The nature of mirrors and the reflection of visual rays
Images appear reversed; a ray returns on itself only at right angles
The verso (98v) sets out the science of mirrors: it is their nature to send forth the pyramids of the quality they receive, and if all points of an object are gathered into a single point of the mirror the near eye can grasp the object's form. A numbered marginal list adds that water and mirror surfaces are seen by all they reflect, that every point shows both part and whole, that bodies appear upside down, and that each ray returns upon itself when the object stands in straight opposition. The recto (103r) carries further canceled propositions on the pyramids of visual likenesses and on rays returning only when they strike between right angles. Text in another hand in the upper half of 103r was omitted from the critical transcription.
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Mirrors send forth the pyramids of images they receive
It is the nature of mirrors to send forth from themselves the pyramids of the quality that they receive. The reflected likeness leaves the surface as a cone of rays.
An eye near a mirror grasps the object's whole form
If all the points of the object are contained in a single point of the mirror, the eye being near to it will be able from there to comprehend the form of the object.
Water and mirror surfaces reflect part and whole; images reverse
All things that see the surface of water and of mirrors are seen by those surfaces, and at every point appear both the part and the whole of the bodies. All bodies seen in mirrors appear upside down, and nothing is seen unless it makes an equal proportion of pyramid; a ray from an object in straight opposition returns upon itself to the place of its origin, as shown in the mirrored eye.
Pyramids of likeness joined apex to apex without interval
Universally all the points that cause the extreme tips of the pyramidal likenesses are continued entirely together, joined at their apexes without any interval. A pyramid departing from its base with more unequal, misshapen angles is more slender and a more deceptive shower of the true breadth of its base.
A ray returns to its origin only when it strikes at right angles
No ray, after striking upon the mirror, can return to the place of its origin unless it falls between right angles. Every ray broken upon each point of the mirror generates infinite ones.