Why Two Eyes See Light More Strongly Than One
Optical experiments on brightness and the number of eyes, a breaking wave, and a maxim on Aristotle and Alexander
Optical notes crowd the page around three small diagrams: bright-and-dark objects, an eye-and-rays figure, and a red-chalk sketch of a breaking wave. Leonardo argues that two eyes perceive light more strongly than one, since the strip of air seen by both eyes (c d) is judged twice as bright as the strip seen by a single eye, and that the same tone looks different to different eyes. A separate passage describes how a wave rolls back on itself, tumbles as it strikes the shore, and collides with the next wave. At the head stands a maxim pairing Aristotle and Alexander as men who each usurped their domain, the world and the sciences.
On this page
Two eyes deliver a stronger splendour than one
Eye b sees all the air c e and eye a all the air c d; the strip c d, being seen by both eyes, is judged twice as bright as the strip d e that only eye b sees. Two eyes thus give a doubly powerful splendour to the single perceptive faculty than one eye can.
The same tone looks different to different eyes
One and the same whiteness or darkness will appear of as many degrees of brightness or darkness as there are different eyes that view it. Shut one eye and the thing seen by the other looks darker than it did with both eyes open.
How a breaking wave rolls back and meets the next
The wave turns back on itself and rides up, then, striking the shore, makes its tumble and drops below, colliding afresh with the following wave that comes beneath, striking it from below and rolling it back again, and so on in succession.
Aristotle and Alexander, each a usurper
Aristotle and Alexander were preceptors of one another. Alexander was rich in dominion, which was his means to usurp the world; Aristotle had great science, which was his means to usurp all the rest of the sciences assembled by the whole body of philosophers.