1. _Trade winds._ These are permanent, following the same direction throughout the year. They are met with between the tropics, and a few degrees to the north and south of those limits. The well-known name applied to them is a phrase of doubtful origin, but probably derived from the facilities afforded to trade and commerce by their constant prevalence and generally uniform course, though Hakluyt speaks of the “wind blowing trade,” meaning a regular tread or track. The parallels of 28° north and south latitude mark the medium external limits of the trade winds, between which, with some variations, their direction is from the north-east, north of the equator, and from the south-east, on the other side of the line, hence called the north-east and south-east trades. They are separated from each other by the region of calms, in which a thick foggy air prevails, with frequent sudden and transient rains attended by thunder and lightning. This region, in the Atlantic, extends across the whole ocean from the coasts of Africa to those of America, but its position shifts, being sometimes entirely north of the equator, and but rarely reaching one or two degrees south; and hence it may be considered as belonging to the northern hemisphere. The region also varies in breadth from two and a half to ten degrees, but usually occupies a width of four or five. These variations are dependent upon the position of the sun, which has an influence likewise upon the strength, direction, and situation of the trade winds themselves. When the sun has a northern declination, and approaches the tropic of Cancer, the boundary line of the north-east trade wind extends to 32° north latitude, and the wind has a more easterly direction, but the parallel of 25° is its northern boundary, and the wind inclines more north when the sun is south of the equator, and approaches the tropic of Capricorn. At that season, the southern boundary of the south-east trade wind extends to 30° S. lat., and the whole ocean is swept by it between that line and about 1° N. lat. The general width of the south-east trade is about 9° greater than that of the north-east, the region of calms, as before stated, being almost wholly in the northern hemisphere. In the basin of the Atlantic, the zone of the trade winds becomes broader, and their direction more easterly, as the coast of America is approached, the breezes blowing to the very shore. This is not the case on the African side of the Atlantic, where, through a tract of sea extending from fifty to eighty miles off shore, these winds are not found at all, but contrary westerly breezes prevail. The irregularity is easily explained. Owing to the rarefaction which the air undergoes over the great hot desert of the Sahara, the colder air from the contiguous sea rushes in to supply the partial vacuum created, and keep up the equilibrium of the atmosphere, producing winds blowing toward the shore.