Chap. 7. PHILOSOPHICAL DISCOVERIES. 351

CHAP VII.

Of the ebbing and flowing of the sea.

I T is not in the motions of the celestial bodies only, that the' effects of their mutual gravitation are visible, for we arenow to shew, that a phænomenon which pastes on our earth,and is known to every body, proceeds from the fame principle;I mean, the ebbing and flowing of the sea, the solution ofwhich, from the bad success of those who attempted it beforeour author, had become a reproach to philosophy. But hehas very plainly and fully accounted for it, from the unequalgravitations of the parts of the earth towards the fun and moon.It will be worth while, because it is a very celebrated question,to be the more particular in explaining his solution of it.

It is obvious, that, if the earth was entirely fluid, and qui-escent, its particles, by their mutual gravity towards eachother, would form themselves into the figure of an exact sphere.Suppose now, that some power acts on all the particles of thisearth, with an equal force, and in parallel directions, the wholemass will be moved by such a power, but its figure will sufferno alteration by it ; because all the particles being equallymoved by this power, in parallel lines, they will still keep thefame situation with respect to each other, and still form asphere, whose centre will have the fame motion as each par-ticle. For, as a drop of water, while it falls towards theearth, retains its spherical figure ; and, as the situation ofbodies in a ship, that moves with an uniform motion forward,is no way affected by the motion which is common to the ship