Membraned water in the air and the persistence of motion in water
Why a jet holds together unlike a thrown stone, and why impressions last longer in water than in air
Leonardo contrasts a continuous water jet with a thrown projectile: water launched into the air follows for a while the line of the openings from which it issues and holds together because of its 'membraning,' whereas a stone hurled by the circling arm follows a straight path as a discontinuous body. A second note argues that motions impressed within water are more lasting than those made in air, because water within water has no weight and only the impetus that moves it weighs, persisting until consumed. Such impressions endure longest where fast water enters a slower pool, and are destroyed at once when water in the air begins its natural fall toward the earth. A spiralling eddy is drawn at the right.
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Why a water jet holds together unlike a thrown stone
Water made to move through the air follows for some space the line of the openings from which it descends, because its membraning binds all its parts together over a long course. A discontinuous body such as a stone thrown by the circling motion of the arm follows instead a straight path.
Water within water does not weigh; only the impetus weighs
The impressions of motions made by water within water last longer than those made in air, because water within water has no weight, as proved in the fifth book. Only the impetus weighs, moving the water without weight until that impetus is consumed.
Impressions of motion last longer in water than in air
Impressions endure longest where water carried by the impetus enters a pool of slower motion, and the reverse holds too. Impressions made in the air are destroyed at the first motion the water makes toward the earth, as the impetus is spent in the water's natural fall.