Page:Africa by Élisée Reclus, Volume 3.djvu/25

 gradual, a difference of scarcely more than the fraction of a degree being observed in a layer several hundred fathoms thick. The result of two hundred and twelve soundings taken by the Talisman shows for depths of 500 fathoms a temperature of rather less than 50° F., or 27° degrees less than that of the surface waters; at 1,000 fathoms it oscillates round 39° F., at 2,000 fathoms it falls to 87°, at the bottom approaching 32°, which, however, for salt water is not the freezing point. In the region lying between the Azores and the Cape Verd group, the temperature on the bed of the ocean remains at 84° F. In the Bay of Biscay it is somewhat lower, and lower still towards the west, near the Antilles and Bermudas, and especially under the equator, whee the lowest in the Atlantic basin (32°5 F.) has been recorded.

Thus by a remarkable contrast the waters of the Azorian are found to be warmer than those of the equatorial Atlantic. In both regions the mean difference in corresponding

liquid volumes of 1,660 fathoms is about 8° 5' in favour of the northern section as far as 40° N. lat. This phenomenon, which seems opposed to the physical laws of the globe, must be attributed to the influence of the oceanic currents. While the region lying between the Antilles, the Canaries, and Cape Verd group is comparatively tranquil, and subject to the broiling heat of the sun, the equatorial waters are to a great extent constantly renewed on the surface by currents from the North Atlantic, which skirt the African seaboard along its whole length from north to south. At lower depths cold waters set steadily from the Antarctic regions along the bed of the West Atlantic to the north-east of the Antilles. According to the observations of the Challenger and Gazelle, these deep Antarctic currents meet in the zone to the south-west of the Azores, between 36° — 37° N. lat. The thermic equator of the oceanic bed, as indicated by warmer layers than those to the north and south, is thus deflected far beyond the geometric equator of the globe. It crosses the Azorian Atlantic obliquely, 1,200 miles to the north of the equator, so that on