The Lower Eye, the Visual Angle, and Reflections in Water
Air thickness and the low eye; why species converge to one point; images mirrored in clear, turbid and running water
The mountain demonstration closes: the lower the eye n, the thicker the air along the visual line p n, so the base's colour departs further from its natural hue than in the first figure, the same holding for the summits. A geometric section explains why all species converge to a single point: equal magnitudes b d and c e are seen under smaller angles the more remote they lie from the eye a, as the diagram's angle c a e shows against b a d. Three short precepts then treat reflections, noting that clearer water mirrors an object's true colour, turbid water lends the colour that clouds it, and running water lengthens and confuses the image.
On this page
The lower the eye, the more a mountain's base loses its colour
With the eye set lower at n and the mountain's summit and base o p, the visual line p n runs lower than d a of the first figure through thicker air. The base's colour therefore departs further from its natural colour than in the first demonstration, and the same is understood of the summits.
Why equal magnitudes converge to a single point in the eye
Of things of equal size at various distances, the more remote is seen under a smaller angle. Though b d equals c e, c e reaches the eye under a smaller angle the more remote it is from the point a, as the angle c a e shows against the angle b a d.
Objects mirrored in clear versus turbid water
A thing mirrored in water keeps a colour truest to itself when the water is clearer. In turbid water the reflection always takes on the colour of whatever clouds that water.
Objects mirrored in running water
In running water the simulacrum of the object shows itself longer and with more confused edges, the passage opening the discussion continued on the following page.