1911 Encyclopædia Britannica/Trade Winds
TRADE WINDS, the name given to the winds which blow from the tropical belts of high pressure towards the equatorial belt of low pressure, from the north-east in the northern hemisphere and from the south-east in the southern. They are exceedingly regular, especially over the oceans, where there is no disturbing influence from the great land masses. They receive their name from this feature, the term “trade” being used in the otherwise obsolete sense of “direction” or “course” (cf. “tread”). The area of their greatest influence may be taken to extend from about 3° to 35° N., and from the equator to 28° S., though these belts are actually somewhat narrower at any given season, as the whole system of surface winds over the globe moves north and south following the sun. The westerly winds prevalent in the belts respectively north of the northern tropical belt of high pressure, and south of the southern, are sometimes known as anti-trades, their direction being opposite to that of the trade winds.