Between the oscillating limit of the Zone of Calms and the parallel of 28° in the Northern Hemisphere, on one side of the globe, and between the correspondent limit and the parallel of 25° south latitude, on the opposite hemisphere, there prevail through above two-thirds of the earth’s circumference, steady winds, blowing with almost undeviating uniformity from the eastward. These are the trade-winds. More precisely, _the trade-wind of the Northern Hemisphere is a wind blowing from the northeastward_--that is, a _northeast wind_. _The trade-wind of the Southern Hemisphere blows from the southeastward_, and is _a southeast wind_. The trade-wind belts stretch round more than two-thirds of the earth’s surface. They comprehend (within the latitudinal limits already defined) the Atlantic and Pacific Oceans, with the countries that lie adjacent to those vast areas of water. In the Pacific, however, their limits are less distinctly marked, and their influence less powerful, to the southward of the equator than to the north of that line. Over the Indian Ocean and its shores, the atmospheric currents follow, during portions of the year, an opposite course. The trade-winds of the Atlantic and Pacific--blowing constantly, and with almost undeviating steadiness, from the eastward--regulate the course of the mariner across those oceans. They, of course, facilitate the passage of either ocean in a westerly direction--that is, from the shores of the Old World to the eastern seaboard of America, or from the western coast of the New World to the eastern shores of the Asiatic and Australian Continents. It was the trade-wind of the Northern Atlantic that carried Columbus to the westward, on the adventurous voyage which resulted in the discovery of the New World, inspiring terror in the breasts of his companions, while in the mind of the great navigator himself it strengthened the assurance of reaching land by pursuing the direction in which his vessels’ prows were turned. On a like great occasion, the trade-wind of the Pacific carried Magellan’s ship steadily forward through the ocean which he was the first to cross, and facilitated the earliest circumnavigation of the globe. On the other hand, the same winds compel the return voyage across either ocean to be made in higher latitudes, where westerly winds prevail. The explanation of the trade-winds is found in the different measure in which the sun’s heat is experienced by regions within or nearly adjacent to the tropics, and by those of higher latitudes. They are currents of air set in motion by the differences of density consequent upon such various conditions of temperature--conditions which are of uniform prevalence, and the result of which is also constant.