THE DRIFT OF THE SEA. 323 



Thus this opening between the cold-water lobes appears to hold 

 to the chambers of the Indian Ocean, with their heated waters, 

 the relations which the valves and the ventricles of the human 

 h€art hold to the circulation of the blood. The closing of these 

 lobes at certain times prevents regurgitation of the warm waters, 

 and compels them to pass through their appointed channels. 



921. From this point of view, how many new beauties do not 

 now begin to present themselves in the machinery of the ocean I 

 its great heart not only beating time to the seasons, but palpitat- 

 ing also to the winds and the rains, to the cloud and the sun- 

 shine, to day and night (§ 864). Few persons have ever taken the 

 trouble to compute 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 its 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 At- 

 lantic 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 vapor, was left behind to disturb ecjui- 

 librium, weighed sixteen millions more of tons, or nearly twice as 

 much as all the ships in the world could carry at a cargo each. It 

 might fall in an hour, or it might fall in a day ; but, occupy what 

 time it might in falling, this rain 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 disturb* 

 ance in the equilibrium of the sea than would the fall of rain sup- 

 posed. 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 aver- 

 age for the year is (§ 208) sixty inches, but we will assume it for 

 the sea to be no more than thirty inches. In the aggregate, and 



