The sea horizon and its reflection in running water
Why the eye and the horizon see opposite faces of a wave, so a current cannot mirror the horizon back to you
A leaf of the Treatise on Painting on the sea horizon and reflection in water. A first proof sets the shore at n and the observer's eye height a n, and shows how the world's central line m o meets the visual line a r at the horizon o, the surplus a m over o m equalling the eye-to-foot height. A lettered chapter then argues that running water between eye and horizon cannot reflect the horizon back to the eye, because the eye and the horizon each see the opposite face of a wave, and a further heading opens the case of where the horizon is mirrored on a wave. A circle diagram of the horizon and two lettered wave diagrams accompany the text, along with the running head and a catchword not part of the transcription.
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The sea horizon and the observer's eye height
Let n be the shore and a n the height of the man who sees the maritime horizon at o, where the world's central line m o falls perpendicular on the visual line a r ending at o on the sea surface. The central line a m exceeds the central line o m by the whole excess a n, the distance from the man's feet to his eyes.
Running water cannot reflect the horizon to the eye
Water running between eye and horizon will not reflect that horizon to the eye, because the eye does not see the face of the wave that the horizon sees, nor the horizon the face the eye sees. With wave c b, eye a, and horizon d, the eye, not seeing the sides b g, will not see the reflected image of d that is mirrored on that face.
Two diagrams of a wave and its faces toward eye and horizon
Below the text two small figures show a wave profile with lettered points, one drawn as a rounded crest and one triangulated, marking the faces of the wave that turn respectively toward the eye and toward the horizon in the reflection argument.