Why only nearby waves reflect the sun's image to the eye
The angle of incidence on wave surfaces and on a cylinder; the sun's image on water
The page defines why water waves far from the eye fail to return the sun's image while nearer ones do: only where the geometry of reflection sends the reflected ray to the eye does the image appear. Leonardo notes that wherever the sun sees the water, the water sees the sun and can return its image from every part. He analyses the angle of incidence and its axis on a curved, columnar surface, comparing four angles and showing which pairs are equal because their curved sides share the same curvature. Diagrams of waves and a cylinder struck by the sun's rays, with lettered ray-paths, accompany the reasoning.
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The sun's image returned only by favourably angled waves
Leonardo gives the definition of why waves far from the convergence of rays reflected to the eye by nearer waves do not return the image of the sun that lights them. Wherever the sun sees the water, the water sees the sun and can render its image from every part.
Equal angles of incidence and reflection on a columnar surface
Taking the angle of incidence o n p with axis m n, Leonardo sets down four example angles. Angle o d n equals its counterpart m n c because each has one curved and one straight side, and the curves d n and c n are of equal curvature on a cylinder of uniform thickness; but m n b is smaller than its counterpart m n a.
Reflection from the moving surface of waves
In the wave diagram the incident ray of the sun d and the reflected ray to the eye e are traced through a central line b and lettered points. The axis of the angle of incidence always terminates among infinite equal angles, each equal to its corresponding one.