=Movements generated by winds.=—The circulation resulting from the tendency of the winds to change the level of the sea-water has already been mentioned, but the wind also works in other ways. Where the winds have a somewhat constant direction and are at the same time strong, they determine a general movement of the surface-waters in their own direction, the surface-water being dragged along at a rate somewhat less than that of the wind itself. The constant trades appear to be the chief generators of the equatorial ocean-currents. Once generated, these currents may be concentrated and their courses modified. The currents generated by trades are turned north and south when directed against a continent; they are modified by the configuration of the bottom if the water be shallow, and always and everywhere, except, at the equator, they are deflected by the rotation of the earth, in the northern hemisphere to the right, and in the southern to the left. The pole-ward currents generated in the equatorial region by the trades, and directed by the winds, the lands, the configuration of the bottom, and the rotation of the earth, determine compensating currents from high latitudes to low, and the same influences which control the course of the former direct the latter as well. Since the atmospheric movements are so far constant that there is a prevailing direction of winds in all latitudes, the winds, as well as differences of density and differences of level, insure a general and continual circulation of sea-water. The geological effects of this circulation are direct and indirect; direct, by gradation of the bottom over which they flow, and indirect, by the modifications of climate they produce. Since rotation deflects the pole-ward currents to the east sides of the oceans (west sides of the continents) and the equator-ward movements to the west sides of the oceans (east sides of the continents), the east shores of the oceans are warmer than the west in corresponding latitudes, and the west sides of the continents are both warmer and moister[148] than the east sides. The most obvious disturbance of sea-water resulting from the winds is the generation of _waves_. Waves are not primarily parts of the general oceanic circulation. Since they are generated in other ways than by winds, and since the gradational effects of waves are independent of their origin, the effects of wind-waves will not be considered separately. =Movements generated by attraction.=—One of the movements of the sea-water which is not primarily circulatory results from the attraction of the moon and sun. The tide is really the result of the _inequalities_ of the attraction of these bodies on different parts of the earth. The lunar tide is more important than the solar, not because the attraction of the moon is greater, for it is not, but because its differential attraction, the result of its lesser distance, is greater.