and this kind of motion is thus propagated throughout all the mill-pool.

Now this represents, on a small scale, a great natural phenomenon, called the Gulf Stream, because it was first observed in the Gulf of Florida, in the Atlantic Ocean. That particular current, however, is only part of an extensive circulation of all the waters in the great western basin.

To understand this, it must be observed that the waters of the open ocean, between the tropics, have a constant motion from east to west. This is seen very evidently at the Cape of Good Hope, where the waters of the great Indian Ocean unite with the Atlantic. There is a constant current setting from east to west, so that ships require a strong westerly wind to stem it: and many fatal accidents have happened by ships being driven upon the western coast of Africa, when they thought themselves many leagues to the east of it, from not allowing for the westerly current. The motion of the waters in the free ocean, would be at the rate of ten miles in the twenty-four hours, or about a quarter as fast as, upon an average, the principal rivers of Europe

run.

Now, upon casting an eye upon the map of the Atlantic, it will be seen that this great stream of water, coming from the ocean round the south of the Cape of Good Hope, will run in about a. orth-westerly direction, until it comes upon the great dam formed by the coast of South America. The waters of the Atlantic, between the tropics, are themselves impelled by the same causes which create this current, and in the same direction. so that a vast body of water, arising from the united action of those currents, is heaped up against the shores of South America. The strength of this current falls upon that part of the coast which is to the north of the river Parabiba, and by the direction of the coast is sent on, in nearly a north-westerly direction, past the mouths of the great rivers, Amazon and Orinoco, where the waters of the current enter the Carribbean Sea. The island of Trinidad is placed here just in the heart of the stream

and the waters pour between that island and the mainland with great rapidity, and then form a westerly current along the whole northern coast of South America. The effect of this current is seen in the distribution of land and water in that part of the globe. The islands of the West Indies seem to be those parts of a formerly connected Continent, which have strength enough to resist the continual force of the waves. And the Isthmus of Darien is, as it were, the backbone of a skeleton, of which the flesh and cartilages have been eaten away.

Along this isthmus the current of the western ocean is forced in a northerly direction; it meets with the turbid waves of the Mississippi, and proceeds to the southern extremity of Florida, so that its course is now turned nearly due east. Here it passes with great rapidity into the strait of Bahama, at the rate of eighty miles in twenty-four hours, or double the average rapidity of European rivers, and sometimes even with a velocity of five miles an hour, having now taken a nearly northeasterly direction.

We began by comparing the Gulf Stream to a millpool. To complete the resemblance at this point, we must suppose the stream which issues from the mill to be filled with hot water; for the great tropical current has been detained for a long time in the great hot gulf formed by the coast of Caraccas, the Mexican and Floridan coasts, and at length issues forth into the North Atlantic, at a temperature so greatly above the average heat of the ocean, that vessels navigating those seas, can tell within a few minutes the time of their entering the Gulf Stream by the sudden increase in the warmth of the water. This difference often amounts to nine, twelve, and fifteen degrees of Fahrenheit's thermometer, and sometimes to much more. Thus, on the banks of Newfoundland, the temperature of the cold water on the bank has been observed to be 50°, while that of the stream was 72°.

The breadth of the stream gradually increases after it leaves the straits of Bahama. Between Cape Biscaino

and the bank of Bahama, the breadth is fifteen leagues. In latitude 28° 30' N. the breadth is seventeen leagues. In latitude 41° 25′ N., longitude 67° W., it is eighty leagues wide; and having now met with a great arctic current, it is turned towards the east, at the southern extremity of the bank of Newfoundland, which Volney well denominates the bar at the mouth of this enormous marine river. The union of the hot current of water with the cold of the ocean and of the atmosphere is marked, at the bank of Newfoundland, by two phenomena. The current has expanded in width, and diminished in velocity. Hence, as in great floods, and at the mouths of rivers, the matter, which had been sustained in the water during its rapid motion, is now deposited, and in the course of years has formed the great bank of Newfoundland. Meanwhile, the water being relatively hot, the atmosphere which it brings with it contains copious vapours, which are precipitated, as soon as they meet with a colder current of air or water, and form those extraordinary banks of fog, which are, in the atmosphere of the bank of Newfoundland, what the bank itself is to the bottom of the ocean, a continual accumulation of matter brought from a distant region, to be there deposited.

The great current still continues onward to the east, and south-east to the Azores. At the westernmost of that group of islands it is a hundred and sixty leagues wide; and in latitude 33°, its southern edge is so near the northernly edge of the equinoxial current, running in the opposite direction, that a vessel cannot pass from one to the other in a day's sail. From the Azores, the current tends rather in a south-easterly direction, towards the straits of Gibraltar, the Madeiras, and the Canaries. It continues to set towards the African coast, between Capes Cantin and Bodojor. In latitude 25° 26' the current sets south, is afterwards turned to the south-west by the trending of the coast by Cape Blanc, and soon after is again mixed with the equinoxial current, and proceeds to run again the same course.

Thus, between the parallels of 11° and 44° N. latitude,

the waters of the Atlantic move in a perpetual round, as regularly as a mill-sluice: the waste being supplied by a constant influx of water from the Indian seas round the Cape of Good Hope. If a bottle were thrown into the sea it would return to the same point, unless retarded by accidental causes, in little less than three years, having completed a circuit of 3800 leagues, at the rate of rather more than ten miles a day. Such a bottle for instance, if sent adrift at the Canary Isles, would be floated to the coast of the Caraccas in thirteen months. Ten months more would take it round the Gulf of Mexico, and opposite the port of Havannah: and about forty or fifty days would then be sufficient to take it from the Gulf of Florida to the bank of Newfoundland : and perhaps ten or eleven months more would bring it to the coast of Africa.—Saturday Magazine.

CURIOSITIES OF PHYSICAL GEOGRAPHY.

THE depth of the ocean is very great in some places; for north of the Bermudas it was found to be nearly six miles. The pressure increases as we descend, and is so great that wood, which has been sunk to a considerable depth, has its pores penetrated with water to such a degree that it will no longer float. The ocean is darker than the darkest night in its lower regions; but in some part of the Arctic seas shells are clearly visible in four hundred and eighty feet of water; and in the West Indian seas the bottom is quite distinct at the same depth, the various hues of the submarine occupants of the ground being beautifully apparent. The true colour of the ocean is ultramarine, but every flitting cloud alters it, and organic and inorganic substances often tinge its waters: it is white in the Gulf of Guinea; black round the Maldives; vermillion off California; and so green in one place off the coast of Arabia that a ship has been seen to be in green water and blue at one time. Its saltness varies, the southern hemisphere

being more salt than the northern; but the water of the lake of Eltonsk, east of the Volga, contains the greatest proportion of saline matter, and is thereby rendered the most buoyant water known. The Dead Sea is so saturated with salt that it irritates the skin, and towards the south, pillars of this substance project from beds of sandstone. The waters of the Caspian are becoming more saline and smaller in quantity, because more water is evaporated than is supplied to it, though it receives large rivers and has no outlet. This sea is subject to heavy winds, which drive the waters over the land; a vessel was thus washed forty-six miles inland, and there stranded.

The highest known waves are seen off the Cape of Good Hope in a north-west gale; their greatest height is probably about forty feet from the trough of the wave to its summit. The tremendous breakers on the west coast of Ireland occasionally rise one hundred and fifty feet, and the Bell Rock lighthouse, one hundred and twelve feet high, is actually enveloped in foam, when there is no wind, by the ground swell. A dry wind raises the sea more than a wet one; but in a gale the water is probably calm two hundred or three hundred feet below the surface. Vast currents occur in various parts of the ocean, and tropical seeds are brought by them in abundance to the coasts of Ireland and the Hebrides. In some parts of the Carribbean Sea it is said that a boat may be kept at rest on the surface of a sweeping current by lowering a heavy body down to some depth, where another current, running in an opposite direction, neutralizes the power of the upper one to drift the boat along. Winds and currents cause a necessarily circuitous voyage from Jamaica to the lesser Antilles to take nearly as many weeks as it takes days to return.

Could the Russians pass over the pole and through Behring Straits to their North American settlements, they would save a voyage of about twenty thousand miles. Icebergs drift into the Atlantic two thousand miles from their starting place in the Arctic seas, and