Notes and Drawings on the Thorax and Abdomen

Conclusion on the impact of air

in the midst of water, or of water within air

Let air be one medium and water the other medium, and let the surface that divides them be flat; and let the impact be made by a stone or other heavy falling body original: "grave cadente" from the air into the water. I say that the motion of the water will not be of a single quality, but will vary according to the variety of the position where the aforementioned heavy body strikes. Because if the heavy body is round and strikes flatly, it will drive the water in every direction equally; and if the heavy body is oblique meaning tilted or striking at an angle, it will drive the water more to one side than the other. And if the heavy body is flat and strikes flatly, it will drive the water in every direction equally; and if the heavy body is oblique, it will drive the water more to the side where it is most inclined.

The air follows the heavy body into the water and then returns to the surface.

Furthermore, the air that is trapped beneath the heavy body at the moment of impact is forced into the water, forming a bubble. This air, being lighter than the water, seeks to return to its own element Leonardo refers to the Aristotelian concept of "natural place," where elements like air naturally rise above denser elements like water. In doing so, it creates a reflux or a counter-motion that disrupts the initial waves caused by the strike.

If the heavy body penetrates deeply, the cavity it leaves behind is instantly filled by the surrounding water. This sudden rush of water toward the center causes a collision of currents, which then results in a vertical spout or column of water rising back into the air.

The height of the spout is proportional to the speed of the falling body.

Thus, we see that the movement of the water is composed of three distinct actions: the initial displacement by the body, the rising of the trapped air, and the collision of the water filling the vacuum. Each of these actions produces its own set of circular waves original: "tremolamenti" on the surface, which intersect and interfere with one another until the equilibrium is restored.