Page:Physical Geography of the Sea and its Meteorology.djvu/498

472 temperature raised high by day and cooled low down by night; but the most powerful sun, after beating down all day with its fiercest intensity upon this liquid covering, has not power to raise its temperature more than three or four degrees. This covering serves as a reservoir for the solar heat. In the depths below it is concealed from the powers of intense radiation, and held by the obedient ocean in readiness to be brought to the surface from time to time, and as the winds and the clouds call for it. Here it is rendered latent by the forces of evaporation, and in this form, having fulfilled its office in the economy of the ocean, it passes off into the air, there to enter, in mysterious ways, upon the performance of its manifold tasks.

890. Actinic processes.—As evaporation goes on by day or night, the upper stratum is rendered heavier by reason of both the heat and the fresh water borne away by evaporation; the upper water having been thus rendered both Salter and cooler, has its specific gravity increased so much the more. On the other hand, the strata below, receiving more heat by day than they dispense again by radiation day and night, grow actually warmer and specifically lighter; and thus, by unseen hands and the "clapping of the waves," the waters below are brought to the surface, and those on the surface carried down to unknown depths; and thus, also, we discover new and strange processes which have been ordained for the waters of the ocean in their system of vertical circulation.

891. The reservoirs of heat.—Thus we arrive at the conclusion that the ocean is the great reservoir of sensible as the clouds are of latent heat. That in those two chambers it is innocuously stored, thence to be dispensed by processes as marvellous as they are benignant and wise, to perform its manifold offices in the economy of our planet; it is this heat which gives "his circuits" to the winds and circulation to the sea; it is it that fetches from the ocean the clouds that make "the earth soft with showers." Stored away in the depths of inter-tropical seas, it is conveyed along by "secret paths" to northern climes, there to be brought to the surface in due season, given to the winds, and borne away to temper the climates of western Europe, clothing the British Islands as they go, in green, and causing them to smile under the genial warmth even in the dead of winter.

892. An office for waves in the sea.—Thus perhaps we discover a new office for the waves in the physical economy of the ocean.