The Gulf Stream cannot be viewed as a separate entity. Its very birth in the Gulf of Mexico depends on a great mass of water ever flowing from the south-east into the Caribbean Sea. Since so much water pours in, the same volume must pour out, and as it does so it gains the name of the “Gulf Stream.” But after quitting the Gulf of Mexico the stream does not exist alone. It becomes a leading part of the North Atlantic circulation. The whole surface of that ocean is slowly turning round and round--“whirling as if stirred in the direction of the hands of a watch,”[1] and the Gulf Stream occupies one side or more of the vast _maelström_. In the centre of this revolving mass of water lies a district where the motion is slight, and at that centre floats an enormous collection of drift and sea-weed called the Sargasso Sea. [1] Dr. H. R. Mill. Suppose we pour some water in a large basin, drop into it a handful of small leaves and chips, and make the whole spin gently with one hand. We shall then see how the chips and leaves will collect at the centre, and will float there, almost stationary. That is what happens, on a large scale, in the North Atlantic Ocean. Other Oceans also have this steady circular movement, not of the whole body of water, but of the surface-water, down to a greater or less depth--precisely how deep one cannot say; it lessens gradually with increasing depth. The same is found also in the South Atlantic, in the North and South Pacific, and doubtless in the Indian Ocean. To find its direction in any part, one need only lay a watch, face upwards, upon a map of the North Atlantic or the North Pacific. In both cases the water travels round _with_ the watch-hands. In the South Atlantic and the South Pacific the flow is just in the opposite direction. So both the Gulf Stream and the Black Stream are merely parts of a big oceanic whirlpool. Each ocean on Earth has its own system of circulation; and that system is part of a world-wide system. The waters are in perpetual and complicated motion. Streams pour incessantly hither and thither, to north and south, to east and west. Two vast streams, known as the Equatorial Currents, nominally pour round the world, but really are best seen in the open Pacific, where for long distances no land meddles with their career. They flow steadily westward, one to the north and one to the south of the equator. Between them flows a reverse stream, called the “Equatorial Counter Current.” If a certain amount of water travels north, an equal quantity must travel south. Or if, as in this case, so much water runs in a westerly direction, a corresponding amount has to run in an easterly direction. Water may be marvellously piled up here or there, by influences of land or of wind, but it cannot remain piled up, without efforts on the part of the ocean to restore the equilibrium.