On the Motion and Measurement of Water

LEONARDO DA VINCI 276

...center of the World In Leonardo's physics, "centro del Mondo" refers to the center of the Earth, which he understood as the center of gravity for the heavy elements., and at the same distance as that particle which is surrounded by it from said center. Therefore, by the third conception referring to a previously established axiom or "common notion" in his scientific method, such a particle of water will not move of its own accord because it is surrounded by banks of equal height, and thus every circle of such particles becomes a vessel for the particle enclosed within that circle, which vessel has the circumference of its lips at equal height. And for this reason, such a particle, together with all other similar ones that compose the surface of the sphere of water, will by necessity be motionless in itself; and consequently, since each is at an equal height from the center of the World, necessity makes that surface spherical. And below, it is not necessary to be spherical, as reason and experience show Leonardo acknowledges that while the surface of the ocean or a lake is curved due to gravity, the seabed or the "bottom" of the water element is irregular..

CHAPTER V.

Another proof that the sphere of water is perfectly round.

Water does not move of its own accord, as was said in the previous [chapter], unless it descends; and if it moves of its own accord, it follows that it is descending. Therefore, no part of the sphere of water is to move of its own accord, and this is because any part is surrounded by water of equal height, which encloses it and cannot be surpassed by it in any direction. Below the proof is shown (fig. 1, plate I.). Let ABH be the sphere of water, let C be a quantity of water surrounded and enclosed by water A and B. I say, by the previous conclusion, that water C will not move because it finds no descent by the definition of a sphere, because parts A and B of the surface of the water are equally remote from the center of the World, just as C is a part of the same surface of the water, and thus it follows that C remains immobile.

CHAPTER VI.

That if the element of water were not spherical, the water would move of its own accord.

Given, for example original: "verbi-grazia"; a Latin-derived phrase meaning "for example" or "for the sake of the word.", a plane of water on the surface of the sphere of water, the extremes will move to the middle of such a plane. This is proven with the figure that follows (fig. 2, plate I.). And let the plane ABC be given in the sphere ACMD: I say that water A and water C will move toward water B. For if water does not move (as was said for the fourth [chapter]) unless it descends; and it does not descend unless it is higher; and that which is further from the center of the World is higher, it follows that the water...