THE ATLANTIC OCEAN ITS CURRENTS "There is a river in the ocean. In the severest droughts it never fails, and in the mightiest floods it never overflows. Its banks and its bottoms are of cold water, while its current is of warm. The Gulf of Mexico is its fountain, and its mouth is in the Arctic Seas. There is in the world no other such majestic flow of waters. Its current is more rapid than the Mississippi or the Amazon, and its volume more than a thousand times greater. Its waters, as far out from the Gulf as the Carolina coasts, are of an indigo blue. They are so dis tinctly marked that their line of junction with the common sea water may be traced by the eye. Often one half of the vessel may be perceived floating in Gulf-Stream water, while the other half is in the common water of the sea ; so sharp is the line, and such the want of affinity between those waters, and such, too, the reluctance, so to speak, on the part of the Gulf Stream to mingle with the common water of the sea." Thus the elo quent author of the " Physical Geography of the Sea " describes the celebrated Gulf Stream, the most wonderful and important of all the great currents of the ocean.
The north-east and south-east trade-winds, blowing steadily towards the equator, impart to the surface waters over which they blow a tendency in the same direction. The south west and north-west drifts thus produced meet in the tropics, and finally assume, and flow in, a westerly direction as the great equatorial current of the Atlantic. This immense flows from the African coasts towards Brazil with a velocity of from 20 to 60 miles a day, and an average surface temperature of 76°, or about 6° lower than the water which U. traverses. At first one hundred and sixty miles broad, it gradually widens to over four hundred miles as it approaches the South American coasts. Off Cape St. Roque it bifurcates; branch, the Guiana current, reinforced by the waters of the Amazon and the Orinoco, flows with a velocity of 18 miles a day at the surface, but of only 9 miles at its bottom, at a depth of 50 fathoms.' Entering the Caribbean Sea through the numerous passages between the islands of the Lesser Antilles, the now much-warmer waters press through the Channel of Yucatan, and proceed to make the circuit of the Gulf of Mexico, where, under a tropical sun, they acquire a still higher temperature and velocity, and finally flow through the Straits of Florida as the Gulf Stream. In the Channel of Florida the Gulf-Stream is thirty-two miles wide, and moves at the rate of four or five miles an hour, and has a mean temperature of 81° F. Thence it proceeds towards
Newfoundland in a direction almost parallel to the American coast, from which it is separated by a belt of cold water, the southerly prolongation of the Arctic current. The division between the two streams is so marked that a vessel may have her bows in warm, and her stern in cold, water. So abrupt is the change from a high to a low temperature, not only at the surface, but also to great depths, that off Massachusetts the line of separation, technically termed the " Cold Wall," is nearly perpendicular. There are also alternate streaks of warm and cold water in the stream itself, due most probably to the occasional "cropping up" of the cold under-water, and the " interlacing" at the surface of the cold water of the contiguous Arctic current with the warm water of the Gulf Stream. In its passage across the Atlantic, the latter gradu ally widens from 32 miles in the " Narrows," 150 miles off Charlestown, to 300 off Sandy Hook. In proportion to the increase in width it decreases in temperature and velocity. Starting with a velocity of from 70 to 120 miles a day, its speed is gradually abated, until south of the Grand Banks its waters are so diffused that its existence as a distinct current is entirely destroyed. The diffused but comparatively warm surface-water still preserves a perceptible easterly motion, and off the Azores merges partly into the sluggish north-easterly, and partly into the southerly, drifts. The former, generally re garded as the true " prolongation " of the Gulf Stream, extends to the British and Norwegian coasts, and is traceable even in Barents Sea and along the west coast of Greenland, thus form ing counter-drifts to the East Greenland and Davis' Strait currents respectively. But though the Gulf Stream may aid this north-easterly set of the Atlantic towards the Arctic basins, by a constant supply of warm water from the Mexican Gulf, still the drift which bathes the coasts of Britain and Norway, and ameliorates their otherwise rigorous climate, is most probably a part of the natural overflow of the warm waters of the tropics towards the poles, and would exist were there no Gulf Stream.' The portion directed into the Bay of Biscay, along the northern coast of the Spanish peninsula, is deflected thence to the north-west as Rennell's current.