Complete Works, Volume Three

of Sections, Parts, and Books,

as they appear with the demonstrations of optics. page 448
2. The first point concerns the cause given in article 12: why do near objects appear more distinct and larger, while distant ones appear more blurred and smaller? Specifically, it is because more rays pass through the pupil and a larger image is depicted on the back of the eye original: "oculi fundo", referring to the retina. same page.
3. Luminous and visible rays (the components from which a visual form or image is made) are the same. In either case, more of them fall upon the eye from a near object than from a distant one. 449
4. A visible object, in relation to the space surrounding it, spreads rays like a center toward a circumference; in relation to the eye, it acts like a circumference toward a center. same page.
5. The diffusion of an object's rays, insofar as they are luminous, is as from a center toward a larger illuminated area, and as from a circumference toward a smaller one. However, insofar as they are visible, it is as from a circumference relative to a single eye, and as from a center relative to many eyes all around. 450
6. It is shown that more rays (naturally, from more parts of the object) strike and meet in the eye when the object is near than when it is far. The rays proceeding from any object are not infinite. A sharper angle also consists of fewer rays. same page.
7. The surface assumed by the famous Ismaël Boulliau Ismaël Boulliau was a prominent French astronomer and mathematician, a contemporary of Gassendi should not be conceived as perfectly polished. The points designated upon it are not to be taken as mathematical points, but as physical ones, like half-spheres or small bumps. 451
8. From each of these half-spheres, various rays go out directly. Because of their radial spreading, or their circular distribution, they cannot all fall into the same eye. 452
9. The small surface of each half-sphere is made rough by many even smaller parts. If their diameters or cords subtensae: the straight lines connecting the ends of an arc, which face toward a nearer eye, are combined into one, they will show a larger total than the combination of those facing a more distant eye. same page.
10. One does not see more in one view than in another (due to a notable compensation), even if, as already said, you look now at the sky, now at a room, or into the palm of a hand. This is because there are indeed smaller and fewer things in a small hemisphere, yet as many rays from them reach the eye as from the larger or more numerous things in a large one. This is argued from flat mirrors and the foreshortening of perspective. 453.

11. The more obliquely a flat surface is viewed, the more contracted it appears, as if it has fewer parts. This is because, between the outer rays forming the angle, fewer are intercepted from those rays which, due to the curves of the half-spheres, tend elsewhere rather than into the eye. This is argued again from flat mirrors and the foreshortening of a painting. 454
12. The distance of an object is perceived from the interception of things that lie between it and the eye. Things seen by adjacent rays appear touching each other, even if they are very far apart. Why do dogs bark at the Moon? The correction of such appearances is the work of the mind. Why is an image seen beyond a mirror? 455
13. An object is seen larger and more distinct through a telescope or a convex lens because the glass is larger than the pupil. Thus, more small parts of the same sections send rays into the glass. These rays are refracted and consequently more of them reach the pupil than would reach it with the naked eye. The same happens when the pupil is dilated. 456
14. Using the example of a mite a microscopic animal (whose rays are poured into the whole pupil and the convex glass of a microscope, only to meet by refraction inside the eye), it is taught that visible rays are spread not only from a circumference to a center, but also from a center to a circumference. same page.
15. The latter point concerns the paradox in article 17 about distinct vision and reading with only one eye, and about the denial of the convergence of visual axes. It is said that this contradicts not the demonstration of optical scientists, but their supposition. What was said about the parallax of the eyes is repeated. 457.
16. The parallax which comes from both eyes,