It has usually been held that the gulf stream extends across the Atlantic to the shores of northern Europe, and is the cause of the mild and moist climate enjoyed by the Western parts of that continent. The opinion, however, is beginning to prevail that, as a distinct current, the gulf stream ceases in the middle of the n. Atlantic, its waters being by time thinned out to a mere film, and its initial velority and dis tinctive heat having been dissipated. That warm waters from tropical seas are brought to the coasts of Britain, and even into the polar seas beyond, is proved by drift-wood, seeds, and fruits from the West Indies being frequently cast ashore on the Hebrides, the n. of .Norway, and Spitzbergen. But this is accounted for by the general flow of the surface-water towards the poles, forming part of the vertical oceanic a flow which receives an eastward deflection as it proceeds northwards, in the way above explained. This general set of the surface-water is further promoted by the prevalence of south-westerly winds, which maintain a pretty constant n.e. drift over the,whole sur face of the north-eastern portion of the Atlantic. In this way, although the gulf strewn may have lost its original impetus, a large portion of the super-heated water which it brings into the center of the Atlantic is carried to the shores of Europe and into the Arctic sea.
The Pacific ocean has also its great equatorial or trade-wind Current, but there is no great basin like the gulf of Mexico to gather the waters of another gulf stream. A portion of the equatorial current passes northward along the shores of China and Japan; a portion passes through the narrow channels of the Indian seas, and another portion turns southward towards Australia and New Zealand, affecting, douhtless, the isothermal lines in those latitudes, and returning in counter-currents to cape Horn, and even passing around it into the Yitlautic. While thus a portion of the great counter or polar' current of the south Pacific sweeps around cape Horn, another portion passes up the western coast of South America across the equator to 5° n. lat.; and its coolness is sensibly fell, and was carefully observed by baron Humboldt on the coast of Peru. The currents in ,the waters between the Pacific and. Indian oceans are also variously affected by the monsoons, and in some plabes run six months in one direction, and six months in the opposite, clearly proving that they are mainly dependent upon the direc tion and force of the winds. A chart of ocean currents was published by the admi ralty in 1872 which proves beyond a doubt that it is almost wholly to the prevailing winds we 'mist look for an explanation of ocean currents, At first sight it appears incredible that a- current of water should force its way through the ocean with sharply defined boundaries, and a peculiar color, ternperatur e, and inhabitants, like a great river flowing between its banks, for thousthids of miles and against the force of countercurrents, which even cross its course, passing under by their superior density, until it loses its on the shores of distant continents, or spreads out its warm flood on the bosom of northern seas. But a closer observa
tion will satisfy us that all this is in accordance with the laws of hydrodynamics. At the confluence of the clear waters of the Mississippi with the turbid current of the Missouri, the two rivers do not at once unite, but run ride by side with a sharply at fined boundary between them for many a league. So great rivers running into the ocean, are rivers still, far out at sea. the current of the Rio de is Plata, which drains the southern portion of South America, can lie perceived 200 In. from land; and the Amazon sweeps far into the Atlantic, though gradually bent northwardly Iv the great trade wind current, and then carried along the coast, to help, with the Orinoco, to swell the waters of the gulf of Mexico; so that the waters of the Amazon, the Orinoco, the Rio Gmnde, arid the Mississippi, all join to swell the gulf stream.
The channel of the gulf stream in its narrower portion is of great depth. From obser vations made by the Challenger in 1873, in that part of•the stream between Bermuda and New York, it is seen the gulf stream is there about 1C0 fathoms deep,'and, 80 tn. in width. The probability of its having hollowed out for itself a well-defined channel like the lied Of a river, is shown by a sudden increase of depth at its border, where deep-sea soundings have been made; hut so little can be known of the effect of cur rents upon a line of 20,000 ft. in 'crag'', and which require several hours to run off the reel, that we cannot place implicit reliance on such observations.
More important observations on the courses and influence of these currents have been Ittely undertaken by dropping bottles containing the date, latitude, and longitude, in all parts of the ocean. These bottles, when found upon the coast- thousands of miles distant, give some indication of the direction and velocity of the currents that have brought them; but such testimony is not infallible. The bottle may be imprile'l br contrary winds, blown into counter-currents, or whirled about for months in eddies. A bottle thrown overboard in the Indian ocean might reach the island of Spitzbergen, the gulf of Mexico; but there are many chances that it would be thrown out of the regular current, and be picked up on the shores of New Zealand or the mast of Peru. Dr. Franklin's Ilaritilae Obserratioug, Pownall's Hydraulic and Nautical Olmerraeions, ilumboldt's Atlas Geographigne et Phygigue„Tobnston's Phyeical Atlas, Ma aryls Phyrica Geography of the Seas, and Wind and Current Charts, and admiralty wind and current charts for Pacific, Atlantic, and Indian oceans.