THE GULF STREAM. 45 



clear be correct — and I think it is — it appears 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 Nan- 

 tucket 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 J^orth Sea and Bay of Biscay partly 

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

 those of the Mexican Gulf (§ 37) ; and if the Shoals of Nantucket 

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

 The Grand Banks, however, are encroaching (§ 4G), and cold cur- 

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

 do, assist now and then to turn it aside. 



53. Now if this explanation as to the course of the Gulf Stream 

 and its eastward tendency hold good, a current setting from the 

 north toward the south should (§ 21) 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 resistance 

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

 propelling powers, derived from the rate at which different paral- 

 lels are whirled around in diurnal motion (§ 16), we find the cur- 

 rent from the north, which meets the Gulf Stream on the Grand 

 Banks (Plate IX.), taking a ^ouihicestwardly direction, as already 

 described (§ 45). 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 make the coasts of the 

 United States and the Shoals of Nantucket to turn the Gulf 

 Stream toward the east. 



54. But there are other forces operating upon the Gulf Stream. 

 They are derived from the eftect of changes in the waters of the 

 whole ocean, as produced by changes in their temperature from 

 time to time. As the Gulf Stream leaves the coasts of the United 

 States, it begins to vary its position according to the seasons ; the 

 limit of its northern edge, as it passes the meridian of Cape Race 

 (Plate YI.), being in winter about latitude 40-41°, and in Sep- 

 tember, when the sea is hottest, about latitude 45-46°. The 



