But when the moon travels onward, and ceases to point over the place where the waters were just risen, the cause of their rising ceasing to operate, they will flow back by their natural gravity into the lower parts from whence they had travelled; and this retiring of the waters will form the ebbing of the sea. {12a} Thus the first part of the demonstration is obvious, since in general it requires no great sagacity to conceive that the waters nearest the moon are most attracted or raised highest by the moon. But the other part of the demonstration, namely, how there come to be high tides at the same time on the other side of the globe is not so easy to conceive. To comprehend this, it must be observed, that the part of the earth and its waters farthest from the moon, are the parts of all others that are least attracted by the moon; it must also be observed, that all the waters, when the moon is on the opposite side of the earth, must be attracted in the same direction that the earth itself attracts them; that is apparently quite through the body of the earth, towards the moon itself. This, therefore, being conceived, it is plain that those waters which are farthest from the moon will have less weight than those of any other part on the same side of the globe, because the moon’s attraction, which conspires with the earth’s attraction, is there least. Now, therefore, the waters farthest from the moon having less weight, and being lightest, will be pressed on all sides by those that having more attraction are heavier, and the heavier waters flowing in, will make them swell and rise in an eminence directly opposite to that on the other side of the globe, caused by the more immediate influence of the moon. {12b} In this manner the moon, in one diurnal revolution, produces two tides; one raised immediately under the sphere of its influence, and the other directly opposite to it. As the moon travels, this vast body of waters rears upward, as if to watch its motions, and pursues the same constant rotation. However, in this great work of raising the tides, the sun has no small share, it produces its own tide constantly every day, just as the moon does, but in a much less degree, because the sun is at an immensely greater distance. Thus there are solar tides and lunar tides—when the forces of these two great luminaries concur, which they always do when they are either in the same or in the opposite parts of the heavens, they jointly produce a much greater tide, than when they are so situated in the heavens as each to make peculiar tides of their own; in the former, the attraction of the sun conspires with the attraction of the moon, by which means the high spring tides are formed; in the latter, the action of the sun is opposed to that of the moon, consequently the effect must be to depress the waters where the moon’s action has a tendency to raise them, and hence the production of the lower neap tides. {13a}