tains, condensed by the cold, fall in the form of rain. The proportional cooling of the air is about 37° 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

The air saturated with watery vapor and that in which this moisture is absent, 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.

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.

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

and

to the north and south of the line, according to the seasons, cause the monsoons to blow in two directions during six months alternately, as do the broiling deserts of Africa and Asia; or whether, in cooling the air, they cause an abundant precipitation, as do the icy steppes of Siberia, from whence the rain nourishes the sources of the Obi, Lena, and Yenesei.

Mountains, deserts, waters, and winds all join in the universal harmony. All, if we may be allowed the expression, perform their part in the great concert of nature.

When the winds have to pass over large continents that deprive them of their moisture, Providence, by wonderful wisdom, has placed along their route lakes and interior seas to refresh them and fill them with vapors, with which they irrigate, in proportion as they receive moisture, the countries over which they pass. Thus the trades of the south, after having traversed South America, on the heights of which they have left their moisture, descend from the higher regions in leaving the calms of the Tropic of Cancer and arrive changed in our hemisphere, where they blow from southwest to northeast, as prevailing winds, passing on their way the Mediterranean, Black, Caspian, and Aral Seas. It is the same with the trades that have crossed the south of Africa, which fall hot and dry on the Egyptian land, and then pass on to drink up the vapors of the Red Sea and the Persian Gulf. Such is the avidity of these winds that the first absorbs from the Mediterranean three times the quantity of water that this sea receives from the rivers and the rains, and the second takes up from the Red Sea a stratum of water not less than eight feet in thickness. The Straits of Gibraltar and Bab-el-Mandeb are constantly reestablishing the level of these two seas and repairing their losses.

If we believe Maury, the winds are not only the irrigators of the earth; they are also its historians, the chronographers of its changes. Why, for instance, is the Dead Sea twelve hundred feet below the level of the Mediterranean? Why are the waters of the great Salt Lake of Utah, Lake Tadjurra, and those of Titicaca, in America, progressively becoming lower? Why did the great chain of North American Lakes, which now empty their surplus water into the ocean only through the St. Lawrence, formerly empty it into the Mississippi by channels of which there are still evident traces? To all these effects

Maury assigns one cause: At an unknown epoch, yet comparatively recent, as geology makes evident, the South American continent emerged from the bosom of the waters, and elevated the immense chain of mountains which are called the back-bone of the two Americas. Previous to this period the winds, filled with the vapors of the Atlantic and Pacific Oceans, then but one sea, carried the rains to North America and Europe, and kept up the level of the interior seas. These same winds, whose direction has not changed, it being determined by the rotation of the earth, had afterward to elevate themselves over the land and mountains, which, depriving them of the most of their moisture, left them none to distribute, and it is owing to this geological phenomenon that rain is scarce in the basins of the two continents which they are charged to supply.

Thus, according to Maury, is explained the progressive falling of the waters of the interior seas; an action that continues until precipitation and evaporation become equal. The same thing would happen to the Mediterranean and Gulf of Mexico if the straits that unite them to the Atlantic should become closed; these two seas, as we have before seen, losing more by evaporation than they gain by rivers and rain. It is proper to remark, that the movement by which the Rocky Mountains, and with them the western coast of North America, have been elevated, still continues;* on the other hand, the eastern coasts are lowering by a slight depresssion.

It is to this double phenomenon that M. Elisha Reclus, in a recent and very interesting work on the Mississippi, attributes the force that draws this river toward the east, although the motion of the earth generally gives an opposite direction to the movable particles on the surface.

It is thus that geology and meteorology join hands and assist in the solution of their respective problems. It is thus that, in this beautiful theory, all is held together by a powerful logic, and facts come in crowds to the support of the opinions of a genius as sagacious as bold.

Here we must mention a remarkable occurrence that, a few years ago, demonstrated the practical advantage of meteorological science.

*This is also true of Scandinavia and the western coasts of France, where the progressive elevation is perceptible.

The reader doubtless recollects the terrible hurricane of the 14th November, 1854, which disturbed the Black Sea and ravaged the Crimea, sowing in its passage shipwrecks and devastation. Meteorology has given to this storm an explanation, if not completely irrefutable, at least very plausible. All the wise men of the civilized world having been questioned by M. Leverrier as to the atmospheric changes which preceded, accompanied, and followed the phenomenon, M. Lias, of the Observatory, was charged with arranging the reports that were transmitted. On examination, it was evident that on the 12th of November, at midday, (Paris time,) the barometers in all the western countries of Europe noted the pressure of a vast stratum of air that was elevated on the surface of the atmospheric ocean like an immense wave, stretching from north to south and advancing slightly toward the east. Hour by hour the barometers marked the march of this gigantic billow of air from west to east, which caused everywhere a remarkable calm, precursor of the tempest. It was preceded and followed by an empty furrow, equally extended as itself, and indicated by the barometer. The furrow that it preceded arrived on the 14th of November on the shores of the Black Sea. If an ordinary depression of atmosphere produces the rains and the winds, and often the tempest, what might not follow this immense furrow? We know of its fearful ravages. The wreck of the "Henri Quatre," stranded on the coast of Crimea, is still a witness of its fury. By a striking coincidence, on the 14th of November the eastern furrow devastated the Crimea, and on the 15th and 16th the western rioted in the whirlwind over France and the neighboring countries. May we not think that the destructive effect of this tempest might have been, if not shunned, at least lessened, if the observations had preceded and not followed, to be explained after the blow?

If we suppose posts of observation scattered over the globe, and communicating instantly to each other by means of electricity their remarks on the direction of the winds, the course of the clouds charged with moisture, the currents of cold or hot air, in a word, all the different atmospheric changes, what a view would thenceforth be opened toward the practical advantage of meteorology!