Page:Physical Geography of the Sea and its Meteorology.djvu/434

408 757. Rains at sea and their effect upon its equilibrium.—Few persons have ever taken the trouble to compute (§ 402) how much the fall of a single inch of rain over an extensive region in the sea, or how much the change even of two or three degrees of temperature over a few thousand square miles of surface, tends to disturb its equilibrium, and consequently to cause an aqueous palpitation that is felt from the equator to the poles. Let us illustrate by an example: The surface of the Atlantic Ocean covers an area of about twenty-five millions of square miles. Now let us take one fifth of this area, and suppose a fall of rain one inch deep to take place over it. This rain would weigh three hundred and sixty thousand millions of tons; and the salt which, as water, it held in solution in the sea, and which, when that water was taken up as vapour, was left behind to disturb equilibrium, weighed sixteen millions more of tons, or nearly twice as much as all the ships in the world could carry at a cargo each. This rain might fall in an hour, or it might fall in a day; but, to occupy what time it might in falling, it is calculated to exert so much force—which is inconceivably great—in disturbing the equilibrium of the ocean. If all the water discharged by the Mississippi River during the year were taken up in one mighty measure and cast into the ocean at one effort, it, would not make a greater disturbance in the equilibrium of the sea, than would the supposed rain-fall. Now this is for but one fifth of the Atlantic, and the area of the Atlantic is about one fifth of the sea area of the world; and the estimated fall of rain was but one inch, whereas the average for the year is (§ 757) sixty inches; but we will assume it for the sea to be no more than thirty inches. In the aggregate, and on:an average, then, such a disturbance in the equilibrium of the whole ocean as is here supposed occurs seven hundred and fifty times a year,