Why aligned mountain peaks cannot be told apart by the eye
Peaks a, b, c, d beyond the first mountain merge on its summit when the eye is level with them
Continuing the argument that summits look darker than bases, this page reasons that mountains equally spaced (a, o, p, q) do not keep their colors in the same proportion as their distances, because equal color-proportion would require equal height. When the eye sits at the level of the peaks, every mountain beyond the first rises to the same apparent height, so all their summits coincide on the summit of the first mountain and only that first peak can be seen. Leonardo labels the eye a, the first summit b, and the other peaks c and d, and calls such a demonstration vain. Two small mountain-profile diagrams with ruled sight-lines are inset in the text.
On this page
Equal mountain intervals do not yield equal proportions of color
Although the intervals of the mountains a, o, p, q are equal among themselves, the colors of the peaks o, p, q do not keep the same proportion in their lightening as they would if the peaks were of the same height. Equal height would put their summits in air of equal thickness, making the proportion of distances and of colors one and the same.
Peaks beyond the first mountain coincide on its summit (labels a, b, c, d)
If the eye is as high as the mountain peaks, the peaks of all mountains beyond the first lie at the height of the eye and of the first mountain, so none exceeds or is exceeded by the first. On the surface of the first summit the peaks of all following mountains coincide, and only the first can be seen: a is the eye, b the summit of the first mountain, c and d the other peaks.
Two inset mountain-profile diagrams with sight-lines
Two small drawings of mountain ranges seen in profile are set into the running text, each with a horizontal base line and ruled lines running from an eye toward the successive peaks. They illustrate how, from a low sightline, the further summits fall behind and merge with the nearest one.