The Eye: Unequal Visual Power and the Convex Pupil
Why the visual faculty is strongest at its centre and why the pupil is convex
This opening page of the notebook argues that Nature gave the eye's visual faculty greater power the nearer it lies to its centre, following the same law by which weights on a balance, columns, walls and even heat grow stronger toward their centre. Leonardo then explains that the surface of the eye was made convex, raised like part of a ball, so that surrounding objects can impress their likenesses at wider angles than a flat eye would allow. A double diagram in the upper-right margin illustrates the greater or lesser convexity of the eye.
On this page
Visual power is greatest nearest the centre
Leonardo holds that the visual faculty is not of equal power everywhere, but is stronger the closer it approaches its centre, so as not to break the law common to all natural powers. He supports this with the act of percussion of a body and with the arms of a balance, where a weight drawn nearer the centre loses gravity, and cites columns, walls, pillars and heat as further cases.
Why the pupil is made convex
Nature made the surface of the light set in the eye of convex figure, raised like part of a ball. This lets the surrounding things impress their likenesses with larger angles, which could not happen if the eye were flat.
Double diagram of the eye's convexity
In the right margin a paired diagram shows a circle with converging lines above and a smaller circle below, illustrating the greater or lesser convexity of the eye's surface. It corresponds to the caption for the double diagram of convexity.