Hydraulic Architecture, Volume 2, Part 2

HYDRAULIC ARCHITECTURE, BOOK III.

...to compose the book Knowledge of the Times original: "connoissance des tems"; this was the first national ephemeris (a set of tables providing the positions of celestial bodies), published annually by the French Academy of Sciences since 1679. which the Academy of Sciences publishes every year, did not mark with enough precision some phase of the moon—whether they had fallen into some error of calculation, or whether it came from some printing errors—and what is worthy of remark is that if it was known in Paris that a mistake had been made, it was only learned through those who observed the moment of the ebb and flow in the seaports. These observers noticed that some tides did not agree as usual with the combined movements of the sun and the moon, or simply with the phases of the second of these planets.

It seems astonishing that despite the great distance between our coasts and the place where the cause of the tides acts, the flow takes so little time to reach them; however, one will cease to be surprised when one reflects that the continuity of the parts of the water means that those which have received the first impression communicate it to the nearest parts, these to others, and so on successively.

Hypothesis of Mr. Descartes who attributes the flow to the pressure the moon can cause, from which he deduces why this movement of the sea happens at the same time on two diametrically opposite points of the earth.

588. We are not undertaking to discuss whether the sun and the moon act upon the sea by way of pressure, as Mr. Descartes thought, or if it is by attraction, as Mr. Newton claims. The former supposes that the earth is enveloped by a torrent of ethereal or subtle matter, which forms a vortex original: "tourbillon"; Descartes' theory of physics suggested that celestial bodies were carried by "whirlpools" of invisible matter. whose limits extend beyond the moon. In this case, the matter of the vortex, circulating faster near the earth than it does higher up, is obliged to pass under the moon, where, finding itself squeezed between the underside of this planet and the surface of the earth, it will act upon the Ocean and force its waters to flow back all around, which forms the flood-tide in our ports. But as the earth continues its movement and no longer presents the same faces, the pressure ceases because the waters that had moved away from the tropics return to occupy the space they had abandoned. In this regard, it must be noted that this kind of perpetual balancing must happen at the same time on the two diametrically opposite points of the earth, if there are waters there. Indeed, swimming in a fluid, its place is only determined by the equality of the impulses of the matter surrounding it; consequently, the part corresponding to the moon cannot be more pressed than the others without the earth recoiling ever so slightly, advancing toward the opposite part, which finds itself by this action just as compressed by the matter against...

Academy of Sciences, ebb and flow, tides, Descartes, Newton, vortex, ethereal matter, Ocean, tropics