Page:Physical Geography of the Sea and its Meteorology.djvu/243

Rh from the equator, at a mean temperature of 81°, is much greater than, according to the same laws, it ought to be. The observed difference of its specific gravity at 64° and 81° is .0015; whereas it ought to be .0025. Now as we approach the equator, the water is warmer, and it should therefore, were it of equal saltness, be proportionably lighter; but instead of the specific gravity of equatorial water being .0025 lighter—as by thermal laws it ought to be—than sea water at the temperature of 01° in latitude 34°, it is only .0015. What makes the equatorial water of the sea so much heavier than according to thermal laws it ought to be? Let us inquire:

435. An anomaly.—The anomaly is in the trade-wind region, and is best developed (Plate X., Fig. 2) in the North Atlantic, between the parallel of 40° and the equator. Though it is sufficiently apparent both in the North and South Pacific {Fig. 1)—it is masked by the Gulf Stream in the North Atlantic—commencing at the polar borders of these winds, the anomaly is developed as you approach the equator. The water grows warmer, but not proportionably lighter: this is in the trade-wind region. These winds evaporate as they go; but can it be possible that they are so regulated and adjusted, counterpoised and balanced, that the salt which they, by evaporation, leave behind, is just sufficient to counterbalance the dilatation due to the increasing warmth of the sea?

436. Influence of the trade-winds upon the specific gravity of sea water.—It is the trade-winds, then, which prevent the thermal and specific gravity curves from conforming with each other in intertropical seas. The water they suck up is fresh water, and the salt it contained, being left behind, is just sufficient to counter-balance, by its weight, the effect of thermal dilatation upon the specific gravity of sea water between the parallels of 34° north and south. As we go from 34° to the equator, the water grows warm and expands. It would become lighter, but the trade-winds, by taking up vapour without salt, make the water Salter, and therefore heavier. The conclusion is, the proportion of salt in sea water, its expansibility between 62° and 82° (for its thermal dilatability varies with its temperature), and the thirst of the trade-winds for vapour are, where they blow, so balanced as to produce perfect compensation; and a more beautiful compensation cannot, it appears to me, be found in the mechanism of the universe than that which we have here stumbled upon. It is a triple adjustment: the power of the sun to expand, the power of