HYDRAULIC ARCHITECTURE, BOOK III.

earth. Everything then contributes to diminishing the movement of the sea: not only does it rise less high in this case, it also descends less low, for these two peculiarities always accompany each other, or are, so to speak, inseparable.

The tide of a single day swells more or less according to the diversity of the coasts. Example of what happens on those of Brittany & England.

594. As time is required before the impulse or attraction of the moon & sun is felt in places far from the tropics, the tide of a single day is delayed in proportion to the distance of the place, & swells more or less according to the various positions of the coasts. For example, after striking against the shore of Spain, it slides along that of France, entering the English Channel original: "la Manche", where, finding itself reflected & constricted by the coasts of England & its islands, it produces more considerable effects in certain ports than in others. It is for this reason that one sees the sea rise in spring tides original: "vives eaux"; the highest tides occurring after new and full moons. from 35 up to 45 feet at Saint-Malo, Cancale & Granville; this is because there, the waters find themselves constricted upon entering a sort of gulf. The first waters to reach the back of the irregular recess formed by the coasts of Brittany, being unable to escape for lack of an outlet, rise as they are pushed by those coming after, which are all determined by a movement—either direct or reflected—to advance from the same side; whereas the sea only grows by 9 to 10 feet in neap tides original: "mortes eaux"; the period of the month when the difference between high and low tide is the least.. One may conjecture that this latter occurrence comes from the fact that the volume of water during the quadratures The phases of the moon occurring at the first and third quarters. not being as strong, it passes easily into the channel, & not striking with enough force against England, it consequently cannot reflect toward the bay of Mont Saint-Michel; whereas during the new & full moons, it flows back toward this side & occasions many circulations in these waters, which cause the sea to swell more there.

In the open sea, the waters do not rise as high as toward the coasts. Error of those who claimed that there was no more tide beyond the sixtieth degree of latitude.

595. It happens, on the contrary, that in the open sea & at islands very far from the continent, where the waters cannot push back against one another, they rise only a little. We are assured that even under the torrid zone, where it would seem that the tides should be stronger than anywhere else because the cause acts more immediately, the sea hardly rises more than 3 or 4 feet; however, Bouguer Pierre Bouguer (1698–1758), a French mathematician and hydrographer known for his scientific expedition to Peru to measure the shape of the Earth. observed during his voyage to Peru, made by order of the King, that at Panama, in the South Sea, the tide rose to more than 16 feet. It swells roughly the same along the coasts of Spain, rising to a height of 14 to 15 feet; on those of Brittany 16 to 17; in Normandy, Picardy & Flanders 17 to 18 feet, while in