44 THE PHYSICAL GEOGRAPHY OF THE SEA. 



througli the target. Like a raj of light from the stars, the ball 

 would be affected by aberration. 



49. It is the case of the passenger in the railroad car throwing 

 an apple, as the train sweeps by, to a boy standing by the way- 

 side. If he tlu'ow straight at' the boy, he will miss, for the apple, 

 partaking of the motion of the cars, will go ahead of the boy, and 

 for the very reason that the shot will pass in advance of the tar- 

 get, for both the marksman and the passenger are going faster 

 than the object at which they aim. 



50. Hence we may assume it as a law, that the natural tenden- 

 cy of all currents in the sea, like the natural tendency of all pro- 

 jectiles through the air, is to describe their curves of flight in the 

 planes of great circles. The natural tendency of all matter, when 

 put in motion, is to go from point to point by the shortest dis- 

 tance, and it requires force to overcome this tendency. Light, 

 heat, and electricity, running water, and all substances, whether 

 ponderable or imponderable, seek, when in motion, to obey this 

 law. Electricity may be turned aside from its course, and so 

 may the cannon ball or running water ; but remove every obstruc- 

 tion, and leave the current or the shot free to continue on in the 

 direction of the first impulse, or to turn aside of its own volition, 

 so to speak, and straight it wiU go, and continue to go — if on a 

 plane, in a straight line ; if on a sphere, in the arc of a great cir- 

 cle — thus showing that it has no volition except to obey impulse, 

 and the physical requirements to take the shortest way to its point 

 of destination. 



51. The waters of the Gulf Stream, as they escape from the 

 Gulf (§ 37), are bound for the British Islands, to the North Sea, 

 and Frozen Ocean (Plate IX.). Accordingly, they take (§ 47), in 

 obedience to this pliysical law, the most direct course by which 

 nature will permit them to reach their destination. And this 

 course, as already remarked, is nearly that of the great circle, and 

 exactly that of the supposed cannon ball. 



52. Many philosophers have expressed the opinion — indeed, the 

 belief (§ 46) is common among mariners — that the coasts of the 

 United States and the Shoals of Nantucket turn the Gulf Stream 

 toward tlie east ; but if the view I have been endeavoring to make 



