It is to these inequalities at the bottom of the sea, we must attribute the origin of currents, for if the bottom was equal and level, there would be no other current than the general motion from east to west, and a few others which might be caused by the action of the winds; but a certain proof that most currents are produced by the flux and reflux, and directed by the inequalities at the bottom of the sea, is, that they regularly follow the tides, and change their direction at each ebb and flow. See Pietra della Valle on the subject of the currents of the gulph of Cambay, and the accounts of all navigators, who unanimously assert that in those parts where the flux and reflux of the sea is the most violent, the currents are also most rapid. Therefore it cannot be doubted but that the tides produce currents whose direction always answers that of the opposite hills and all mountains between which they flow. Currents produced by winds, also follow the direction of those hills which are under the water, seldom running opposite to the wind which produces them, any more than those which are occasioned by the tides follow the direction of their original cause. To give a clear idea of the productions of currents, we shall first observe they are to be met with in every sea; that some are rapid, and others slow; that some are of great extent, both in length and breadth, and others short and narrow; that the same cause, whether the wind or tides, which produces these currents, frequently gives to each of them a velocity and direction very different; that a north wind, for example, which should give the water one general motion towards the south, on the contrary, produces a number of currents, separated from each other, and very different both in extent and direction; some flowing towards the south, others south-east, and others south-west; some are very rapid, others slow; some long and broad, others short and narrow; in fact, their motions are so various that we have no idea left of their original cause. When a contrary wind succeeds, all these currents take an opposite course, and follow in a contrary direction, precisely in the same manner as would be the case upon land between two opposite and adjacent hills, provided it was covered with water, as is seen at the Maldiva and all the islands of the Indian seas, where the currents run, and the winds blow, for six months in a contrary direction. The same remark has been made on currents between shoals and sandbanks. In general all currents, whether caused by the motion of flux or reflux, or the action by the wind; have the same extent and direction throughout their whole course, yet differ from each other in most respects, which can proceed only from the inequalities of the hills, mountains, and vallies, at the bottom of the sea, it being certain that the current between two islands follows the direction of the coasts; and the same is observable between banks of sand, shoals, &c.