One object seen twice, in two places at the same time
Upper and lower pupil project object c to sites d and g through a hole
A pinhole-vision diagram (an eye at left labelled a and b, a pierced card at centre, and the wall at right marked f and g) supports the proposition that a single pupil can see one object twice, in two places, at the same moment. The lower part b of the pupil sees object c occupy position d, while the upper part a of the same pupil sees the same object c on the wall g f, outside the aperture, at site g. Leonardo concludes that object c is therefore seen at one and the same time in both d and g, and adds that this is what he wished to demonstrate.
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One object seen twice, in two places at once
The opening proposition states that one and the same pupil can see a single object twice, and in two places, at one and the same time.
Upper and lower pupil split object c to d and g (labels f d c a, g e b)
The lower part b of the pupil a b sees object c occupy the site d, while the upper part a sees the same object c on the wall g f, outside the aperture, at the site g. Hence object c is seen at one and the same time in d and g, which is the thing to be demonstrated.