eyelid. How false the opinion is of those who say that this happens because the pupil of the eye is displaced from its position.
How the above mentioned facts prove that the pupil acts upside down in seeing.
[Footnote: 82. 14—17. The subject indicated by these two headings is fully discussed in the two chapters that follow them in the original; but it did not seem to me appropriate to include them here.]
Demostration of perspective by means of a vertical glass plane (83-85).
83.
OF THE PLANE OF GLASS.
Perspective is nothing else than seeing place [or objects] behind a plane of glass, quite transparent, on the surface of which the objects behind that glass are to be drawn. These can be traced in pyramids to the point in the eye, and these pyramids are intersected on the glass plane.
84.
Pictorial perspective can never make an