Page:Africa by Élisée Reclus, Volume 3.djvu/37

TEMPERATURE— FAUNA. 21 Guinea waters, with which is mingled the discharge of the Niger and Congo, the two African rivers which have the greatest volume. In the South Atlantic regions also the water is less salt than in the neighbourhood of St. Helena, in consequence of the melting of the icebergs and floating ice brought by the oceanic currents from the Antarctic lands. These frozen masses penetrate farthest north in the months of June, July and August, that is, in the Austral winter season, when these fantastic glittering forms — domes, towers, obelisks — continually changing their outlines with the displacement of the centre of gravity, are met in the Cape waters, and even as far as 35° S. latitude. Farther south the ocean is strewn with myriads of floating fragments, which to vessels rounding the African continent present the appearance of an endless panorama of gorgeous palaces, temples, colonnades all aglow in the fiery rays of the setting sun. Temperature — Fauka. While diminishing the salinity, these icy crystals also considerably lower the temperature of the liquid masses flowing from the equatorial regions. Between the Cameroons and the Cape there is noticed on the surface a gradual decrease of heat, corresponding to that which also takes place in the atmospheric strata. The isothermal lines follow with considerable regularity from 82° F. on the Slave Coast to 59° towards the southern extremity of the continent. But in the deeper layers the vertical decrease down to the bed of the ocean presents some remark- able contrasts, due to the inflow from the broad Antarctic seas to the gradually narrowing Atlantic basin. Of these contrasts the most striking is the relatively low temperature of the equatorial waters. Taking the mean of the liquid mass lying under the equator between Africa and America, the average for the tepid surface and cool deep waters is found to be about 41° F., that is to say, con- siderably less than a degree higher than that of the tracts stretching to '63° S. latitude. On the other hand these same equatorial waters are fully four degrees colder than those of the north temperate zone under 33° N. latitude. This surprising contrast, attesting the great preponderance of the Antarctic over the Arctic current, occurs regularly in each of the isothermal zones between the two sections of the Atlantic tying north and south of the equator. At equal depths the greatest differences of temperature are recorded. Thus, under 33^ N. latitude, a sounding-line 500 fathoms long records a mean of about 50^ F., while at the same distance to the south of the equator the average is found to be only 39° F., showing a difference of eleven degrees between the two corresponding latitudes. The temperature falls slightly in the neighbourhood of the coast, owing to the steady influx of deep sea currents. In some places a difference of three degrees has been observed between the in-shore and outer waters within a distance of a few miles. The abrupt changes of temperature in the South Atlantic serve to limit the range of animal life, and to modify its outlines with the seasons. The deep-sea species living at. great depths in a uniform cold medium, can, of course, extend