Page:The National geographic magazine, volume 1.djvu/62

 figures for mean velocity and temperature from surface to bottom are, it will be noticed, far below those for the surface current alone, where the velocity is often as great as five knots an hour, and the temperature as high as 80°. The indicated horse-power of a great ocean steamship—"La Bourgogne," "Werra," "Umbria" and "City of New York," for example—is from 9,000 to 16,000; that of some modern vessels of war is still greater; the "Vulcan," now building for the British Government, is 20,000, and the "Sardegna," for the Italian Government, 22,800. Again, if we convert into its equivalent horse-power the potential energy of the 270,000 cubic feet of water per second that rush down the rapids of Niagara and make their headlong plunge of 160 feet over the American and Horse-shoe falls, we get the enormous sum of 5,847,000. The Gulf Stream, however, is every hour carrying north through the straits of Florida fourteen and three-tenths cubic miles of water (more than three thousand times the the volume of Niagara), equivalent, considering the amount of heat it contains from 71° to 32° F., to three trillion and sixty three billion horse-power, or more than five hundred thousand times as much as all of these combined; indeed, considering only the amount of heat from 71° to 50°, it is still two hundred and seventy-five thousand times as great.

Sweeping northward toward Hatteras with its widening torrent, its volume still further increased by new supplies drawn in from the Bahamas and the northern coast of Cuba, its color a liquid ultramarine like the dark blue of the Mediterranean, or of some deep mountain lake, it then spreads northeastward toward the Grand banks of Newfoundland, and with decreasing velocity and lower temperature gradually merges into the general easterly drift that sets toward the shores of Europe about the 40th parallel.

The cold inshore current must also be considered, because it is to great contrasts of temperature that the violence of storms is very largely due. East of Newfoundland the Labrador current flows southward, and during the spring and summer months carries gigantic icebergs and masses of field-ice into the tracks of transatlantic steamships. Upon meeting the Gulf Stream, a portion of this cold current underruns it, and continues on its course at the bottom of the sea; another portion is deflected to the southwest, and flows, counter to the Gulf Stream, along the coast as far south as Hatteras.

The broad features of these great ocean currents have thus