Page:Physical Geography of the Sea and its Meteorology.djvu/245

Rh velocity. How much, if to any extent, the former warm climates of the British. Islands and Northern Asia may be due to such a warm covering of the sea, may perhaps, at some future time, be considered worthy of special inquiry. We have already seen (§ 434) that there is something else besides temperature that is at work in effecting changes in the specific gravity of sea water. Whatever increases or diminishes its saltness, increases or diminishes its specific gravity; and the agents that are at work in the sea doing this are sea shells, the rivers, and the rains, as well as the winds. Between 35° or 40° and the equator evaporation is in excess of precipitation; at any rate, there is but little precipitation except under the equatorial cloud-ring (see Storm and Rain Chart, Plate XIII.); and though, as we approach the equator on either side from these parallels, the solar ray warms and expands the surface water of the sea, the winds, by the vapour they carry off and the salt they leave behind, prevent it from making that water lighter.

438. Nicely adjusted.—Thus two antagonistic forces are unmasked, and, being unmasked, we discover in them a most exquisite adjustment—a compensation—by which the dynamical forces that reside in the sunbeam and the trade-wind are made to counterbalance each other; by which the climates of intertropical seas are regulated; and by which the set, force, and volume of oceanic currents are measured. This compensation is most beautiful; it explains the paradox (§ 434), gives volume to the harmonies of the sea, and makes them louder in their song of Almighty praise than the noise of many waters. Philosophers have admired the relations between the size of the earth, the force of gravity, and the strength of fibre in the flower-stalks of plants (§ 303), but how much more exquisite is the system of counterpoises and adjustments here presented between the sea and its salts, the winds and the heat of the sun! The capacity of the sun to warm, of the sea water to expand, the quantity of salts these contain, and the power of the wind to suck up vapour, are all in such nice adjustment the one with the other, that there is the most perfect compensation. By it they make music in the sea, and the harmony that comes pealing thence, though not of so lofty a strain, is nevertheless, like the songs of the stars, divine.

439. A thermal tide.—Suppose there were no winds to suck up fresh water from the brine of the ocean; that its average depth were 3000 fathoms; that the solar ray were endowed with power to penetrate with its heat from the top to the bottom; and that.