44 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



common among mariners — that the coasts of the United States 

 and the Shoals of Nantucket turn the Gulf Stream towards the 

 east ; but if the view I have been endeavouring to make clear bo 

 correct, it w^ould appear that the course of the Gulf Stream is 

 fixed and prescribed by exactly the same laws that require the 

 planets to revolve in orbits, the planes of which shall pass 

 through the centre of the sun ; and that, were the Nantucket 

 Shoals not in existence, the course of the Gulf Stream, in the 

 main, would be exactly as it is and where it is. The Gulf 

 Stream is bound over to the North Sea and Bay of Biscay partly 

 for the reason, perhaps, that the waters there are lighter than 

 those of the Mexican Gulf ; and if the Shoals of Nantucket were 

 not in existence, it could not pursue a more direct route. The 

 Grand Banks, however, are encroaching (§ 116), and cold cur- 

 rents from the north come down upon it : they may, and probably 

 do, assist now and then to turn it aside. 



123. HersclieVs theory not consistent icith hnown facts. — Now if 

 this explanation as to the course of the Gulf Stream and its east- 

 ward tendency hold good, a current setting from the north 

 towards the south should (§ 103) have a westward tendency. It 

 should also move in a circle of trajection, or such as would be 

 described by a trajectile moving through the air without resist- 

 ance and for a great distance. Accordingly, and in obedience to 

 the propelling powers derived from the rate at which different 

 parallels are whirled around in diurnal motion (§ 91), we find 

 the current from the north, which meets the Gulf Stream on the 

 Grand Banks (Plate IX.), taking a south-iuestwardly direction, as 

 already described (§114). It runs down to the tropics by the 

 side of the Gulf Stream, and stretches as far to the west as our 

 own shores will allow. Yet, in the face of these facts, and in 

 spite of this force, both Major Eennell and M. Arago would 

 make the coasts of the United States and the Shoals of Nantucket 

 to turn the Gulf Stream towards the east : and Sir John Herschel 

 (§79) makes the trade-winds, which blow from the eastward, 

 drive this stream to the eastward ! 



124. The Channel of the Gulf Stream shifts ivith tlie season. — But 

 there are other forces operating upon the Gulf Stream. They 

 are derived (§ 80) from the effect of changes in the waters of the 

 whole ocean, as produced by changes in their temperature and 

 saltness from time to time. As the Gulf Stream leaves the coasts 

 of the United States, it begins to vary its position according to 



