The nature of mirrors: rays and pyramids of species
How water and mirror surfaces reflect the rays of bodies set before them
This opening gathers Leonardo's optics of mirrors and reflecting surfaces. He writes that it is the nature of mirrors to send back the 'pyramids' of the species they receive, that the surfaces of water and mirrors show the part and the whole of the bodies facing them (which appear upside down), and that a ray meeting a mirror at right angles returns upon itself to its point of origin, as seen in the reflected eye. Many of the lines are struck through, and further text in another hand on folio 103r was omitted from the critical transcription. Both leaves carry figures with letters and sketches of radiating lines and pyramids of rays that the transcription leaves unlettered.
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Mirrors return the pyramids of species they receive
Leonardo states that it is the nature of mirrors to send out from themselves the pyramids of the quality (species) that they receive. This opens the sheet's study of how reflecting surfaces return the images cast upon them.
The eye gathering an object's form at one point of the mirror
If all the points of the object are gathered into a single point of the mirror, then the eye, being near to that point, can comprehend from there the form of the object.
Water and mirror surfaces show bodies inverted
All things that face the surface of water and of mirrors are seen by those surfaces, and at every point of the surface both the part and the whole of the bodies appear, but upside down. Nothing can be seen there unless it makes an equal proportion of pyramid.
A ray at right angles returns to its origin
No ray, after striking the mirror, can return to the place of its origin unless it falls between right angles. And every ray broken upon each point of the mirror generates infinite rays.
Slender pyramids misreport the breadth of their base
The points forming the extreme tips of the pyramidal species are continuous, joined at their apexes without any interval. The pyramid that leaves its base with more unequal and misshapen angles is more slender, and a more deceptive indicator of the true breadth of its base.