From the diffused warm-water area which marks the termination of the true Gulf Stream, there is also a southerly drift between the Azores and the coast of Spain. The North African current thus formed, being deflected by the north western coast of Africa, sweeps to the south-west, and bifur cates off Cape Verd, the main portion curving towards, and finally joining, the North Equatorial current; the rest, bending round the African coast as the Guinea current, are also swept to the west with the South Equatorial current. Now, wherever a circular motion is given to any area of water, all the floating substances in that area will accumulate together near the centre, where the motion is less felt.. In the North Atlantic, the inner portions of the Equatorial current, Gulf Stream, and African current form a continuous revolving current, enclosing an area of not less than 10,000 miles in circumference of comparatively still, and near the centre absolutely stagnant, water. The effect of the circular motion imparted by the great currents mentioned, is to "slough off" the drift-wood and sea-weed, and other floating debris, towards the centre, and thus the vast area known as the Sargasso Sea has been formed. It is so thickly matted with weeds (chiefly Fucus Natant° that the speed of vessels passing through it is much retarded. But the Gulf Stream, and pro bably the other currents also, vary their position according to the season, the northern limit of the Gulf Stream being in winter about 40° to 41° N. lat., and in summer from 45° to 46°. Similarly, the limits of the Sargasso Sea vary according to the seasons, the storms, and the winds, but its mean position year after year is the same. Areas of comparatively still or stagnant water are also found in all the other great oceans— in fact, wherever there are return currents.
Whether the north-easterly drift between the Icelandic and Norwegian coasts be a direct prolongation of the Gulf Stream, or a natural flow of the warm tropical waters towards the pole, the climatical influence of the Gulf Stream is un doubtedly great. This vast current, the greatest and most important "river in the ocean," conveys into the temperate zone of the Atlantic an amount of heat equal to one-fourth the total amount received by the whole area of that ocean from the sun. Let the Gulf Stream be stopped, therefore, and the North Atlantic would be instantly deprived of at least one-fourth of its supply of heat, with what result to the now habitable and flourishing states of Western Europe may be imagined. The iceberg-laden Arctic currents would then pour their glacial waters far south into the Atlantic, and so chill the overlying air, that the westerly winds, instead of being, as at present, moist and warm, would be piercingly cold.
As regards the course of the Gulf Stream, it neces sarily issues due north from the Straits of Florida ; and were the earth stationary, and the ocean uninterrupted by land, it would preserve a due north course towards the Polar Sea. But its actual course is to the north-east. Looking at its general parallelism to the shores of the United States, a hasty •observer would most probably infer that they are the cause of the easterly deflection of the stream. Were it so, its warm waters would most certainly bathe the American coasts from Florida to Newfoundland. Is this the case 1 No. From Newfoundland to Cape Hatteras, if not beyond, there is a shore-belt of cold water from the north, the southerly pro longation of the Labrador current. The north-easterly course of the Gulf Stream is due to the modifying influence of the earth's diurnal rotation, owing to which all currents from these tropics to the poles have an easterly tendency ; and, conversely, all currents from the poles towards the equator incline to the west.' As regards the cause of the Gulf Stream, it is improb able that—although the joint effect of the north-east and south-east trades may be the primum mobile of a surface drift, as the Equatorial current virtually is—such a vast, constant deep-sea current as the Gulf Stream can be produced or im pelled by the mere "piling up" of the water in the confined area of the Mexican Gulf For it is evident that, were this the sole cause of the current, it would, as soon as it emerged from the Narrows and found sea-room, spread itself broadly out almost in the immediate neighbourhood, and most certainly would not hold on its way, furrowing the ocean for three thousand miles, a veritable "river in the ocean." Be
sides, if the trade winds be directly or indirectly the cause of the Gulf Stream, how is it that another current runs side by side with it along the American coast in an exactly oppo site direction 7 Assuredly the winds that prove powerful enough to produce a constant current of such a magnitude and velocity as the Gulf Stream, would hold in check, if not altogether deflect, the comparatively sluggish flow from the north. If, therefore, the winds alone are the cause of all cur rents, it is most remarkable that there should be in the same area two contiguous currents flowing in exactly opposite directions. The Gulf Stream, therefore, is not, and could not possibly be, produced by winds alone, even if much more stronger and continuous than the trades, but is simply the natural overflow of the heated waters of the tropics towards the poles, thus compensating the influx of polar waters towards the equator—a circulation due, as we have already remarked (Art. 129), to differences in specific gravity or density, arising from differences of temperature and sali nity, and which would exist were there no aerial currents whatever.
The Gulf Stream, with its heated waters, contrasts strongly with the cold, iceberg-laden Arctic Current. Two well-defined currents set out from the north polar regions into the Atlantic. The East Greenland current, flowing in a southerly direction between Iceland and Greenland, unites off Cape Farewell with the Davis Strait current, coming from Baffin Bay. The united streams flow south as the Labrador current, and after sending a minor stream into the Gulf of St. Lawrence through the Strait of Belle-Isle, curve round New foundland, and off the Grand Banks meet with the warm current from the Mexican Gul£ Being heavier, one portion of the Arctic current sinks below the Gulf Stream, and enters the Caribbean Sea as an under-current The other portion turns to the south-west, and proceeds towards Florida as the United States counter-current—thus flowing side by side with the Gulf Stream, but in an exactly opposite direction. "The Arctic current thus replaces the warm water sent through the Gulf Stream, and modifies the climate of Central America and the Gulf of Mexico,—which, but for this beautiful and benign system of aqueous circulation, would be one of the hottest and most pestilential in the world." The southern portion of the great Equatorial current, deflected to the south-west off Cape St. Roque, becomes the Brazil current of the South Atlantic Ocean. Flowing at a distance of about 250 miles from the its initial velocity of 25 miles a day is greatly reduced by the cross stream of the La Plata, and is finally arrested by the Cape Horn current. Before crossing the La Plata, however, the larger portion of this current seems to be deflected due east as the Southern connecting current, and either curves to the north past the Cape of Good Hope—thus uniting again with the South Equatorial current, as a part of the Gulf Stream does with the northern portion of the same current--or is continued into the Indian Ocean, thus forming part of an easterly drift extending from the La Plata to New Zealand. Such are the principal currents of the Atlantic Ocean, distinguished from those of the Indian and Pacific currents not only by a greater velocity, and a generally more marked character, but also by their importance in the navigation of the stormiest but most frequented of all the great oceans, and their influence in modi fying the climates of countries bordering upon it. And when we reflect that these countries are mainly inhabited by the most civilized nations of the earth, the part played by this ocean in the promotion and diffusion of a higher civilization is surely worthy of careful consideration and earnest study.