variety of uses derived from a single principle is a constant, and a most admirable, characteristic of nature. The primary purpose of the ocean is probably, to supply the land with the moisture necessary to production. But, the collateral effects of the mighty reservoir are felt in results of the first importance, yet of a wholly distinct order. The ocean refreshes the atmosphere, to a certain degree renews its motion, and obviously exerts a powerful agency in preventing alike excessive heat and excessive cold. The tides, which prevent its stagnation – a stagnation which would cover the earth with pestilence – also largely assist navigation in the estuaries, in the lower parts of the great rivers, and in all approaches to the shore. The currents, a portion of this great agency, (still perhaps to give us new sources of wonder,) fulfil at least the triple office of agitating the mass of ocean, of speeding navigation, and of equalising or softening the temperature of the shores along which they pass, in all directions. They seem equivalent to the system of high-roads and cross roads in a great country. It had been said of rivers, that "they are roads which travel;" but their difficulty is, that they travel only one way. The currents of the ocean obviate the difficulty, by travelling all ways. And, perhaps, we may look forward to a time when, by the command of wind and wave given by the steamboat, and by our increased knowledge of "ocean topography," if we may use the phrase; a ship may make its way across the ocean without ever being out of a current; a result which would be obviously a most important accession, if not to the speed, at least to the security of navigation.
Those ocean traversers evidently belong to a system. Some are permanent, some are periodical, and some are casual. The permanent arise chiefly from the effect of the flow from the poles to the equator. Descending from the poles in the first instance, they pour north and south. They gradually feel the earth's rotation; but on their arrival at the tropics, being still inferior in velocity to the equatorial sea, they seem to roll backwards; in other words, they form a current from east to west. This current is farther impelled by the trade-winds.
The progress of this great perpetual current includes almost every part of the ocean. In going westward, it necessarily rushes against the coast of America, where it divides into two vast branches, one running south with great force, and the other north-west. A succession of currents, all connected, obviously form a "moving power" to prevent the stagnation of the ocean, and, by their branches, visit every shore of the globe.
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