NEW METHOD

are about twice as long as those of the 5th Figure, because the angle D E A in the 7th Figure must be very obtuse An angle greater than 90 degrees. to be able to open them; this opening would be impossible if that angle were a right angle. Consequently, these gates are as long as the Sluice is wide—being 30 feet at Schiedam—whereas the needle-supported pivoting gatesoriginal: "Eſcluſes à portes tournantes ſur eſguilles"; a system where gates pivot on vertical beams called "needles." with their frames require only 16 feet each. This great length of the gates causes significant weight, so much so that at Schiedam they are made to run on copper rollers fixed to the lower side of the frames, turning on an iron-plated foundation. Thus, if one wished to make pivoting gates on needles of such length, the Sluice would become about twice as wide. Secondly, the opening of a Sluice which is done by simply lifting a latch original: "loquer"; a locking mechanism or bolt. is more convenient than the other method.

CHAPTER 2.

On the reinforcement of the foundations of Sluices and Dams.

ALTHOUGH the foundations of Sluices and Damsoriginal: "Dodanes ou Retenues"; these refer to water-retaining structures or weirs used to manage water levels in the Low Countries. are constructed in these Lands with great foresight and at great cost, one has nonetheless been unable to achieve such certainty that great inconveniences do not often arise from high waters. By these waters, the foundations are so ruined or undermined that the Sluices become useless, and the Dams fall and sink deep under the water, flooding the Country. But since this happens to Sluices which are not nearly as wide or deep as the proposed needle-sluices—through which the largest Ships would pass—someone might doubt, and not without reason, whether this imperfection of the foundations might ultimately make it impossible to achieve what is expected. But because my opinion is otherwise, I will first describe, in order to clearly explain it, the cause of this imperfection, so that through such knowledge this method of reinforcement might have better success.

For this purpose, let A be the profile of a Dam, B the exterior water, C the interior water or the ditch, and D E the foundation on which the Dam rests. When this exterior water B reaches near the top of the Dam at F, as sometimes happens, there are two principal causes that make it fall: First, the deep rupture which, with such extraordinarily high waters, sometimes occurs at the foot of the Dam where previously there had been none. This rupture, reaching lower than the masonry of the Dam and then beneath the Dam, ruins and scatters the foundation, toppling the Dam. And although such a rupture does not occur when the Dam is placed further back—so far from the mouth of the ditch that the river's flood does not strike against it—there is then, at low water, a stretch of dry ditch from the Dam to the mouth, which is damaging to the City's Fortification. The other cause is the pressure, which with such extraordinarily high water is so extremely strong that the flow of the high water under the Dam from B through D E to the low water C acquires the force to move or shift the sand. Once it has reached this point, this shifting suddenly grows larger and larger, proceeding like a fire in houses, which, starting with a small flame, immediately increases. In such a way, the foundation being scattered, the Dam breaks and sometimes sinks entirely under the water. These two causes happen to some Dams together, which then makes them fall more easily.