"A point or two off our course, I admit," replied the other; "but still we are going, and that is the great thing. We are not lying still like a log on the ocean." "How far have we run, sir, do you think, since last night?" I asked Captain Miles when Mr Marline made no further attempt at conversation. "I shall take a sight of the sun presently, my boy," he answered, with one of his odd winks, giving a quizzical glance at Mr Marline, as if telling me he thought he had shut him up for the time; "then I shall be better able to tell you. However, as we've been running twelve knots an hour good since four bells in the first watch, we ought to have made over a hundred miles or so from our last stopping place." "And where shall we get to if we continue running on the same as now?" I next inquired, thinking of what Mr Marline had said. "To the Banks of Newfoundland, I suppose, if the same wind holds; but, I'm of opinion that we'll have a change as soon as we fetch the Gulf Stream, when we shall be able to shape a straight course for the Channel." "And what is the Gulf Stream, captain?" I then asked. "Bless the boy!" he exclaimed, "I never saw such a chap for questions; why, you're almost as bad as Mr Marline! Well, if you must know, the Gulf Stream, or `Florida Current' as it is frequently called, is something very like a river of warm water, some eighty to three hundred miles wide, flowing through the surrounding ocean from the Gulf of Mexico to Europe in a circular nor'-east by east direction. Starting from between the Dry Tortugas and Cuba, it skirts the eastern shores of the United States, then passing across the Atlantic to the south of the Banks of Newfoundland, where it branches off into two currents in mid ocean, near the Azores. One of these streams steers north, along the shores of Norway, while the other leg sweeps onward to the English Channel, circling round the Bay of Biscay and then pursuing a southerly course along the Spanish coast until it meets the great equatorial current coming up from the south Atlantic. Uniting now with this, the double current flows back westwards to the place of its birth, only to renew its onward course again from the Caribbean Sea." "But what causes it?" I said.