Water as Microscope of Nature

On one of the sheets of the Codex Leicester, Leonardo analyzes fish swimming in order to obtain information that might help humans stay afloat in water and swim. He asks himself how to do a “dead float,” how to avoid being dragged underwater by whirlpools, and how to swim on one’s back. He also mentions his invention for staying underwater for long periods. However, he does not reveal it “because of the evil nature of men,” as they would use it to sink enemy ships, causing the death of their occupants.