ZQ THE PHYSICAL GEOGRAPHY OF THE SEA. 



Winter temperature wintei's day, off Hatteras, and even as high up as 

 of the Gulf stream. ^|^g Qxmd Banks of Newfoundland in mid-ocean, a 

 difference between its waters and those of the ocean near by of 20°, 

 and even 30°. Water, we know, expands by heat, and here the 

 difference of temperature may more than compensate for the dif- 

 ference in saltness, and leave, therefore, the waters of the Gulf 

 Stream, though Salter, yet lighter by reason of their warmth. 



110. If they be lighter, they should therefore occupy a higher 

 Top of Gulf stream l^vcl than thosc through which they flow. Assum- 

 roof-shaped. -j^g ^|^q dcpth off Hattcras to be one hundred and 

 fourteen fathoms, and allowing the usual rates of expansion for 

 sea water, figures show that the middle or axis of the Gulf Stream 

 there should be nearly two feet higher than the contiguous waters 

 of the Atlantic. Hence the surface of the stream should present 

 a double inclined plane, from which the water would be running- 

 down on either side as from the roof of a house. As this runs 

 off at the top, the same weight of colder water runs in at the bot- 

 tom, and so raises up the cold-water bed of the Gulf Stream, and 

 causes it to become shallower and shallower as it goes north. That 

 the Gulf Stream is therefore roof-shaped, causing the waters on its 

 surface to flow off to either side from the middle, we have not 

 only circumstantial evidence to show, but observations to prove. 

 Navigators, while drifting along with the Gulf Stream, have low- 

 ered a boat to try the surface current. In such cases, the boat 

 would drift either to the east or to the west, as it happened to be 

 on one side or the other of the axis of the stream, while the ves- 

 sel herself would drift along with the stream in the direction of 

 its course ; thus showing the existence of a shallow roof-current 

 from the middle toward either edge, which would carry the boat 

 along, but which, being superficial, does not extend deep enough 

 to affect the drift of the vessel. 



111. That such is the case (§ 110) is also indicated by the 

 Drift matter Biough- circumstaucc that the sea- weed and drift-wood 

 edoflf to the right. ^]^{q\^ qj^q found in such large quantities along the 

 outer edge of the Gulf Stream, are rarely, even with the preva- 

 lence of easterly winds, found along its inner edge — and for the 

 simple reason that to cross the Gulf Stream, and to pass over from 

 that side to this, they would have to drift up an inclined plane, as 

 it were ; that is, they would have to stem this roof-current until 



