Page:Physical Geography of the Sea and its Meteorology.djvu/78

52 Gulf Stream was sent across the Atlantic in contact with the solid crust of the earth—comparatively a good conductor of heat—instead of being sent across, as it is, in contact with a cold, non-conducting cushion of cool water to fend it from the bottom, much of its heat would be lost in the first part of the way, and the soft climates of both France and England would be, as that of Labrador, severe in the extreme, ice-bound, and bitterly cold.

144. Why should the Gulf Stream take its rise in the Gulf of Mexico?—That there should be in the North Atlantic Ocean a constant and copious flow and reflow of water between that ocean and the Arctic is (§ 107) not so strange, for there are abundant channel-ways between the two oceans. In one, water is to be found nearly at blood heat; in the other, as cold as ice. A familiar experiment shows that if two basins of such water be brought in connection by opening a water-way between them, the warm will immediately commence to flow to the cold, and the cold to seek the place of the warm. But why this warm flow in the Atlantic Ocean should seem to issue from the Gulf of Mexico, as if by pressure, is not so clear.

145. The trade-winds as a cause of the Gulf Stream.—To satisfy ourselves that the trade-winds have little or nothing to do in causing the Gulf Stream, we may by a process of reasoning, which ignores all the facts and circumstances already adduced, show that they cannot create a current to run when or where they do not blow. The north-east trade-winds of the Atlantic blow between the parallel of 25° and the equator; the Gulf Stream flows between the parallel of 25° and the North Pole.

146. Gulf Stream impelled by a constantly acting force.—A constantly acting power, such as the force of gravitation, is as necessary (§ 95) to keep fluids as it is to keep solids in motion. In either case the projectile force is soon overcome by resistance; and unless it be renewed, the current in the sea will cease to flow onward, as surely as a cannon-ball will stop its flight through the air when its force is spent. When the waters of Niagara reach Lake Ontario, they are no longer descending an inclined plane; there, gravity ceases to act as a propelling force, and the stream ceases to flow on, notwithstanding the impulse it derived from the falls and rapids above. A propelling power, having its seat only in the Gulf of Mexico, or the trade-wind region, could (§ 92) no more drive a jet of water across the ocean, than any other single impulse could send any other