The drift-current is, in some measure, observable all over that portion of the Atlantic Ocean which is under the influence of the trade-winds; but as these winds are not very constant to the north of the 23d parallel, and rarely extend to the south of the 9th, the current is constant only between these two boundaries. In the region of the calms it is very weak, and often entirely ceases. But in those regions in which the southern trade-winds blow, it is again perceptible and constant, except along the coasts of Africa, where it has rather a northerly than a westerly motion; the latter, however, becomes by degrees more prevalent in proportion as the wind takes that direction in advancing to the west. The mean velocity of this current is from 9 to 10 miles per day, or, according to the computation of Humboldt, only one-fourth of the velocity with which those rivers in Europe commonly flow on which observations have been made. The drift-current, which in the northern portion of the Atlantic is produced by the prevalent westerly winds, flows in a westerly direction; but it is not perpetual, and is so slow, that, when a ship keeps clear of the Gulf Stream, it only manifests itself generally on the whole course of a voyage from Europe to America and vice versa, retarding the former and forwarding the latter. besides the tides, two kinds of motion are to be distinguished | both sides of the equator, as far as 22° W. long., where it in the sea, which we shall name with Major Rennell the sends off a branch to the north-west. Soon afterwards it drift-currents and the stream-currents. declines somewhat to the south, and runs in this direction The drift-currents owe their origin to the effects produced towards the two capes of St. Augustin and St. Roque, on on the surface of the sea by the perpetual or prevailing the Brazilian coast. At the distance of about 300 sea-miles winds; the former, even where they do not blow with great from these capes, it divides into two currents; the northern, force, by their uninterrupted continuance displace and push running along the shores of Guiana, and hence deriving forward the upper strata of the water, and thus produce a the name of Guiana Current, enters the Caribbean Sea motion towards the region to which they blow. These by the straits which separate the Leeward Islands, lying drift-currents are constant, and run always in the same to the south of Martinique, from each other and from direction and commonly with pretty equal velocity. The the continent of South America; and in some measure drift-currents produced by the prevalent winds are not so in this sea it may be supposed to terminate its course. constant and do not always run in the same direction nor The Brazil Current, or the other branch of the equatorial with the same velocity. In the Atlantic Ocean, the former current, runs to the south-west along the shores of Brazil, kind of drift-current is found only between the tropics, to the mouth of the Plata River, and may even be traced where it is produced by the trade-wind; and the latter to to the Straits of Magalhaens and of Le Maire. The the north and south of 30°, where they are ascribed to the whole length of this current, from St. Thomas to Cape effects of the prevalent winds. St. Roque, amounts to upwards of 2500 nautical miles; and if we add the Guiana current, from the point of division opposite that cape to the strait dividing the island of Trinidad from that of Grenada, its course is increased by 1500 nautical miles more. The breadth of the current is different in different parts. Near the islands of St. Thomas and Anno Bom, it extends not quite over three degrees of latitude, occupying about 160 miles. But, in proportion as it advances to the west, it increases in breadth; opposite Cape Palmas it extends from 1° 45' N. lat. to near 5° S. lat., thus occupying in breadth more than six degrees, or upwards of 360 nautical miles. Farther to the west it enlarges still more, and attains its greatest breadth, extending over 7° or 8° of lat. from 44° or 5° south of the equator to 24 or 3° north of it. Here, therefore, the breadth of the current occupies 450 geographical miles, or not much less than the whole length of Great Britain, from the Lizard to Cape Wrath. But having soon afterwards, between 22° and 23° W. long., sent off a branch to the north-west, it narrows to about 300 nautical miles; and this breadth it probably preserves to the point where it divides opposite the capes of St. Augustin and St. Roque. The velocity of the current is different in different parts, and increases or decreases according to the seasons, it being much greater in summer than in winter. From Anno Bom to 10° W. long. it runs, at an average, from 25 to 30 miles per day; but from 10° to 16° W. long. it is much more rapid-making, in the same time, from 44 to 79 miles at the end of June and the beginning of July. This seems to be the strongest part of the whole stream: But it is only in the months of May, June, July, and August, that it runs with great force; from October to March it is moderate, and sometimes very weak. Between 16° and 23° W. long. lies the common track of the vessels; and here the rapidity of the current rises often to 45, 50, and even 60 miles per day, but its mean velocity may be estimated at about 28 nautical miles; it is strongest near the equator, and stronger to the north than to the south of it. From 23° to the coasts of Brazil, the current becomes rather stronger, and seems to be less affected by the seasons; but its velocity in these parts is not exactly ascertained; it seems, however, to run 30 miles and upwards per day. The temperature of the water in the current varies also, according to the seasons and the different parts of its course, but it is always some degrees lower than that of the ocean. The water of the ocean to the north of the current is 80° or 81° Fahrenheit, and to the south, 78° or 79° in summer; but in the current, the thermometer shows, near Anno Bom and St. Thomas, only 75°, and not more to a great distance westwards, where the temperature falls even to 73, and at this temperature it remains for more than 12° of longitude. Afterwards it rises again to 74°, and by degrees to 76° Fahr. In summer the temperature of the current may be estimated as being, at an average, 5° or 6° under that of the water of the ocean; but in winter it is much less. This current greatly affects the course of vessels which are obliged to cross it, and creates great delays to those who, passing from the north to the south, traverse the equator west of the 23° of long., carrying them forcibly to the west beyond Cape St. Roque, where they are driven towards the northern shores of Brazil, and are not able to regain their course till after weeks, and even months, of toilsome labour. It is a fortunate circumstance that the direction of this current does not coincide with the region of the calms; otherwise, both together would probably form an impenetrable barrier to the progress of vessels navigating these seas. But the southern trade-wind commonly blows in that region It is easy to conceive that the drift-currents, especially the permanent, are very favourable to navigation, by rendering the voyages to some countries more easy, more certain, and less dangerous. But the stream-currents are much less so. Up to the present time they have commonly proved adverse, causing great loss of life and property, and forcing vessels out of their course. Many navigators, running from Madeira to Teneriffe, and expecting to arrive at the latter island, have unexpectedly found their vessels cast upon the shores of Africa, nearly 300 sea miles out of their course. Such errors can only be detected by frequent astronomical observations, and by comparing them with the dead reckoning. If they are not detected in time, shipwrecks sometimes become unavoidable. We cannot compare the stream-currents of the ocean with the rivers of the continents. The stream-currents cover such a portion of the surface of the sea, that were they transferred to the continents, they would no longer be considered as rivers, but as large branches of the sea. The causes to which they owe their origin are still involved in obscurity; our observations have not yet penetrated into the depth of the sea, they have only slightly investigated its surface, and there are some facts which lead to the opinion that the stream-currents are of great depth, and in many parts, if not in all, extend to the bottom of the sea. This indicates clearly that their origin must not be ascribed to changes which take place on its surface, and cannot affect the lower strata of its waters. The opinions which have been formed on this object may be seen under the article CURRENTS. We shall here only notice the largest of the current streams which belong to the Atlantic Ocean, and indicate their extent, velocity, and temperature, their only properties which, up to this time, have been in some degree ascertained. Two large stream-currents traverse the Atlantic Ocean; the Equatorial Current, running from the coast of Africa to that of South America, and the Gulf Stream, flowing from North America to the shores of Europe. The Equatorial Current, so called from its course lying under or near the Line, may be supposed to be formed between the islands of St. Thomas and Anno Bom, in the bight or bay of Benin. Hence it proceeds to the west on where the equatorial current runs, at least during those | known of the Atlantic currents, is the Gulf Stream, whicn months in which it runs with great force. traverses the sea between the parallels of 36° and 44° in the That branch of the equatorial current which separates northern hemisphere. Its origin is in the Gulf of Mexico, from it between 22° and 23° W. long., and at about 2 N. where the warm water which enters it from the Caribbean lat., is rather favourable to navigation, by forwarding the Sea, between Cape Catoche and Cape St. Antonio, by being course of vessels returning from the southern hemisphere. subjected to a nearly circular rotation, and influenced proIts course lying in a north-western direction, it may be bably by other causes still unknown, is raised to a high decalled the North-west Current. Its breadth is consider-gree of temperature, the thermometer indicating 86°, while able, and may be estimated, at the point of separation, at under the same parallel (25° N. lat.) the ocean only shows 78°. 180 or 200 miles; farther northward, even at 300; and at a Two currents, which put in motion perhaps three-fourths of more considerable distance, at 240 nautical miles; but its the waters of the Gulf of Mexico, unite about 60 nautical velocity is not so great as that of the main equatorial current. miles to the westward of Havannah, between the bank of Up to 10° N. lat., however, and even a little farther, it may Isabella on the side of Cuba, and the Tortugas on that of run from 20 to 24 miles per day; but it then slackens, and Florida Reefs; and this union gives rise to the Gulf Stream. becomes less perceptible, though it may at all times be In the beginning its course is not rapid, and along the traced to 18° N. lat., and commonly even to 25°. In the shores of Cuba it is weak, and sometimes nearly imperatter part it bends more to the northward, and at last is ceptible: but it soon increases in velocity, and before it lost in the drift-current, to which it seems to give a north-enters the Strait of Florida at the Salt Kays, it runs one westerly direction, which is observable all the way from mile and a half per hour on an average; in the strait itself 35° W. long. to Trinidad. The accelerated motion of the it acquires a formidable swiftness. The Strait of Florida drift-current in these seas may also, in some measure, be begins at the Salt Kays, a reef lying 114 nautical miles to the effect of this north-west current. the north-east of Havannah, and extends thence to the northward, where it terminates between the reefs of Cape Cañaveral and the northern termination of the Lesser Bahama Bank, at about 28° N. lat. After entering this strait, the velocity of the Gulf Stream soon increases to 24, 3, and occasionally 4 miles per hour; but after running at this rate about 90 miles, it arrives at the Narrows, where, between Cape Florida and the Bimini Islands (a small group belonging to the larger group of the Bahamas), the strait is only 44 miles wide, and its water-way, by reefs and shoals, is straitened to 35 miles. Here the current runs, in the month of August, at 5 miles per hour, and seldom below 5 through the remainder of the strait, which towards its northern extremity widens to about 50 miles. In this course the current has traversed about four degrees of lat. northward, but its temperature is not sensibly diminished. The Guiana Current is, properly speaking, the continuation of the equatorial current, and runs from Cape St. Roque in Brazil, to the Island of Trinidad, along the low coast of Guiana, and at no great distance from it. It is of considerable breadth, and of great velocity, running at some places two miles per hour. Here too it is observed that its velocity is much greater in summer than in winter and spring; and it is besides much increased by the waters rushing from the mouth of the Amazon river into the sea; for after this has taken place, the current runs three miles per hour. It is, however, to be observed, that the waters of the Amazon river do not mingle with those of the current: they cut them at right angles, and running with great violence, cause eddies and whirlpools; but at last the river passes the current, and is observable at a distance of 500 miles from its mouth. It is remarkable that the Amazon causes no change in the direction of the current. Farther to the north, the Orinoco enters the current. This river, which pours a prodigious mass of water into the ocean on both sides of the island of Trinidad, enters the current at a very acute angle; and thus soon mixes its water with it, and consider-siderably in breadth, and decreases in velocity and temperaably accelerates its course. Soon afterwards the current enters the Caribbean Sea by the straits lying between Trinidad and the island of Martinique. Between Trinidad and Grenada, it runs from 1 to 1 mile per hour; less between St. Vincent and St. Lucia; and between the latter island and Martinique its course is reduced to 21 miles per day. Farther to the north, and especially at the Virgin Island, the sea-water runs only from 8 to 10 miles per day, and that is the common rate of the drift-current. We find no observations whether the water of this current differs in temperature from that of the ocean. It may be said that the Guiana current is lost in the Caribbean Sea, for in the latter no perpetual current has been observed. The whole course of the Guiana current may be reckoned at about 2500 nautical miles. The third branch of the equatorial current is the Brazil Current, which branches off from the equatorial at 8° S. lat., opposite Cape St. Augustin, at a distance of about 300 miles to the east of it. Between the point where it branches off and 16 or 17° of S. lat. it has considerable breadth, and does not approach the shores of South America nearer than 250 miles. Afterwards it increases in breadth and velocity, and approaches nearer the land. Opposite Cape Trio it is 200 miles from the coast, and runs about 30 miles per day. As the shore south of this cape falls off to the west, the current is at a greater distance; and though it soon changes its direction, it does not approach nearer than 250 miles to the coast, off the mouth of the Plata river, running all this way from 15 to 20 miles per day. It is crossed by the Plata river, just as the Guiana current by the Amazon river. Here too the current of the river is observable in the sea at a distance of upwards of 500 miles, but it seems not to have the least effect in changing the direction of the streamcurrent, which continues, though much weakened, farther to the south, and may be traced to the Straits of Magalhaens and Le Maire. As this current runs at a considerable distance from the shores of Brazil, the intermediate space is occupied by other currents, which mostly, however, follow the direction of the monsoons which blow along this coast. The most remarkable, and at the same time the best Issuing from the Strait of Florida, the Gulf Stream runs northward along the shores of Florida to 31° N. lat., and afterwards nearly north-east along the shores of Georgia and of both Carolinas, as far as Cape Hatteras (about 35° N. lat.). In this course the current widens conture. Opposite the harbour of Charlestown, its breadth is from sixty to sixty-three miles; and at Cape Hatteras, from seventy-two to seventy-five miles. At the latter place it runs only three and a quarter miles per hour, or seventyeight miles per day, and its temperature has fallen from 86 to 83°. At Cape Hatteras, the north-western or inner edge of the current is twenty-four miles south-east of the cape. By the falling back of the coast north of Cape Hatteras, the current directs its western edge towards the north, while the main body continues its former course to the north-east to a considerable distance. At about 40° N. lat. it meets the extensive Nantucket and St. George's Banks, which turn it off seaward, and it never after approaches the land. From this point it runs in the direction E. N., brushing the southern extremity of the Great Bank of Newfoundland, and it continues in this line to 43° and 44° long., and 37° and 43° lat. Here, however, it bends by degrees to the east, south-east, and south, and having enclosed the islands of Flores and Corvo, which belong to the group of the Azores, its traces are lost in the water of the ocean. Sometimes, though rarely, the warm water of the current has extended to the shores of Europe. In this part of its course across the ocean, it is very difficult to ascertain the breadth of the current, because the warm water expands to the north and to the south to a considerable distance in the sea, where no current can be traced; in the former direction to a degree, or a degree and a half of latitude; and on the southern side, even to two degrees and a half it has been met with at 3330 and 34° lat. The strongest current is commonly met with between 38° and 39° lat.; and it is the opinion of many intelligent navigators, that the breadth of what may be called a current does not exceed 100, or 120 nautical miles. The warm water sometimes only extends to 140 miles, and then it seems to occupy only the cur rent, but at other times it is found to cover 186, 240, 270, and even 320 miles. It does not seem that this difference in the extent of the warm water is affected by the seasons, for both extremes have been found to exist in the same month (May), between 63° and 65° long. It is very probable that the main current does not always run in the same places, but is subject to some changes in its position, though probably not much in its direction. Its velocity decreases gradually in its progress to the east. Between the meridians of 65° and 66° it runs between fifty-five and fifty-six miles per day; and 900 nautical miles farther to the east, from thirty to thirty-three miles. After it begins to bend to the east and south-east, its velocity diminishes more rapidly; in the neighbourhood of the Azores, its mean rate does not exceed ten miles per day, having lost twenty miles per day in a course of only 600 miles. The temperature of its water likewise decreases during all this course, but at a slower rate. For, 600 nautical miles from Cape Hatteras, or under the meridian of 6340, the thermometer shows 81° in summer, or from 104° to 1130 above the water of the ocean under the parallel, after having traversed 4° of lat. Hence, to 4240 lat. and 430 long., it loses 54° of heat, the thermometer falling | from 81° to 7540. Thence to Corvo, the thermometer descends from 75° to 724°, still preserving a temperature 8°, or 10° above that of the ocean. through stormy latitudes; whilst it is only necessary to navigate one-third of it when another course is chosen, and therefore vessels returning from the West Indies have resumed the old road, used before the discovery of the Gulf Stream, south of the Bermudas to Corvo. Besides the Gulf Stream, two other currents in the North Atlantic deserve notice, the Arctic Current and the North African or Guinea Current. The Arctic Current, which seems to originate in the extensive masses of ice which surround the North Pole, runs down along the eastern shores of Greenland, whence it carries numerous ice-fields to the south-westward. These masses, along the coast of Greenland, are found extending from 250 to 300 miles from the shore into the open sea, and mark, as it were, the breadth of the current, which fills with them the strait that divides Iceland from Greenland, and carries them to Cape Farewell the most southern extremity of Greenland. It then turns round the Cape and runs up the western coast of Greenland; but it seems that it afterwards crosses obliquely Davis's Strait, and is turned to the southward by Cape Walsingham (about 66° N. lat.). For, from this Cape a current of eight or nine miles per day runs to the southward, which at the mouths of the straits of Cumberland and Hudson increases in velocity to fifteen or sixteen miles per day. It follows the coast of Labrador until it arrives at the strait of Belle Isle, separating Newfoundland from the continent of America, where it divides, sending a branch through the strait, which afterwards joins the outfall of the St. Lawrence river, while the main body of the current The whole course of the Gulf Stream, from the Salt Kays running to the east of Newfoundland passes between the to the south-west of the Azores, amounts to upwards of Great and the Outer Bank of Newfoundland, or between 3000 nautical miles, in which course it traverses from 19° 45° and 46° lat. and 46° and 47° long., and at last joins the to 20° of lat. (23° to 42°, or 43°), and diminishes in tem- Gulf Stream between 43° and 47° of long. The breadth of perature 134° (from 86° to 7210). According to Major Ren- the current in this part probably does not exceed 200 or 240 nell, it arrives at the Azores in seventy-seven or seventy-miles, but its temperature is always below that of the ocean, eight days. sometimes as much as sixteen or seventeen degrees. This is mainly to be attributed to the ice brought down by it from the coasts of Greenland, and from the Strait of Davis. Where the Gulf Stream brushes the Great Bank of Newfoundland, the warm water of the current is about 8° higher than that of the ocean, but the water of the ocean exceeds that which covers the Great Bank by 25°. These different degrees of temperature, though existing so near one another, can never attain an equilibrium, because each of them proceeds from a cause which is peculiar, and whose influence at the same time is permanent. To this difference of temperature, perhaps, the fogs on the banks and the coast of Nova Scotia may be attributed. The Gulf Stream, being itself of considerable breadth, and covering besides with the warm water brought down by it large tracts of the sea on both sides of its course, forms a vast expanse of warm water in the centre of the North Atlantic. It extends from the 30th meridian to the 75th, and sometimes covers in breadth at the east end all the sea from 33° or 34° to 45° N. lat., but at its western extremity it contracts to about 160 or 170 nautical miles. It is accordingly 2000 miles in length, and, at a mean, 350 miles in breadth, and thus forms a more extensive surface than the Mediterranean Sea. This body of water contains, besides the stream itself, its counter-currents, offsets, overflowings, and deposits, the current itself possibly not occupying one-half of this space. The Mexican Sea may therefore be considered as a vast cauldron for heating water, which is distributed over the central parts of the North Atlantic. It cannot be questioned that such a vast expanse of warm water, from 8° to 10° above the temperature of the sea, must have a great effect on the surrounding sea and the adjacent countries. This point, however, has not yet been fully elucidated. It is only ascertained that the region of the Gulf Stream, more than any other part of the ocean, is subject to very violent storms, which are most frequent to the north of 32° and 33° N. lat. | Farther, it is not improbable that the mild climate by which the countries along the coast of the Atlantic Ocean are so favourably distinguished from those farther inland, is mainly due to the evaporation continually arising from the surface of this immense lake of warm water, just as the high temperature of the Mediterranean is supposed to contribute greatly to the very favourable climate of the countries on its shores. The Gulf Stream greatly affects the navigation of the Atlantic Ocean. Vessels bound from Europe to North America avoid it as much as possible, because it would create a delay of at least a fortnight if they were to stem it. They therefore either sail to the south or to the north of it, commonly the latter, their course being accelerated as soon as they approach the continent of North America by the counter-currents which run between the Gulf Stream and the coast. The Gulf Stream is now avoided even by vessels returning from the West Indies and the Gulf of Mexico, though by following its course they arrive four or five days sooner in Europe than those which avoid it. But it has been found by experience that such vessels suffer a damage in wear and tear, which is greater than can be compensated by the gain of a few days. The Gulf Stream, for nearly the whole breadth of the Atlantic, is navigated The North African or Guinea Current has its origin in the sea, between the southern coast of Ireland and Cape Finisterre in Spain, and it is difficult to determine its position more positively. It is, however, a known fact, that the whole body of water between Cape Finisterre and the Azores is in motion to the south and south-east, the western part running more southerly, and the eastern, lying towards the continent of Europe, more easterly. As far as Cape St. Vincent, it runs half a mile per hour, but from that promontory southward about three-fourths of a mile. To the south of Cape St. Vincent, the coast of Europe and Africa form as it were the pipe of a funnel; and here it is observed that the whole body of water between the above-named cape and Cape Cantin on the African coast, and as far westward as the 20th meridian, sets towards the Strait of Gibraltar, probably to supply the deficiency of the water caused in that close sea by the evaporation produced by its higher temperature, which is 50 or 6° above that of the ocean under the same latitude. From Cape Cantin to Cape Bojador (26° 7' N. lat.), the motion of the sea, for a distance of more than 300 nautical miles from the land, points nearly towards the shore; and the same direction is observed to Cape Blanco, 5° farther south, but in the latter space it extends only from 150 to 180 miles from the land. This current along the coasts of the Sahara, united to the westerly wind which continually blows in this sea, renders it extremely dangerous to the unwary navigator, and has been the cause of numerous shipwrecks. From Cape Blanco to Cape Verde, the current along the coast sets somewhat to the west of south, and identifies itself with the drift-current of the trade-winds; but it does not mingle with it, as is indicated by the lower temperature of its water, which near the Cape de Verd Islands is 8° lower than that of the ocean moved by the drift-current. At the Cape Verde Islands it turns slowly round towards the south, and afterwards towards the S.E. and E.S. E., influenced by the form of the coast of Africa. Between Cape Verde and Cape Mesurado, the distance of the current from the shore is about 200 nautical miles, and this space is occupied by periodical currents. Having passed Cape Mesurado, the current sets due east, and runs here with increased rapidity, sometimes at the rate of two miles per hour. It ranges along the coast of Guinea, until it is partly dissipated in the sea opposite the mouth of the Quorra, between the Bay of Benin and of Biafra, and partly stopped foundland in a northerly direction along the Labrador shore, generally preventing all access to land, as high as the mouth of the Hudson Strait; then turning to the north-eastward, it forms a bay near the coast of Greenland in about 66° or 67° lat., by suddenly passing away to the southward to the southern extremity of Greenland. But this bay usually formed by the ice at 66° or 67° lat. does not always exist. The quantity of ice on each side of Davis's Strait is often small, and then the continuity of the a-head by the Equatorial Current. The Guinea Current extends along these coasts, at a mean, about 180 miles, or 3° | in breadth; and its greatest velocity is during the season of the S.W. winds (from June to September), in the sea lying west of Sierra Leone and south of the Cape Verde Islands. Its temperature is lower than that of the ocean by several degrees as far as the Cape Verde Islands, where the difference sometimes, as we have already observed, amounts to 8°; but to the south of these islands it receives a large accession of water from the westward, by which its tempera-ice-masses is liable to be broken, so as to allow ships to ture is raised at once several degrees. We conclude these observations on the currents of the Atlantic Ocean, by noticing that branch of the Guinea Current which separates itself from the main stream nearly at its origin, and passes to the east along the southern part of the Bay of Biscay. After coasting the northern shore of Spain, it turns to the N. and N.W. along the coasts of France, and shooting across the mouths of the English and Irish Channels, it bends round to the W. and thence through all the intermediate points to the S.E., till it falls again into the original current, performing a complete rotation between Spain, France, and the Atlantic at large. The N.E. side of this vortex shoots off to the N.W. and across the two channels, and thus forms the current which so often places ships in danger near the Scilly Islands. This current, the exact knowledge of which we owe to the indefatigable industry of the late Major James Rennell, bears his name, and is called Rennell's Current. It is commonly thought that the temperature of the southern hemisphere is considerably lower than that of the northern, and that the difference amounts at least to ten degrees of the scale of Fahrenheit. Baron Humboldt, who has collected and compared a great number of observations, thinks that near the poles and in very high latitudes such a difference and even a much larger one exists, but that not the least is to be observed between the tropics, and only a very small difference as far as the 35th and 40th parallel. His researches lead him to think, that from the equator to 34° lat., the winters are less cold in the southern than in the northern hemisphere, and even at the Falkland Islands (51° S. lat.) the month of July is milder than the January at London. Since Baron Humboldt published his researches, new observations have been made, especially by Captain Scoresby and Captain Weddell, from which it appears that the supposed difference between the temperature of both hemispheres in higher latitudes does not exist in the open sea, and it seems that most of the facts collected by Humboldt were made near the shores of America, which must powerfully influence the temperature of the adjacent sea. [See CLIMATE.] The fact, however, that the ice advances much farther to the south in the Northern, than to the north in the Southern Atlantic, deserves to be noticed more particularly. reach the land. It sometimes happens that the sea is The region of ice which surrounds the North Pole has not been attained, and therefore our information converning it is extremely scanty. Till lately, it was thought that all the ice extending from the Pole to a distance of about nine degrees, formed one continuous, undivided, and immoveable mass. But the attempt made by Captain Parry to reach the North Pole in the summer of 1827, shows that this apparently immense ice-field is divided into a great number of comparatively small pieces, and that these pieces, instead of being stationary, are continually on the move toward the south or south-west. It is, however, very probable that this condition of the polar ice was produced by the heat, which even in those high latitudes is considerable during the long day of the summer, and that with the return of the long night and the cold they are cemented together by the frost, and form one undivided mass. The pieces of ice, which in summer are detached from this mass, and move to the southward, probably by the impulse given to them by the Arctic Current, are carried along the eastern coast of Greenland to Cape Farewell in close masses, so that they only can be penetrated in the summer months with much labour and peril by bold navigators. In winter, they seem to be fixed to the coast, and to become stationary by the intensity of the frost, and even to extend over a part of the Atlantic which in summer is free from ice. The whale-fishers who annually visit the Spitzbergen Sea Similar changes take place in the ice of Hudson's Bay, and Davis's Strait find that these masses of ice form in the Baffin's Bay, and Davis's Strait. The navigation of the month of May an irregularly waving but generally conti- former bay is first interrupted by ice, generally in the nuous line from Newfoundland and Labrador to Nova Zembla. month of November; but on the east side of Davis's Strait it This continuous line of polar ice extends from New-does not usually make its appearance under the land until the spring. Little progress can be made through the ice It is very probable that the ice which is brought down by the Arctic current to the very centre of the North Atlantic, originates in the Bay of Baffin and the Strait of Davis; for it consists almost entirely of ice-bergs. When the sun returns to the arctic region, and the icy bonds which connect these bodies with the continent have been dissolved, they descend in numerous masses along the coasts of Labrador and Newfoundland, some of them entering the Gulf of St. Lawrence by the Strait of Belle Isle. From Newfoundland they advance farther to the south and southeast, and are often met with in the Gulf Stream itself, between 56° and 46° W. long., and as far south as 40° N. lat., from the month of April to that of November. Some of them even here are of vast size, but all in a state of rapid thaw. They cool the water sensibly to a distance of 40 or 50 miles around them; and the thermometer sinks sometimes no less than 17 or 18 degrees, from 61° or 60° to 43°, in their neighbourhood. In the southern hemisphere the ice does not advance to such low latitudes in any part of the sea. Captain Cook did not see any before he had passed the 50th or even the 52nd parallel; and Captain Weddell not before he reached 57 lat. Captain Weddell having found it in a rather crowded state between 59° and 69°, to the north and south of that chain of islands which are known under the names of the South Shetlands and New Orkneys group, arrived to the south of 70° lat. in an open sea, where not a particle of ice was found at 73° 17′ lat. and 35° 55′ long. W., and even at 74° 15' only a few ice-islands were met with. It therefore appears that the South Atlantic is much less encumbered with ice than the North Atlantic, probably because it contains much less land. Captain Cook observed, that the ice about the Antarctic Pole, in the South Atlantic, extended farther north than in the Pacific. Very few vessels, he says, met with ice going round Cape Horn, and very little is observed below the 60th degree of lat. in the Pacific. But between the meridian 40° W. and 50° or 60° E., it advances as far north as 51°. He hence inferred the existence of a southern continent. But it is now known that the ice found at this latitude owes its origin to the chain of islands above-mentioned, and to the extensive coast lately discovered in the neighbourhood by Captain Biscoe (Geogr. Journ. iii.), and that to the south of it the sea is open and entirely free of ice. a mantle, the surface of the sea for many miles, and extends for more than 1200 miles from north to south. The western region extends between the parallels 22 and 26, about the meridians of 70 and 72, where the weed also is found in a very crowded state. The intermediate region is less so; and it would even seem that in some parts the sea is only lightly strewed with it, whilst in others it is much more frequent. It is observed that the greatest mass of this weed is found at that part of the Atlantic where the Gulf Stream terminates; and the other great extent, where the counter-current of the Gulf Stream, which runs along its southern border, unites at the Bahamas with the driftcurrent of the North Atlantic. Much of this weed is brought down by the Gulf Stream from the Sea of Mexico; but the quantity is so great, that it is reasonably supposed that most of it must be produced in the Atlantic itself at the bottom of the sea. It is a known fact that the waters of the Atlantic Ocean, in different parts, contains different quantities of salt; and several persons have been at some pains to ascertain the amount of this difference, but no satisfactory results have yet been attained. We know only with certainty that the specific gravity of the sea-water is less near the poles than between the tropics and under the equator; but how great that difference is remains uncertain. Captain Scoresby found the specific gravity of the sea-water near the coast of Greenland to be between 10259 and 10270; and others have observed it between the tropics to be 1·0297, and near the equator even 1:0578; but the latter observation is rendered doubtful by others, which gave a different result. Another remarkable fact, which has been better ascertained, is the difference between the specific gravity of the water of the Baltic and Mediterranean Seas and the Ocean. That of the Baltic contains only one-sixth of the salt which is found dissolved in the Ocean, its specifie gravity being on an average not more than 10049. The Mediterranean Sea contains somewhat more salt than the Ocean: to the east of the Straits of Gibraltar, the specific gravity of the sea-water is 10338; whilst between Cape St. Vincent and Cape Cantin it was only found to be 10294. As to the Banks and Fisheries in the Atlantic, see the articles NEWFOUNDLAND, BERGEN FISHERY, WHALE FISHERY, &c. (Humboldt's Travels; Rennell's Investigation of the Currents in the Atlantic Ocean; Account of the Arctic Regions by Scoresby; Voyages of Cook, Ross, Parry, Scoresby, and Weddell.) ATLAS is the historical and geographical name of an extensive mountain-system, which covers, with its ranges, branches, and table-lands, the north-western part of Africa. Its southern boundary lies between 27° and 32° N. lat., from Cape Nun on the Atlantic Ocean to the Gulf of Cabes, or the Little Syrtis, opposite the island of Jerbi; the northern is formed by the southern coast of the Mediterranean Sea between Cape Spartel at the Straits of Gibraltar and Cape Bon, lying E.N.E. of the town of Tunis. The coast formed by its offsets and terraces along the Atlantic Ocean extends upwards of 600 geographical miles, and is partly low and sandy, and partly rocky, but does not rise to a great height, except at Cape Geer and a few isolated places of small extent. The coast along the Mediterranean between Cape Spartel and Cape Bon is generally rocky and high; in many places the elevation is very great, and it continues for a considerable extent. Between Cape Bon and the Gulf of Cabes it is likewise generally rocky to Cape Vada, but it does not rise here to a great height, and is in many places interrupted by a flat sandy shore. From Cape Vada to the island of Jerbi, along the Lesser Syrtis, it is extremely low and sandy. It may be considered as a peculiarity of the Atlantic Ocean, that a considerable part of its surface is covered with sargasso, or gulf-weed, fucus natans. The region of this weed extends nearly across the whole Ocean, beginning on the east at the 30th meridian, and extending on the west to the Bahama Islands. Its northern limit may be placed at 36° N. lat., and its southern at 19° N. lat. The whole region, however, is not equally crowded with weed, the greatest quantities being met with at the eastern and western extremities; on the east, nearly under the meridian of the islands of Corvo and Flores, the most western of the Azores, where, between lat. 25° and 36°, and long. 30° and 32°, it forms first a narrow stripe, but, to the south-ing to the system of the Atlas Mountains. ward, expands to a great width. This region is called by the Portuguese Mar de Sargasso, or weedy sea. The quantity of the weed is really astonishing. It covers, like The southern boundary of the Atlas is formed by the Great African Desert, or the Sahara; from which, as far as we know, it is separated by low sandy hills, which have been blown up by the winds, and which gradually encroach upon the gentle declivities with which the mountains terminate on this side. On the west of the Gulf of Cabes, the Nofusa Mountains, which are the last offset of the Atlas towards the east, are connected with the Ghuriano Mountains, which extend towards the S.E., through the kingdom of Tripoli, but for good reasons are considered as not belong Within the boundary here assigned to these mountains is comprehended the whole of the empire of Fez and Marocco, and that of the regency of Algiers, as well as the |