Hydraulic Architecture, Volume 2, Part 2

CHAPTER I. ON THE FLOW AND EBB OF THE SEA.

...on which it rests, just as the upper part is pressed by the air that weighs upon it.

589. Mr. Newton, on the contrary, claims that all parts of the matter composing the solar system weigh toward one another according to their mass, and in inverse proportion to the square of their distance; and he subjects them all to a universal gravity Newton’s law of universal gravitation, published in 1687, was still competing with Cartesian "vortex" theory in France during the mid-18th century. which he makes reciprocal. Thus, he maintains that the sea rises under the moon and under the sun when they pass through the meridian corresponding to the middle of the ocean, because, according to him, everything here below has some degree of weight toward these two celestial bodies, and at the same time our tendency toward the moon is always much stronger; for though this planet is very small, we are, in compensation, at a very short distance from it.

To make this hypothesis understandable to those who are only moderately versed in physics, let us suppose that T represents the earth surrounded by water, and that B marks the moon; then it will happen, as we have just explained, that part C of the ocean, to which this planet corresponds perpendicularly, will be more attracted by it than all the other more distant parts. On the contrary, the water at G, being then at the greatest distance from the moon, will be less attracted than all the rest included in the hemisphere EGF; thus, becoming lighter than it was Bélidor uses "lighter" to describe the water's relative weight when the gravitational pull on the water is less than the pull on the Earth's center, resulting in the "far-side" tidal bulge., it will also swell further; from which it results that all these waters together will form a kind of spheroid A sphere-like shape that is elongated or flattened; in this case, shaped like an oval or a rugby ball. which has CG for its major diameter and EF for its minor.

Now, as the tides at C and at G, diametrically opposite, both occur at the same time, it is evident that by following the daily revolution of the moon, they must succeed one another alternately under each meridian at intervals of 12 hours and 24 minutes; consequently, they occur twice in a day, because in 12 hours and 24 minutes the moon passes from B to H, where it produces the same effects at G that it had caused at C.

One sees that these two philosophers are diametrically opposed in their explanation, since the first René Descartes maintains that the ocean lowers or forms a hollow under these two planets, at precisely the same time that the second Isaac Newton claims that the sea rises and forms a kind of swelling through its greater convexity; but both equally agree, despite their...