Waves and the Mode of their Formation.—Height and Velocity of Storm-Waves, on the High Seas, according to the Calculations of Scoresby, Arago, Sir James Ross, and Wilkes.—Their Height and Power on Coasts.—Their Destructive Effects along the British Shore.—Dunwich.—Reculver.—Shakspeare's Cliff.
After having admired the sea in the grandeur of its expanse, and the profundity of its depths, I shall, in this and the two following chapters, examine in what manner the perpetual circulation of its waters is maintained.
H.M.S. "Resolute" lying to in the North Atlantic.
"The movements of the sea," says Humboldt, "are of a three-fold description: partly irregular and transitory, depending upon the winds, and occasioning waves; partly regular and periodical, resulting from the attraction of the sun and the moon (ebb and flood); and partly permanent, though of unequal strength and rapidity at different periods (oceanic currents)."
Who has ever sojourned on the coast, or crossed the seas, and has not been delighted by the aspect of the waves, so graceful when a light breeze curls the surface of the waters, so sublime when a raging storm disturbs the depths of the ocean?
But it is easier to admire the beauty of a wave than clearly to explain its nature, so as to convey an accurate or sufficiently general conception of its formation to the reader's mind. Those who are placed for the first time on a stormy sea, discover with wonder that the large waves which they see rushing along with a velocity of many miles an hour do not carry the floating body along with them, but seem to pass under the bottom of the ship with scarcely a perceptible effect in carrying the vessel out of its course.
In like manner, the observer near the shore perceives that floating pieces of wood are not carried towards the shore with the rapidity of the waves, but are left nearly in the same place after the wave has passed them as before. Nay, if the tide be ebbing, the waves may even be observed rushing with great velocity towards the shore, while the body of water is actually receding, and any object floating in it is carried in the opposite direction to the waves out to sea.
What, then, is wave-motion as distinct from water-motion? The force of the wind, pushing a given mass of water out of its place into another, dislodges the original occupant, which is again pushed forward on the occupant of the next place, and so on. As the water-particles crowd upon one another, in the act of going out of their old places into the new, the crowd forms a temporary heap visible on the surface of the fluid, and as each successive mass is displacing the one before it, the undulation or oscillatory movement spreads farther and farther over the waters. Wave-motion is, in fact, the transference of motion without the transference of matter: of form without the substance, of force without the agent.
The strongest storm cannot suddenly raise high waves, they require time for their development. Fancy the wind blowing over an even sea, and it will set water-particles in motion all over the surface, and thus give the first impulse to the formation of small waves. Numberless oscillations unite their efforts, and create visible elevations and depressions. Meanwhile, the wind is constantly setting new particles in motion; long before the first oscillations have lost their effect, countless others are perpetually arising, and thus the sum of the propelling powers is constantly increasing, and gradually raising mountain-waves, until their growth is finally limited by the counterbalancing power of the earth's attraction.