252 THE PHYSICAL GEOGRAPHY OF THE SEA. 
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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 between 
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 we 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 waters on the left to ipresss 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 Streani, with its head in the Straits of Florida, 
