252 THE PHYSICAL GEOGRAPHY OF THE SEA. 



dashing against the shore, the ebb and flow of the tides, may be re- 

 garded, in some sense, as the throbbings of the great sea pulse. 



547. The motions of the Gulf Stream (§ 53), beating time for 

 the ocean and telling the seasons for the whales, also suggest the 

 idea of a pulse in the sea, which may assist us in explaining some 

 of its phenomena. At one beat there is a rush of warm water from 

 the equator toward the poles, at the next beat a flow from the 

 poles toward the equator. This sort of pulsation is heard also in 

 the bowlings of the storm and the whistling of the wind ; the nee- 

 dle trembles unceasingly to it, and tells us of magnetic storms of 

 great violence, which at times extend over large portions of the 

 earth's surface ; and when we come to consult the records of those 

 exquisitely sensitive anemometers, which the science and ingenu- 

 ity of the age have placed at the service of philosophers, we find 

 there that the pulse of the atmosphere is never still : in what ap- 

 pears to us the most perfect calm, the recording pens are moving 

 to the pulses of the air. 



548. Now if we may be permitted to apply to the Gulf Stream 

 and to the warm flows of water from the Indian Ocean an idea 

 suggested by the functions of the human heart in the circulation 

 of the blood, we perceive how these pulsations of the great sea- 

 heart may perhaps assist in giving circulation to its waters through 

 the immense system of aqueous veins and arteries that run betw^een 

 the equatorial and polar regions. The waters of the Gulf Stream, 

 moving together in a body (§1) through such an extent of ocean, 

 and being almost impenetrable to the cold waters on either side — 

 which are, indeed, the banks' of this mighty river — may be com- 

 pared to a wedge-shaped cushion placed between a wall of waters 

 on the right and a wall of waters on the left. If now w^e imagine 

 the equilibrium of the sea to be disturbed by the heating or cool- 

 ing of its waters to the right or the left of this stream, or the freez- 

 ing or thawing of them in any part, or if we imagine the disturb- 

 ance to take place by the action of any of those agencies which 

 give rise to the motions which we have called the pulsations of 

 the sea, we may conceive how it might be possible for them to 

 force the wall of weiters on the left to press this cushion down to- 

 ward the south, and then again for the wall on the right to press 

 it back again to the north, as (^ 54) we have seen that it is. 



Now the Gulf Stream, with its head in the Straits of Florida, 



