On the Motion and Measurement of Water

LEONARDO DA VINCI 281

CHAPTER XVII.

Of waters joined together, all those that exceed the height of the Ocean will have gravity and will be in natural motion Natural motion, in the physics of Leonardo's time, refers to the movement of an object toward its "natural place"—for heavy things like water, this means moving downward toward the center of the world.. This is proven because all waters situated higher than the surface of the sphere of water Leonardo envisions the Earth as a globe where the water forms a theoretical perfect sphere or "shell" around the center. are more remote from the center of the World In the geocentric cosmology Leonardo studied, the center of the Earth was considered the center of the universe. than that surface; therefore, by the fourth [proposition] they will have gravity and natural motion.

CHAPTER XVIII.

The motions of heavy elements original: "elementi gravi." Specifically earth and water, which were believed to possess an innate desire to move toward the center of the universe. are not toward the center for the sake of reaching that center, but because the medium where they are located cannot resist them; and when the element finds resistance in its own element, its body no longer weighs, nor does it seek any longer to go to the center. Therefore, when water descends, it does not descend to go to the center, but because it finds no resistance in its medium [the air]. Since water weighs in the air, it descends by the shortest path, and divides and opens the air that lies below the center of its gravity with all its parts equally; it does not divide the air that is at its sides, because it is not situated above it. Because of this, a "hole" of the shortest length is made through the air until the water reaches that which resists it. This resistance being water, that water which was falling through the air into this water no longer seeks to go to the center, because it no longer divides the water as it did the air.

CHAPTER XIX.

Naturally, no part of the land uncovered by water will ever be lower than the surface of the sphere of the waters. D B (fig. 9 plate I.) is a plain from which a river flows to the sea; and because in truth this uncovered land is not in a position of equality—since if it were so, the river would have no motion—wherefore this site, being in motion, should rather be called a slope than a plain. And thus this plain D B terminates in such a way with the sphere of the water that if one continues it in a straight line original: "continua rettitudine." from B to A, this A would enter beneath the sea; and from this arises the fact that the sea seems higher than the uncovered land, etc.