The Sea and Its Work 



depressed in a little cup, and then rises again, the 

 motion being taken up by the neighbouring 

 water, and a succession of circles, each wider than 

 the last, spreads over the pond, until the ripples 

 at length die away upon the shore. If any light 

 object, such as a cork, happens to be floating on 

 the surface, it will serve to indicate the motion of 

 the water below. As the waves reach it, the 

 cork rises and falls, but it is not carried forward 

 by the movement of the water. Exactly the 

 same kind of action may be witnessed at sea. If 

 a gull, for example, is seated on a wave it is 

 simply rocked up and down, and not moved 

 onwards. 



Such simple observations are sufficient to show 

 that the motion of the water is a movement of 

 undulation and not of translation; it is merely 

 the form of the wave, and not the actual water, 

 that travels. The motion is transmitted from 

 particle to particle, to a great distance; but the 

 particles themselves perform very small excur- 

 sions, merely vibrating up and down, or rather 

 revolving in vertical circular paths. The general 

 effect is similar, as has often been pointed out, 

 to that witnessed when a gust of wind sweeps 

 across a field of corn. Nothwithstanding the 

 impression produced on the observer, he knows 

 that any movement of translation is here quite 

 out of the question; the stalks are not uprooted 

 and carried across the field, but each stalk simply 

 bends down before the wind and then returns to 

 its erect position. Similarly in the open sea, the 

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