Page:Physical Geography of the Sea and its Meteorology.djvu/69

 Rh examination, that he had shot south—that is, to the right (§ 103) of his mark. In other words, that the path actually described by the ball would be a resultant arising from this difference in the rate of rotation and the trajectile force. Like a ray of light from the stars, the ball would be affected by aberration. The ball so shot presents the case of the passenger in the railroad car throwing an apple, as the train sweeps by, to a boy standing by the wayside. If he throw 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 target, for both the marksman and the passenger are going faster than the object at which they aim.

120. Tendency of all currents both in the sea and air to move in great circles a physical law.—Hence we may assume it as a law, that the natural tendency of all currents in the sea, like the natural tendency of all projectiles through the air, is to describe each its curve of flight very nearly in the plane of a great circle. The natural tendency of all matter, when put in motion, is to go from point to point by the shortest distance, and it requires force to overcome this tendency. Light, heat, and electricity, the howling wind, 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 obstruction, 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 will go, and continue to go—if on a plane, in a straight line; if about a sphere, in the arc of a great circle—thus showing that it has no volition except to obey impulse; and that impulse comes from the physical requirements upon it to take the shortest way to its point of destination.

121. This law recognized by the Gulf Stream.—The waters of the Gulf Stream, as they escape from the Gulf, are bound for the British Islands, to the North Sea, and Frozen Ocean (Plate IX.). Accordingly, they take (§118), in obedience to this physical 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 of the supposed cannon-ball.

122. Shoals of Nantucket do not control its course.—Many philosophers have expressed the opinion—indeed, the belief (§ 116) is