XIV. ESPY'S CONCLUSIONS IN METEOROLOGY.

Mr. Espy's first report on meteorology, made to Congress at its last session, contains quite a copious collection of facts to illustrate the natural history of storms in the United States. The following are the conconclusions, or "generalizations," which he has formed from them. As it is desirable to draw the attention of meteorologists to the subject, in order that these conclusions may be verified or disproved by a series of observations in all parts of the country, we lay them before our readers :

"1st. The rain and snow storms, and even the moderate rains and snows, travel from the west towards the east in the United States, during the months of January, February, and March, which are the only months yet investigated.

"2d. The storms are accompanied with a depression of the barometer near the central line of the storm.

"3d. This central line of minimum pressure is generally of great length from north to south, and moves, side-foremost, towards the east. "4th. This line is sometimes nearly straight, but generally curved, and most frequently with its convex side towards the east.

"5th. The velocity of this line is such, that it travels from the Mississippi to the Connecticut River in about twenty four hours, and from the Connecticut to St. John, Newfoundland, in nearly the same time, or about thirty-six miles an hour.

"6th. When the barometer falls suddenly in the western part of New England, it rises at the same time in the valley of the Mississippi, and also at St. John, Newfoundland.

"7th. In great storms, the wind, for several hundred miles on both sides of the line of minimum pressure, blows towards that line directly or obliquely.

"8th. The force of the wind is in proportion to the suddenness and greatness of the barometric depression.

"9th. In all great and sudden depressions of the barometer, there is much rain or snow; and in all sudden great rains or snows, there is a great fluctuation of the barometer.

"10th. Many storms are of great and unknown length from the north to the south, reaching beyond our observers on the Gulf of Mexico, and on the northern lakes, while their east and west diameter is comparatively small. The storms, therefore, move side-foremost.

11th. Most storms commence in the Far West,' beyond our most western observers, but some commence in the United States.

"12th. When a storm commences in the United States, the line of minimum pressure does not come from the ' Far West,' but commences with the storm, and travels with it towards the east.

"13th. There is generally a lull of wind at the line of minimum pressure, and sometimes a calm.

"14th. When the wind changes to the west, the barometer generally begins to rise.

“15th. There is generally but little wind near the line of maximum pressure, and on each side of that line the winds are irregular, but tend outwards from that line.

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16th. The fluctuations of the barometer are generally greater in the northern than in the southern parts of the United States.

"17th. The fluctuations of the barometer are generally greater in the eastern than in the western parts of the United States.

"18th. In the northern parts of the United States, the wind, in great storms, generally sets in from the north of east, and terminates from the north of west.

"19th. In the southern parts of the United States, the wind generally sets in from the south of east, and terminates from the south of west. "20th. During the passage of storms, the wind generally changes from the eastward to the westward by the south, especially in the southern parts of the United States.

XV. THE INFLUENCE OF AGRICULTURE ON CLIMATE IN LESSENING STREAMS, ETC.

[From the "Rural Economy" of J. B. Boussingault.]

A question of great importance, and that is frequently agitated at this time, is, as to whether the agricultural labors of man are influential in modifying the climate of a country or not? Do extensive clearings of woods, the draining and drying up of great swamps, which certainly influence the distribution of heat during the different seasons of the year, also exert an influence on the quantity of running water of a country, whether by lessening the quantity of rain which falls, or by promoting the more speedy evaporation of that which has fallen ?

In some districts it has been held, that the streams which had been used as moving powers, have very sensibly diminished. In other places, the rivers are said to have shrunk visibly; and in others, springs that were formerly abundant, have almost dried up. Observations to this effect appear to have been principally made in valleys, surmounted by mountains; and it is generally asserted, that the falling off in the springs and streams had followed close upon the period at which the woods, scattered over the surface of the country, were cleared away without any kind of reserve.

The lakes which are met with in plains, and at different levels in mountain ranges, seem to me peculiarly calculated to throw light on this subject. Lakes may, in fact, be received as natural gauges of the run

ning waters of a country. If the mass of the water contained in the lakes undergo change in one direction or another, it is obvious that this change, and the direction in which it has occurred, will be proclaimed by the state or mean level of the lake or lakes, which will differ for the same reason that it does at different seasons of the year, viz. as drought or rain prevails. The mean level of the lake or lakes of a district will, therefore, fall, if the quantity of water which flows through that district diminishes; the level, on the contrary, will rise, if its streams increase; and it will remain stationary if the afflux and efflux of the lake continue unchanged. In the following remarks, I shall attach myself particularly to observations upon lakes which have no outlet, by reason of the facility with which any, even slight, change in the level of these must be discovered. I shall not, however, neglect those lakes which have an exit by a stream or canal, because I believe that the study of these may also lead to accurate enough results; the only point requiring preliminary remark is the sense in which the words, change of level, are to be taken.

One of the most interesting portions of Venezuela is, undoubtedly, the valley d'Aragua. Situated at a short distance from the seaboard, possessed of a warm climate, and of a soil fertile beyond example, it combines within itself all the varieties of agriculture that belong in peculiar to tropical regions; on the hillocks, which rise in the bottom of the valley are seen fields which bring to mind the agriculture of Europe. Wheat succeeds pretty well upon the heights which surround La Vittoria. Bounded on the north by a chain of hills, which run parallel with the sea-board, and to the south by the range which separates it from Llanos, the Aragua Valley is limited on the east and west by a series of lesser elevations, which shut it in completely. In consequence of this peculiar configuration of country, the rivers which rise in its interior have no outlet to the ocean; their waters accumulate in the lowest part of the valley, and form the beautiful lake Valentia. This lake, which M. de Humboldt says exceeds the lake Neufchâtel in size, is raised about 1300 feet above the level of the sea; it is about ten leagues in length, and about two leagues and a half where it is widest.

At the time when M. de Humboldt visited the Aragua Valley, the inhabitants were struck with the gradual diminution which had been going on in the waters of the lake during the last thirty years. It was enough to compare the statements of older writers with its condition at this time, to obtain conviction that the waters had, in fact, very much diminished. Oviedo, for instance, who visited the valley frequently towards the end of the sixteenth century, says, that the town of New Valencia was founded in 1555, at a distance of half a league from the lake; in 1800, M. de Humboldt ascertained that the lake was upwards of 4549 yards, or upwards of 34 miles, instead of about 114 mile from its banks.

The appearance of the surface also gives new proof of the fact of the

recession of the water; certain hillocks which rise in the plain still preserve the title of islands, which, undoubtedly, they formerly received with propriety, when they were surrounded by water. 'The land which had been left by the retreat of the lake, soon became transformed into beautiful plantations of cotton-trees, bananas, and sugar-canes. Buildings, which had been erected on the banks, were left, year after year, further and further from them. In 1796, new islets made their appearance. An important military position, a fortress built in 1740, in the Isle de la Cabrera, was then upon a peninsula. Finally, in two islets of granite, M. de Humboldt discovered, several yards above the level of the lake, a bed of fine sand mixed with fresh water shells. These facts, so certain, so unquestionable, did not pass without numerous explanations from the wise men of the country, who, as if by common consent, fixed upon a subterranean exit for the waters of the lake. M. de Humboldt, after the most careful examination of all the circumstances, did not hesitate to ascribe the diminution of the waters of the lake Valencia, to the extensive clearings which had been effected in the course of half a century in the Aragua Valley. "In felling the trees which covered the crowns and slopes of the mountains," says this celebrated traveller, “men in all climates seem to be bringing upon future generations two calamities at once-a want of fuel and a scarcity of water."*

In the year 1800, the population of this favored valley, where the cultivation of indigo, of cotton, of cocoa, and the cane, had made immense progress, was as dense as it was in the most thickly populated districts of England or France, and every one was delighted with the appearance of comfort that prevailed in the numerous villages of this industrious country.

Twenty-five years after M. de Humboldt, I explored in my turn the valley d'Aragua, having fixed my residence in the little town of Maracaibo. The inhabitants had now remarked, that for several years, not only had the lake ceased to diminish, but that it had even risen very perceptibly. Some fields that were formerly covered with cotton plantations were now submerged. The Isles de las Nuevas Aparacidas, which had risen from the waters in 1796, had again become shoals dangerous to navigation; the tongue of earth de la Cabrera, on the north side of the valley, had become so narrow that the slightest rise in the water of the lake covered it completely; a continuous N. E. wind was sufficient to flood the road which led from Maracaibo to New Valencia; in short, the fears which the inhabitants of the lake had entertained for so long a period had entirely changed their nature; they were now no longer afraid of the lake drying up; they saw with dismay that, if the water continued to rise as it had done lately, it would, in no long space of time, have

* Humboldt, vol. v. p. 173.

drowned some of the most valuable estates, &c. Those who had explained the diminution of the lake by supposing subterraneous canals, now hastened to close them up in order to find a cause for the rise in the level of the water.

In the course of the last twenty-two years important political events had transpired. Venezuela no longer belonged to Spain; the peaceful valley d'Aragua had been the theatre of many a bloody contest; war to the knife had desolated this beautiful country and decimated its inhabitants. On the first cry of independence raised, a great number of slaves found freedom by enlisting under the banners of the new republic; agricultural operations of any extent were abandoned, and the forest, which makes such rapid progress in the tropics, had soon regained possession of the surface which man had won from it by something like a century of sustained and painful toil. With the increasing prosperity of the valley, many of the principal tributaries to the lake had been turned aside to serve as means of irrigation, so that the beds of some of the rivers were absolutely dry for more than six months in the year. At the period which I now refer to, the water was no longer used in this way, and the beds of the rivers were full. Thus with the growth of agricultural industry in the Valley d'Aragua, when the extent of cleared surface was continually on the increase, and when great farming establishments were multiplied, the level of the water sunk; but by and by, during a period of disasters, happily passing in their nature, the process of clearing is arrested, the lands formerly won from the forest are in part restored to it, and then the waters first cease to fall in their level, and by and by show an unequivocal disposition to rise.

I shall now, without however quitting America, carry my readers into a district where the climate is analogous to that of Europe, where the surface is occupied by immense fields, covered with the cereals, as with us. I speak of the table lands of New Granada, of those valleys raised from 10,000 to 13,000 and 14,000 feet above the level of the sea, in which the mean temperature throughout the year ranges from 58° to about 62° Fahr. Lakes are frequent in the Cordilleras; and it would be easy for me to describe a great number; I shall, however, confine myself to those which became subjects of observation in former times.

The village of Ubaté is now situated in the neighborhood of two lakes. Some seventy years ago these two lakes formed but one; the old inhabitants saw the water shrinking and new fields presenting themselves year after year. At this present time fields of wheat of extraordinary luxuriance occupy levels that were completely inundated 30 years ago.

It is enough, indeed, to perambulate the neighborhood of Ubaté, to consult the old sportsmen of the country, and to refer to the annals of the various parishes, to be satisfied that extensive forests have been cut down in the whole of the surrounding country; the clearing, in fact, still con