THE MAELSTROM, CHARYBDIS
AND HELL GATE
Differences in level, produced by high tides, cause currents which vary in force and direction with the condition of the tide, producing, in some cases, dangerous whirlpools. The famous Maelstrom, off the coast of Norway, is but a tidal current, which rushes with great violence between two of the Lofoden Islands, causing a whirling motion in the water which is reversed at each ebb and flow of the tide.
Such is, also, the famous whirlpool of Charybdis, in the Straight of Messina, and many others of less note. The powerful currents of Hell Gate, in the passage from Long Island Sound to New York Bay, are due to a similar cause, high water occurring at different hours in the bay and in the west end of the sound.
WHAT CAUSES THE WAVES
OF THE OCEAN
The waves of the ocean, which are caused by the action of the wind, and which are called secondary or wind waves are of a totally different character from the tidal wave. The influence of the wind is supposed not to extend to a greater depth than forty or fifty feet, the deep sea, though raised in a great mass by the grand tidal movement, being free from agitation. Wind waves at a distance from the shore are comparatively low and long, but in shoal water they assume a greater curvature, and fall on the beach either in gentle ripples or in mighty breakers, according to the depth of the water and the force of the wind. The heavy swell which occasionally takes place, called the “ground sea,” is supposed to originate in distant storms of wind.
THE RIVERS IN
THE SEA
Currents in the ocean arise from various causes. They may be produced by long-continued gales of wind, by the melting of polar ice, or by any cause that may give rise to onward movements of limited portions of the great mass of waters. Other currents, and of these only is it necessary to speak in this connection, are permanent. The most remarkable of these are the polar currents and the equatorial currents.
Polar Currents are produced by the perpetual movement of the waters from the poles to the equator. In accordance with the laws of mechanics, an accumulation of the waters takes place on that part of the globe which has the greatest velocity of motion; and as the earth in turning on its axis moves with far greater velocity at the equator, the waters continually flow toward that line from the poles.
Equatorial Currents. This accumulation of the waters at the equator tends to produce the equatorial currents, which consist of the continuous progression of the tropical seas in a westerly direction. When the wave brought by the polar currents arrives—coming as it does from regions where it naturally has less velocity—it does not at once acquire the velocity of the earth’s motion at the equator; and since the rotation of the earth is from west to east, this portion of the water lagging behind forms a stream or current which has an apparent motion from east to west, that is to say, apparent as regards the earth, but real in relation to the adjacent land and water. The trade winds, which in this zone blow constantly in the same direction, lend their aid in maintaining the equatorial current.