The Book of the Ocean

by Ernest Ingersoll

As for gold and silver, both are present. I have seen it stated that a voyage of a year or two is sufficient to permit the formation of a film of silver all over the copper sheathing of a ship’s bottom, so that a frigate returning from a long cruise is really silver-plated; but I fancy this is more a matter of imagination than visible reality. Gold, in certain chemical combinations, certainly exists in sea-water, and may be extracted therefrom. Up to the present, however, the cost of the extraction has been more than the precious metal obtained was worth. Gold is often washed from sea-sand.

A FIORD, OR DEEP CREVICE WORN IN SEA-CLIFFS.

The ceaseless restlessness of the ocean forms another of the greatest contrasts between it and the immovable land—terra firma, as those like to call it who have been tossing too long on the “rolling deep”. This characteristic restlessness involves some of the most important and interesting facts in physical geography; for were the waters still,—that is, were the oceans simply huge, quiet ponds,—none of that action could take place along the shores which has been so important an agent in shaping the world and making it a suitable place for human habitation and social development.

On a planet with an atmosphere and changing seasons like ours, however, a stagnant ocean is as impossible as a motionless air; indeed, it is because the air is always in motion that large bodies of water are never at rest, for it is the changing density and temperature and movements (winds) of the air that produce waves and currents.

Waves are caused by the pressure and friction of the wind upon the surface of the water, as you may readily see at any pond; and the water in them simply rises and falls, driving forward a little at the very surface so as to cause a gentle current called wind-drift. When the waves approach the shallow, sloping border of the land they are checked at the bottom by the slope of the beach, while the freer upper part goes forward, and the waves speedily lose their rounded form and become more and more sharply ridged and steep on the front side as they sweep on until at last they pitch forward in the crash and thunder of surf.

In the open ocean the waves are usually doing little work except to cause the surface to rise and fall. The harder the wind blows, the higher the waves become, and the faster they travel. This speed has been calculated, and has been found to be proportionate to size.

“Waves 200 feet long from hollow to hollow,” we are told, “travel about 19 knots per hour; those of 400 feet in length make 27 knots; and those of 600 feet rush forward irresistibly at 32 knots.” These, of course, are under the furious impulse of a gale, and it is marvelous that ships can be made to ride over them; nor is it any wonder that excited mariners clinging to the bulwarks of some small and heeling craft, should call them “mountain high,” and declare in all seriousness that they have seen their crests rising one hundred feet above their hollows. No such altitude, nor half of it, probably, is ever reached by a storm-wave in the heaviest cyclone. An excellent authority, Lieutenant Qualtrough, assures us that the highest trustworthy measurements are from forty-four to forty-eight feet. The height of a wave depends upon what mariners call its “fetch”—that is, its distance from the place where the waves began to form. This has been worked out mathematically by Thomas Stevenson (father of the late Robert Louis Stevenson, the novelist), an eminent engineer and designer of lighthouses, who gives the following formula: “The height of the wave in feet is equal to 1½ multiplied by the square root of the fetch in nautical miles.” If the waves began 100 miles away from your ship, the waves about you will be 15 feet high, because the square root of 100 is 10, and one and a half times 10 is 15 (feet). The highest waves are not formed in the greatest tempests, which beat down their crests, but when the gale is both very strong and long continued. The worst “seas,” as sailors call big waves, are those met with off the Cape of Good Hope and Cape Horn.

The depth to which wave disturbance extends depends on the violence of the wind, and near shore upon the slope of the bottom. Prestwich tells us that pebbles may sometimes be moved at the depth of one hundred feet, and sand much deeper, as is shown by the fact that the bottom is disturbed in heavy storms on the Banks of Newfoundland.

The weight and power of such on-rushing masses of water are tremendous, as appears from the effect on coasts where they strike; but this opens up a subject which is too large for treatment here, and I must refer readers to geological treatises, and to such special works as Professor N. S. Shaler’s excellent “Sea and Land,” where the work of the ocean in tearing down and building up its coasts is fully and entertainingly explained. I shall have something more to say on this point, also, when I come to the chapter “Dangers of the Deep,” and speak of the terrible destruction caused by earthquakes, and in certain other agitations of the sea not due to the wind, and often styled “tidal waves.” There is only one kind of “tidal wave,” properly speaking, however; and this is a theoretical rather than an actual one, perceptible usually only in that rising and falling of the water along coasts twice each twenty-four hours that we call the flow and ebb of the tides; and here we see the effect rather than the thing itself.