a frame of timber, stone, or other matter, serving to retain and raise the water of a river, &c., and on occasion to let it pass.

Such is the sluice of a mill, which stops and collects the water of a rivulet, &c., to let it fall at length in the greater plenty upon the mill-wheel: such also are those used as vents or drains to discharge water off land. And such are the sluices of Flanders, &c., which serve to prevent the waters of the sea from overflowing the lower lands.

Sometimes there is a kind of canal inclosed between two gates or sluices, in artificial navigations, to save the water, and render the passage of boats equally easy and safe, upwards and downwards; as in the sluices of Briare in France, which are a kind of massive walls built parallel to each other, at the distance of 20 or 24 feet, closed with strong gates at each end, between which is a kind of canal or chamber, considerably longer than broad; wherein a vessel being inclosed, the water is let out at the first gate, by which the vessel is raised 15 or 16 feet, and passed out of this canal into another much higher. By such means a boat is conveyed out of the Loire into the Seine, though the ground between them rise above 150 feet higher than either of those rivers.

Sluices are made different ways, according to the use for which they are intended: when they serve for navigation, they are shut with two gates, presenting an angle towards the stream; when they are made near the sea, two pair of gates are made, the one to keep the water out and the other in, as occasion requires; in this case, the gates towards the sea present an angle that way, and the others the contrary way; and the space inclosed by those gates is called the chamber. When sluices are made in the ditches of a fortress, to keep up the water in some parts, instead of gates, shutters are made so as to slide up and down in grooves; and when they are made to raise an inundation, they are then shut by means of square timbers let down in cullyes, so as to lie close and firm.

The word sluice is formed of the French eclusé, which Menage derives from the Latin excluda, found in the Salic law in the same sense. But this is to be restrained to the sluices of mills, &c., for as to those serving to raise vessels, they were wholly unknown to the ancients.