So much for the water of the sea; let us now see what it does. We will glance at the surface ere we plunge into the depths.
In childhood, and even in after years, we most of us delight in watching the waves of the sea. What finer sight than that we can obtain on the bold Cornish coast with a westerly wind, when the great Atlantic waves come rolling in and dashing up to the tops of the Tintagel cliffs, wearing and grinding them away; hissing up the sands at New Quay, or thundering on the shores of “Bude and Boss”! Then the wind abates, the sea goes down, the billows become waves, the waves to wavelets grow, less and less, until there is a mere ripple on the surface which is never still. The mighty heaving of the ocean breast is the peculiarity of the sea.
Fig. 698.—Sea waves.
Yet, again, as we stand to watch the waves, or run from them as they sweep in foam upon the sloping sand, we shall find that they increase or decrease in force, and the level of the water rises or sinks by degrees. The tide is flowing or ebbing as the case may be. So we know the surface has another—a current motion—besides the undulation of the water. The currents of the ocean are very valuable attributes, the Gulf Stream in particular bringing us warmth and, indeed, rain. There are three movements of the ocean—waves, currents, and tides.
The waves, perhaps, interest us most, as they come rolling in with irregular force, but all mightily impelled by the wind. We have all noticed the ripples on a puddle; the same action of the wind produces the grandeur of the waves of the ocean. The wave comes rolling in before the wind to break against the rocks or beach, and another forms to break in its place; the higher the waves the more quickly they appear to move. But when the wind has subsided the rolling, or “swell,” remains,—a long, lazy, undulating motion—a rocking to sleep of the billows of the sea. Without a ripple on the surface these huge rollers will glide towards the shore and break upon the shingle with a roaring sound which can be heard for miles, dragging the pebbles after them as they recede with a rattling like bones and marbles. The pebble ridge at Westward Ho! will illustrate this vividly at times, the sound being heard far inland like continuous thunder, and on a calm night, when there is no wind stirring, the roar of the ground swell is weird and mysterious in the gloom.
Fig. 699.—The Piroroco on the Amazon.
The height of waves is very varied. Observers say that forty-four feet is about the highest-known wave from hollow to crest. Waves of thirty-five feet have been often met with, and off the Irish coast and in the Atlantic sailors tell of waves “as big as houses.” But houses differ in size as do waves.
The rate which waves are estimated to travel varies with the wind-propelling force. The average hurricane wave travels at about forty-five miles an hour. But earthquake waves—those set in motion by subaqueous disturbance—have been known to travel at the rate of six hundred feet in a second for thousands of miles across the ocean. Such a one occurred after the earthquake which destroyed the town of Arica in August 1868, and the wave crossed the Pacific to Chetham Islands, 5,520 miles, in fifteen hours and twenty minutes. We have many of us seen the great tidal waves, or “bores,” which at certain seasons rush up our rivers—the Severn, for instance—with great violence, and at times forty feet high.