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may be transported, by winds and currents, to an enormous distance from their point of origin, before being deposited upon the bottom.
Among the islands of the South Sea, the channels, as between islands, are free and clear, and carry deep, navigable waters, with probably few sunken rocks to interfere with navigation. The currents flow through some of these channels, varying with the localities, at the rates of ten, fifteen, twenty-one and thirty miles a day. For this reason, it is deemed best to lay well off from shore, when not in a good harbor, of atoll lagoon, or bay. Many vessels have been lost in the sweep of these island currents, dragging their anchors (where anchorage can be had, as very often deep water makes up to almost the reef-line), and drifting in on the breakers, completely at the mercy of the waves. This . often happens, too, m perfectly clear weather, when there is no wind to aid the luckless navigator in "clawing off shore." The main currents, spoken of, have considerable depth, while in others their movements may be termed surface, and sometimes greatly influenced by winds and storms. Others may be termed deep sea currents, whose flow traverses the depths below. These are just as variable as the surface movements. Any bulky article, like a keg, weighted to sink to the depth desired, and with sounding-line and buoy attached, may sometimes be seen, carrying the buoy against the wind and surface current, at the rate of two miles an hour.
It will be readily seen that the course and speed of surface currents can be traced with greater facility than those flowing deep down in the sea. Although the custom is not general, still .in the cause of science it should be so, that in all sea voyages, buoys or bottles, with complete data of time and place, should be cast adrift at least once a week during the voyage.
The data contained in bottle or buoy should, of course, contain the request to note time and place when recovered from the ocean. If this were a general practice among our mariners, the little messengers would be looked for with special interest. The valuable practical data coming from this little source alone would add greatly in helping to perfect current charts of the different oceans.
In view of the varying ocean streams, more particularly among the islands of the South Sea, should development and commerce go hand in hand, the idea of using auxiliary steam-power on all vessels engaged in this particular trade, should meet with some encouragement from the mercantile world. A great deal of time lost in the calms and currents of these regions might be saved, as well as certain protection from storms and adverse currents. In regions where the atolls are, only those experienced in navigating among them, can judge of the value steam-power would have, if only applied for a few hours. The lagoons of the atolls are always safe harboring, but how to reach them with a sailing-vessel in a dead calm, through narrow entrances, and with storms and currents threatening, with the sea breaking over the coral reefs on either hand, is still a problem for the sailor. The same difficulty, if we leave out the sudden gale and currents, presents itself in getting out. Even if the auxiliary were not made a part of the vessel, still a steam-launch of considerable capacity could be carried, to be used only when required. This, I am sure, would obviate many of the difhculties sailing-vessels have to encounter, when trading among the Pacific Islands.
The influence of the tides, mainly caused by the attractive force of the moon and the centrifugal force exercised by the earth's revolutions, no doubt affect the ocean currents considerably. Their rise and fall, ranging in some places from but a few inches to seventy feet, raising and lowering the ocean level alternately, create a variable system of currents too well understood by navigators to require an elaborate explanation here. If we admit, for- example, that while we have a high tide on the one side of the earth, caused by the moon's attraction, and that directly opposite on the other side of the globe there is a high tide, the effect of the centrifugal force of the earth's revolutions, with the consequent depression of the water levels between these points, we have a simple explanation of high and low tides. These points are continually shifting, moving around the earth's watery surface, as the influences causing them move, and explain in a general way, if we leave out local influences, the world's tidal system.
The influence of the heat emitted from the great fire-belt nearly outlining the western hemisphere may have had considerable influence on the ocean currents of the Pacific. At a much earlier period in the world's slow geological processes, when its shell was many miles thinner, it is obvious that the heat from subterranean fires would be more readily imparted to the water, causing a flow of the colder portions towards the points where it had been expanded or driven away by the heat (much as we see the movements of the mobile element when heating it in a vessel over a fire). The impetus given in this manner to the ocean's