are concerned the influences of electromagnetism, that mysterious and powerful agent so universally present and as yet so little known.

The rotation of the earth's crust around its central mass, which is in a state of fusion, and whose revolutions are less rapid, produces, according to M. Babinet, a double current of electricity, negative in the liquid, and positive in the solid matter. This rotatory motion being greatly accelerated at the equator, the electricity is formed there in much greater abundance. The atmospheric currents, taking up the positive, (positive electricity being in excess,) carry it to the poles, where it is accumulated, and where, meeting with the negative electricity, it produces the magnificent electrical storms which are called Auroras-the intermittent sun of those desolate regions where the sun does not shine. It is to this same polar electricity that Maury attributes the whirl of atmospheric currents around the poles. Faraday has recently demonstrated the magnetic properties of oxygen, a gas that composes the fifth part of the air we breathe. Do not these properties assist in the circulation of the atmosphere? The positions assigned to the magnetic poles-the pole of the winds and that of greatest cold-are nearly identical. Can this be pure coincidence? What force, unless it be electricity, draws on the hurricane and makes it whirl in the same manner that the spiral of the polar current does, to which it is nearly related, that is to say, from right to left in the northern hemisphere, and from left to right in the southern ?*

*The Newtonian gravitation is, perhaps, only a phenomenon of the same kind. The law of universal attraction was only to Newton himself but the rule of a fact and not of a cause; bodies are not attracted in truth, but pass from one to the other as if they were attracted. The effect only is constant, the cause is unknown. The dynamic power of the solar heat would be, according to some savans, more than sufficient to determine the rotatory motion of the planets. For what is this solar heat itself except an electrical phenomenon, according to the most generally received opinion? It is true there are those who assign as a cause for it the im

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 we 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 surface 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.

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