Page:Popular Science Monthly Volume 12.djvu/242

230 the point C, the centre of gravity between herself and the moon, is only about sixty-five miles an hour; while the surface at B (Fig. 2) moves with a velocity of 68,000 miles an hour around the sun. Nevertheless, as the waters are driven toward these respective tangents by the effect of centrifugal force, the tide-wave must be greatest where the distance between tangent and curve is the greater.

Let us now proceed to prove by mathematical demonstration the falsity of the theory of the tides found in our text-books. Herschel, in his "Outlines of Astronomy," uses the following language: "That the sun, or moon, should by its attractions heap up the waters of the ocean under it seems to them (objectors) very natural. That it should at the same time heap them up on the opposite side seems, on the contrary, palpably absurd. The error of this class of objectors. . . . consists in disregarding the attraction of the disturbing body on the mass of the earth, and looking on it as wholly effective on the superficial water. Were the earth, indeed, absolutely fixed, held in its place by an external force, and the water left free to move, no doubt the effect of the disturbing power would be to produce a single accumulation vertically under the disturbing body. But it is not by its whole attration,attraction, [sic] but by the difference of its attractions on the superficial water at both sides, and on the central mass, that the waters are raised; just as in the theory of the moon the difference of the sun's attractions on the moon and on the earth (regarded as