After some wild conjectures of the earliest philosophers, observes Goldsmith, it became well known in the time of Pliny that the tides were entirely under the influence in a small degree of the sun, but in a much greater of the moon. It was found that there was a flux and reflux of the sea in the space of twelve hours and fifty minutes, which is exactly the time of a lunar day. It was observed that whenever the moon was in the meridian, or in other words, as nearly as possible over any part of the sea, that the sea flowed to that part, and made a tide there; on the contrary, it was found that when the moon left the meridian, the sea began to flow back again from whence it came, and there might be said to ebb. Thus far the waters of the sea seemed very regularly to attend the motions of the moon. But as it appeared, likewise, that when the moon was in the opposite meridian, as far off on the other side of the globe, that there was a tide on this side also, so that the moon produced two tides, one by her greatest approach to us, and another by her greatest distance from us; in other words, the moon, in once going round the earth, produced two tides, always at the same time; one, on the part of the globe directly under her; and the other, on the part of the globe directly opposite. Kepler was the first who conjectured that attraction was the principal cause; asserting, that the sphere of the moon’s operation extended to the earth, and drew up its waters. But what Kepler only hinted, has been completely developed and demonstrated by Sir Isaac Newton. After his great discovery of the law of gravitation, he found it an easy matter to account for the whole phenomena of the tides. The moon, like all the rest of the planets, has been found to attract and to be attracted by the earth. This attraction prevails throughout our whole planetary system; the more matter there is contained in any body, the more it attracts, and its influence decreases in proportion as the distance, when squared, increases. This being premised, let us see what must ensue upon supposing the moon in the meridian of any tract of the sea. The surface of the water immediately under the moon, is nearer the moon than any part of the globe is, and, therefore, must be more subject to its attraction than the waters anywhere else. The waters will there be attracted by the moon, and rise in a heap, whose eminence will be the highest where the attraction is greatest. In order to form this eminence, it is obvious that its surface, as well as the depths, will be agitated, and that wherever the water runs from one part, succeeding waters must run to fill up the space it has left. Thus the waters of the sea, running from all parts to attend the motion of the moon, produce the flowing of the tide; and it is high tide at that part wherever the moon comes over it, or to its meridian. {11}