The North Atlantic and Arctic seas form together a _cul de sac_ closed to the northward, for there is practically no passage for a body of water through Behring’s Strait. While, therefore, a large portion of the water, finding no free outlet toward the northeast, turns southward at the Azores, the remainder, instead of thinning off, has rather a tendency to accumulate against the coasts bounding the northern portions of the trough. We accordingly find that it has a depth off the west coast of Iceland of at least 4,800 feet, with an unknown lateral extension. Dr. Carpenter, discussing this opinion, says: “It is to me physically inconceivable that this surface film of _lighter_ (because warmer) water should collect itself together again--even supposing it still to retain any excess of temperature--and should burrow downward into the ‘trough,’ _displacing colder and heavier water_, to a depth much greater than that which it possesses at the point of its greatest ‘glory’--its passage through the Florida Narrows. The upholders of this hypothesis have to explain how such a recollection and dipping-down of the Gulf Stream water is to be accounted for on physical principles.” I believe that, as a rule, experimental imitations on a small scale are of little use in the illustration of natural phenomena; a very simple experiment will, however, show that such a process is possible. If we put a tablespoonful of cochineal into a can of hot water, so as to give it a red tint, and then run it through a piece of India-rubber tube with a considerable impulse along the surface of a quantity of cold water in a bath, we see the red stream widening out and becoming paler over the general surface of the water till it reaches the opposite edge, and very shortly the rapidly heightening color of a band along the opposite wall indicates an accumulation of the colored water where its current is arrested. If we now dip the hand into the water of the centre of the bath, a warm bracelet merely encircles the wrist; while at the end of the bath opposite the warm influx, the hot water, though considerably mixed, envelops the whole hand. The North Atlantic forms a basin closed to the northward. Into the corner of this basin, as into a bath--with a northeasterly direction given to it by its initial velocity, as if the supply pipe of the bath were turned so as to give the hot water a definite impulse--this enormous flood is poured, day and night, winter and summer. When the basin is full--and not till then--overcoming its northern impulse, the surplus water turns southward in a southern eddy, so that there is a certain tendency for the hot water to accumulate in the northern basin, to “bank down” along the northeastern coasts.