322 THE PHYSICAL GEOGRAPHY OF THE SEA. 



ing of its waters to tlie riglit 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 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 (§ 56) we have seen that it is. 



919. Now the Gulf Stream, with its head in the Straits of 

 Florida, and its tail in the midst of the ocean, is wedge-shaped ; 

 its waters cling together, and are pushed to and fro — squeezed, 

 if you please — by a pressure (§ 55), now from the right, then from 

 the left, so as to work the whole wedge along between the cold 

 liquid walls which contain it. May not the velocity of this 

 stream, therefore, be in some sort the result of this working and 

 twisting, this peristaltic force in the sea ? 



920. In carrying out the views suggested by the idea of pulsa- 

 tions in the sea, and their effects in giving dynamical force to the 

 circulation of its waters, attention may be called to the two lobes 

 of polar waters that stretch up from the south into the Indian 

 Ocean, and which are separated by a feeble flow of tropical wa-> 

 ters. Icebergs are sometimes met with in these polar waters as 

 high up as the parallel of the fortieth degree of latitude. Now, 

 considering that this tropical flow in mid-ocean is not constant — 

 that many navigators cross the path assigned to it in the plate 

 without finding their thermometer to indicate any increase of heat 

 in the sea ; and considering, therefore, that any unusual flow of 

 polar waters, any sudden and extensive disruption of the ice there, 

 sufficient to cause a rush of waters thence, would have the effect 

 of closing for the time this mid-ocean flow of tropical waters, we 

 are entitled to infer that there is a sort of conflict at times going 

 on in this ocean between its polar and equatorial flows of water. 

 For instance, a rush of waters takes place from the poles toward 

 the equator. The two lobes close, cut off the equatorial flow 

 between them, and crowd the Indian Ocean with polar waters. 

 They press out the overheated waters ; hence the great equatorial 

 flow encountered by Captain Grant. 



