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evaporates a layer of water annually 16 feet in depth. And to hoist up as high as the clouds, and lower down again, all the water in a lake 16 feet deep, and 3,000 miles broad, and 24,000 long, is the yearly business of this invisible machinery. What a powerful engine is the atmosphere !
"In some parts of the earth the precipitation is greater than the evaporation; thus, the amount of water borne down by every river that runs into the sea may be considered as the excess of the precipitation over the evaporation that takes place in the valley drained by that river. In other parts of the earth the evaporation and precipitation are exactly equal, as in those inland basins such as that in which the city of Mexico, Lake Titicaca, the Caspian Sea, etc., etc., are situated; which basins have no ocean drainage. If more rain fell in the valley of the Caspian than is evaporated from it, that sea would finally get full and overflow the whole of that great basin. If less fell than is evaporated from it again, then that sea, in the course of time, would dry up, and plants and animals would all perish there for the want of water. In the sheets of water which we find distributed over that and every other inhabitable inland basin, we see reservoirs or evaporating surfaces just sufficient for the supply of that degree of moisture which is best adapted to the wellbeing of the plants and animals that people such basins. In other parts of the earth still, we find places, as the Desert of Sahara, in which neither evaporation "nor precipitation takes place, and in which we find neither plant nor animal.
“In contemplating the system of terrestrial adaptations, these researches have taught me to regard the great deserts of the earth as the astronomer does the counterpoises to his telescope —though they be mere dead weights, they are, nevertheless, necessary to make the balance complete, the adjustments of this machine perfect. These counterpoises give ease to the motions, stability to the performance, and accuracy to the workings of the instrument. They are compensations."
A strong corroboration of the hypothesis that the southeastern trades are deflected into the upper regions of the atmosphere, is the fact that the occasional showers of dust to be met with in the Atlantic not far from the belt of calms of Cancer, and in the neighborhood of the Cape de Verd Islands, and sometimes extending to the northern coasts of the Mediterranean, contain the remains of infusoria, whose habitat is not Africa, but South America, and the southeast trade-wind region of South America. These remains cause the red fogs and sea-dust of the North Atlantic, the Cape de Verd Islands, and the dustwinds of Southwestern Europe.
THE EQUATORIAL Cloud-Ring.-The graphic essay on the above subject, by Lieut. Maury, is well known; it forms part of his theory of the circulation of the atmosphere, and the following is his explanation of its formation :
"In a clear day at the equator, this cloud-ring having slid to the north or south with the calm belt, the rays of the sun pour down upon the crust of the earth, and raise its temperature to a scorching heat. The atmosphere dances above it, and the air is seen trembling in ascending and descending columns with busy eagerness to conduct the heat off, and deliver it to the regions aloft, where it is required to give momentum to the air in its general channels of circulation. The dry season continues; the sun is vertical; and, finally, the earth becomes parched and dry; the heat accumulates faster than the air can carry it away; the plants begin to wither, and the animals to perish. Then comes the mitigating cloud-ring. The burning rays of the sun are intercepted by it. The place for the absorption and reflection, and the delivery to the atmosphere of the solar heat, is changed; it is transferred from the upper surface of the earth to the upper surface of the clouds.
“Radiation from the land and the sea below the cloud-belt is thus interrupted, and the excess of heat in the earth is delivered to the air, and by absorption carried up to the clouds, and there delivered to their vapors to prevent excess of precipitation.
"In the mean time, the trade-winds north and south are pouring into this cloud-covered receiver, as the calm and rain-belt of the equator may be called, fresh supplies in the shape of ceaseless volumes of heated air loaded to saturation with vapor, which has to rise above and get clear of the clouds before it can commence
process of cooling by radiation. In the mean time, also, the vapors which the trade-winds bring from the north and the south, expanding and growing cooler as they ascend, are being condensed on the lower side of the cloud stratum, and their latent heat is set free to check precipitation and prevent a flood.
" While this process and these operations are going on on the nether side of the cloud-ring, one not less important is going on on the upper side. There, from sunrise to supset, the rays of the sun are pouring down without intermission. Every day, and all day long, they operate with ceaseless activity upon the upper surface of the cloud stratum. When they become too powerful, and convey more heat to the cloud vapors than the cloud vapors can reflect and give off to the air above them, then, with a beautiful elasticity of character, the clouds absorb the surplus heat. They melt away, become invisible, and retain, in a latent and harmless state, until it is wanted at some other place and on some other occasion, the heat thus imparted.”
THE GEOLOGICAL AGENCY OF THE WINDS.-The geological relations between the wind, the land, and the water, are shown to have an intimate connection with the fertility and habitable quality of each region. The largest portion of the surface swept by the southeastern trades is water; but those regions which lie to the northeast of South America and Africa, in the northern hemisphere, are deserts, and were it not for the inland seas of Europe and Asia, these regions would be still more extensive. In like manner, Australia occupies in the southern hemisphere a position opposite to the continent of Asia, and, being swept by winds borne over a vast extent of land, while in contact with the surface, is found to be mostly a desert. If this contental mass were removed so as to occupy the space in the South Pacific swept by the southeast trades, which blow as southwest winds over the basins of the great rivers and lakes of North America, the channel of the Mississippi would resemble that of the Australian rivers, and present a dry and dusty trough in the midst of a desert, the great lakes would be drained, and Niagara no longer resound with the whirl of its world of waters. If ever there was a time when the Andes and the Continent of South America were submerged, then the ancient winds that fell on the region of Central Asia, and the basins of the Caspian and Aral, were swelled with the waters that now are discharged, in part, by the Amazon and Orinoco into the ocean, and those seas were united, forming a Mediterranean of vast extent, and probably discharging its waters by an estuary more magnificent than the St. Lawrence. According to the circulatory scheme of the atmosphere, the winds that play over the torrid zone of one hemisphere become the surface winds of the temperate zone of the other hemisphere. Fill up the south torrid zone, the region of the southeast trades, with land, and the north temperate zone would become one vast Sahara. Such, in brief, is the aspect of the dry season in the geological cycle, happily not co-existing with man's possession of the planet.
“ The Saltness of the Sea” is the title of another of the series of interesting papers contained in the present volume. We are unable to do more than to state that it is to this quality, in connection with the evaporation caused by heat and the passage of the winds over the water, that the currents of the ocean owe their extent and depth. By these agencies, a general circulation of the waters of the sea is maintained; and so complete is it, that the per centage of its salt is found to be nearly the same in every part of the globe.
Following the discussion of a general circulation of the waters through the entire ocean, is the argument so intimately connected with it, and now so deeply interesting both to philanthropy and science, that a permanently open sea exists in the Arctic basin. The study of the currents of the ocean have led Lieut. Maury strongly to the conclusion, that the pole is sur. rounded by this sea instead of being piled by everlasting barriers of thick-ribbed ice. The report of Lieut. De Haven, the commander of the Grinnell Expedition, the first of the noble enterprises set on foot from the United States to aid in the discovery and rescue of the lost ships of Sir John Franklin, follows; and in the midst of the dangers of the dreary cruise during the long nights of those two polar winters, a ray of hope, faint though it be, hangs over the track of the intrepid Kane, who has dared again the perils of the Arctic Sea, at the joint command of humanity and national glory.
DEEP SEA SOUNDINGS.-To determine the depth of the ocean, and approximately the outline of its abysses and shallows, will furnish data of the utmost value in completing the theory of the tides. We believe that American officers have been the foremost, and, with a few exceptions, the only investigators in this problem. Already they have contributed enough to make out à chart of the bottom of the Atlantic, which gives a general idea of the slopes and hollows of that ocean valley, and its transverse branches, the Caribbean Sea and the Gulf of Mexico. The first cruise of the “Fanny," the schooner dispatched on this service of making these explorations, cleared up all doubts as to the non-existence of certain fancied rocks and shoals which had been long enough bugbears to navigators. The following is the list of rocks found to be purely imaginary during the cruise:
71° 40' 58 40 55 50 38 20 23 45 21 15 20 45
Lieut. Berryman, in the United States brig" Dolphin,” reports, in 1853, that nothing has been found at the places indicated:
At some of these localities soundings were taken, with depths of from 2,200 to 4,600 fathoms. The greatest depth sounded in the Taney was in latitude 31° 59' north, long. 58° 43' west, on the 15th November, 1849, when 5,700 fathoms of wire were let out without reaching the bottom. The form of the deepest portion of the North Atlantic is that of a y, lying northwest and southeast,
the two divisions being in the former direction, and stretching from 20° to 40° north latitude, and from 40° to 60° west long. Just on the verge of one of the divisions of the
the Bermudas rise from the sea, forming apparently a peak mostly submerged, of nearly six miles in height. The y form is preserved in the next higher shelf of the bottom, only the tail is prolonged, forming a long trough between the two continents of South America and Africa. Two lines of soundings have recently been run across the Atlantic by Lieut. Berryman, in the Dolphin; they confirm the supposition, that the depth of the North Atlantic is nowhere greater than 5,000 fathoms. No little tical difficulty is experienced in sounding these depths, and the best check, in fact it is indispensable, to observe the rate at which the wire or twine is delivered from the reel. Without this precaution, currents and counter-currents may operate on the line long after the plummet is on the bottom. The following is a series of deep sea soundings recently made from the brig Dolphin, Lieut. O. H. Berryman, and extracted from a letter of our author. It will be seen that it exhibits the profile of two lines carried across the North Atlantic.
DEPTHS OF THE OCEAN.
Long. W. Depth in
24, 46 25,
Jan. 3, 1853
29, € 30, Feb. 3,
19 53 45. ..2,950
. 1,800 no bottom. 29 13 30......41 20 50 2,270 bottom. 31 16 00......43 28 00 2,089 33 01 00......44 31 00......
.. 2,250 32 29 00
....47 02 00 ..1,950 no bottom. 32 55 00......47 58 00......
..6,600 doubtful. 33 03 00 48 36 00......3,550 bottom. 32 47 00 .....50 00 00.... .3,240 no bottom. 28 59 00. 57 51 00...
.1,380 bottom. 28 20 00 59 44 00 ....2,900 doubtful. 28 04 00.
61 44 00 .3,000 bottom. 28 23 00. 64 17 00 ..2,518
66 11 15 . 1,000 no bottom.
66 54 00. ..2,720 bottom. 28 16 00......69 24 00. . 2,950
11, 12, 13, 15,
27 42 36...