parts where the pressure is greatest, namely, ose where the moon is near the horizon. The which otherwise would be spherical, upon pressure of the moon must form itself into a roidal or oval figure, whose longest diameter here the moon is vertical, and shortest where s in the horizon; and the moon shifting her ion as she turns round our globe once a day, oval of water shifts with her, occasioning by the two floods and ebbs observable in each and twenty hours. The spring-tides upon ew and full moons, and the neap tides upon Quarters, are occasioned by the attractive force e sun in the new and full, conspiring with the ction of the moon, and producing a tide by united forces. Whereas in the quarters the raises the water where the moon depresses, on the contrary; so as the tides are made ony the difference of their attraction. The sun moon being either conjoined or opposite in equinoctial, produce the greatest spring-tides. e subsequent neap-tides being produced by the ical moon in the quarters, are always the least

*S.

But then from the shoalness of the water in maplaces, and from the narrowness of the straits, which the tides are in many places propagated, re arises a mighty diversity, which, without knowledge of the places, cannot be accounted

Dr. Cheyne has taught me to take notice of one ing more. If our earth had any more than one Loon attending it, we should receive probably a etriment from it, rather than an advantage. For it the conjunction and opposition with one anoth

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those parts where the pressure is greatest, namely, in those where the moon is near the horizon. The sca, which otherwise would be spherical, upon the pressure of the moon must form itself into a spheroidal or oval figure, whose longest diameter is where the moon is vertical, and shortest where she is in the horizon; and the moon shifting her position as she turns round our globe once a day, this oval of water shifts with her, occasioning thereby the two floods and ebbs observable in each five and twenty hours. The spring-tides upon the new and full moons, and the neap tides upon the quarters, are occasioned by the attractive force of the sun in the new and full, conspiring with the attraction of the moon, and producing a tide by their united forces. Whereas in the quarters the sun raises the water where the moon depresses, and on the contrary; so as the tides are made only by the difference of their attraction. The sun and moon being either conjoined or opposite in the equinoctial, produce the greatest spring-tides. The subsequent neap-tides being produced by the tropical moon in the quarters, are always the least tides.

But then from the shoalness of the water in many places, and from the narrowness of the straits, by which the tides are in many places propagated, there arises a mighty diversity, which, without the knowledge of the places, cannot be accounted for.

Dr. Cheyne has taught me to take notice of one thing more. If our earth had any more than one moon attending it, we should receive probably a detriment from it, rather than an advantage. For at the conjunction and opposition with one anoth

what the original of it? Where is the zaphnath paaneah who shall enlighten us?

On our globe all bodies have a tendency towards the centre of it. And such a gravitation there is towards the centre of the sun, and of the moon, and of all the planets. There is cause to suspect that the force of gravity is, in the celestial globes, proportional to the quantity of matter in each of them. The sun, for instance, being more than ten thousand times as big as the earth, its gravitation, and the attracting force of it, is ten thousand times as much as that of the earth, acting on bodies at the same distances.

If our globe were alone, or not affected by the actions of the sun and the moon, the ocean, equally pressed by the force of gravity towards the centre, would continue in a perfect stagnation, always at the same height, without ever ebbing or flowing. But it is demonstrated, that the sun and the moon have a like principle of gravitation towards their centres, and our globe is also within the activity of their attractions. Whence it will follow, that the equality of the pressure of gravity towards the centre will be thereby disturbed. And though the smallness of these forces, in respect of the gravitation towards the centre of the earth, render them imperceptible, yet the ocean being fluid, and yielding to the least force, by its rising shews where there is the least pressure upon it, and where it is most pressed, by sinking. Accordingly we shall find, that where the moon is perpendicularly either above or below the horizon, there the force of gravity is most of all diminished, and consequently that there the ocean must necessarily swell, by the coming in of the water from