ON FORTIFICATION.

Beyond the previously mentioned styles of gates, others have indeed been constructed that open automatically with the receding tide as it falls to the bed, and rise again with the incoming tide; likewise, there are gates that are hoisted sideways within the land, but in practice, they are not found to be so convenient.

Up until now, we have discussed what has been in use for a long time, in order to more clearly present the new invention as follows:

After it was observed that these large, wide miter gates original: "portes poinctues". These are "pointed gates" that meet at an angle (like a V) to better resist the weight of the water. shown in Figures 2 and 3 served very well for draining land and for the passage of ships with upright masts, and that for creating great depth in Harbors, the only thing lacking was a means by which one could conveniently open these gates when the water was at its highest on one side and its lowest on the other, several people occupied themselves very seriously with this problem. This was especially true here in Holland, where in the Cities, Villages, and the open Country, there is such a great quantity of Sluices original: "Escluses". A general term for water control structures, including locks and floodgates.—and so many new ones are continually being built with great care, both at high cost and of more modest size—that I estimate that at present, in all the world, there is no Country with more experience in this matter, nor any where more subtle minds are occupied in seeking and finding improvements for Sluices. By their efforts, the method which I shall describe, and which seems to me the best, has come into use.

To this end, let this 4th Figure represent a sluice with two miter gates of this quality: A B C D is a rectangular frame, in which there is a gate E F G H turning on a pivot original: "esguille". Literally a "needle," here referring to a vertical iron axle or spindle. I K near the middle of the frame, such that the part I F G K is about 5 or 6 fingers An old unit of measure, approximately 3/4 of an inch. wider than the part I E H K (or more or less as the size of the gates might require). Thus, the three sides I E, E H, and H K of the smaller part come to press against the rebates original: "feuillieres ou fillerets". These are the grooves or recessed ledges in the frame that the gate rests against to form a seal. made on the inner side of the frame, but the three sides I F, F G, and G K of the larger part do not rest against the rebates. Consequently, when the high water presses against these two parts, the gate E F G H will turn (because the pressure is greater against the larger part) until it has made about a quarter-turn. But to keep it firm and to open it easily as one desires, this is done with an iron bar which, standing upright like a spindle and being turned, comes before the side F G of the gate, holding it firmly locked.