Let it be hypothesized that straight lines drawn out from the eye travel a distance of large magnitudes,
and that the figure enclosed by the sight-lines is a cone having its vertex at the eye and its base at the limits of the things seen,
and that these are seen where the sight-lines fall, and are not seen where the sight-lines do not fall,
and that things seen by a larger angle appear larger, while things seen by a smaller angle appear smaller, and things seen by equal angles seem equal,
and that things seen by higher rays appear higher, while things seen by lower appear lower,
and similarly that things seen by rays more to the right appear more to the right, while those that appear by rays more to the left appear more to the left, and those by more angles appear more precise.
8. Equal and parallel magnitudes at an unequal distance from the eye are not seen proportionally to the distances.
47. There are certain locations, such that when the eye is place at them unequal magnitudes put together at the same point will appear equal to each of the unequal lines.