On the Motion and Measurement of Water (1828) - Page 22

LEONARDO DA VINCI 277

...A, and the water C, which are further from the center D than is the water B—which is closer to center D—are higher than water B; for this reason they descend, and for this reason they move toward water B.

CHAPTER VII.

That a spherical heavy body placed upon the sphere of water is motionless.

A spherical heavy body grave sferico: a solid, heavy sphere used as a theoretical weight in physics experiments placed upon the sphere of water will not change its position. The truth of this proposition is manifest through the fourth and fifth [propositions] of this work. Because if the water is spherical—since it cannot move of its own accord within its own sphere, as its parts are equally distant from the center—it follows by necessity that the spherical heavy body, placed in any part of the sphere of water, cannot move; this is because, regardless of where it is placed, it is equally distant from the center of the World original: "centro del Mondo"; in Leonardo's cosmology, the center of the Earth is the center of gravity for the universe. Let ABCN, then, be the sphere of water (fig. 3, plate I); let A be the spherical heavy body, and let N be the center. I say that A will not move toward point B, nor toward point C, because point A is at an equal distance from the center N as are point B and point C.

CHAPTER VIII.

Whether a spherical heavy body placed at the edge of a plane of water will move?

A spherical heavy body placed at the edge of a perfect plane In this context, a "perfect plane" refers to a flat, straight surface. Leonardo argues that on a round Earth, a "flat" surface is actually higher at its edges than at its center of water will not remain still, but will move immediately to the middle of that plane. This is proven by the sixth [proposition]; for if a flat plane of water were placed on the curved surface of the sphere of water, the edges would move toward the middle of such a plane, because the middle is lower closer to the Earth's center than the edges. Therefore, we conclude that the same will happen to a spherical heavy body placed at the edge of the plane of water, because the edge of such a plane is higher than the middle. As appears in the following figure (fig. 4, plate I), where A is a spherical heavy body placed at the edge A of the plane ABC of the sphere ACMD; because it is higher—that is, more distant from the center D—than is point B, which is closer to the same center, it is a necessity that it moves toward point B.