of Sections, Parts, and Books

[...continued] an ant could not be seen in an empty sky for the reason he provides. Why the globe of the Sun could not be seen to move because of the motion he introduced. 468

6. The authors of the atomic theory original: "Atomorum Authores"; Gassendi refers to thinkers like Epicurus and Lucretius who argued that the fundamental building blocks of matter lack secondary qualities do not attribute sensible qualities like color, smell, taste, or heat to atoms. They only grant them size, shape, and weight or motion. They believe qualities arise from the position and order of atoms, and vary through their removal, addition, or rearrangement. 469

7. According to these same authors, bodies are not actually colored in the dark. Instead, light itself provides various colors according to its degrees and the way a body is disposed to refract or reflect light toward the eye. 470

8. Regarding the nature of "true" colors, such as those seen on a pigeon's neck or a peacock's tail. These include the colors in a rainbow or a halo, those cast on a wall by light passing through colored glass, and those painted at the edges of objects by a glass prism original: "trigonum vitreum"; literally a "glass triangle," used here to describe a prism. It lists how many colors appear, their order, and the fourfold amount of refraction involved. ibid.

9. Colors vary as different types of light strike the sense organ. What is the source of white? Is black something different from shadow? The sympathy and antipathy of colors. The necessary mixing of shadows. Regarding colors produced by a prism. The colors of objects are similar to these. Why they are these colors and not others. Concerning the passage of rays near the base or the top of a prism. Regarding these matters, we do nothing but babble original: "balbutimus"; a common expression of scientific humility in early modern texts. 471

10. Sight only perceives colors; it does not judge them. The sense is never deceived because its only role is the perception of appearance. Error belongs only to the mind, which is the source of opinion. 472

11. What kind of impression is made in the brain by an image original: "speciem"; in early optics, this refers to the "species" or formal likeness of an object traveling through the air transmitted into the eye. How this impression allows for thinking, recording, forgetting, remembering, and dreaming. On the nature of these dreams. ibid.

12. The physical cause of why nature allows for an "interspersed" vacuum original: "vacuū interspersum"; Gassendi argued that small voids exist between particles of matter rather than one large, continuous empty space in the air. This vacuum is very small and not separated from the matter. He discusses a heap of grains as a comparison. How is air compressed by force or stretched out with momentum? 473

13. From the events that occur in a free or enclosed heap of grains, it is explained to what extent air admits or avoids a vacuum. By what force a vacuum is prevented in common examples like bellows, a water clock clepsydra: an ancient device that measures time by the flow of water, a vial, or a cup. 474

14. In what sense glass is understood to be penetrated in every direction by a perpendicular ray. The thinness of a light ray and of the tiny bodies and channels within the glass. The surface of glass is partly "full," which causes the reflection of rays, and partly "empty," which allows for their transmission. Reflected rays are missing from transmitted light, and transmitted rays are missing from reflected light. 475

15. A ray is a corpuscle original: "corpusculum"; a tiny physical particle. There is no sensible point in glass that does not contain countless tiny bodies and insensible voids. It is shown that paths for rays to pass through exist from one surface of glass to another in every direction, not only diagonally but also in straight lines. This is explained by a comparison to a mist or cloud, as no glass is more opaque than a mist. The same is shown in water. 476

16. Regarding the response of Liceti Fortunio Liceti was a contemporary scholar who debated Gassendi on the nature of light and the vacuum. The letter is concluded. 477

THREE EPISTLES ON IMPRESSED MOTION

from a moved Mover.

FIRST EPISTLE

Art. 1.

A brief review is given of experiments conducted from a horse, a chariot, and a ship. These prove that if the body we are standing upon is moved, the motion of an object thrown by us happens and appears just as if that body were at rest. page 478

2. Experiments are proposed concerning a ball which, when dropped while one is walking, always runs forward. If thrown backward, it either moves more slowly, falls straight down, or even follows the person by being moved forward. The cause is said to be the motion which the hand (whether it has its own motion or not) receives from the body and impresses upon the ball it touches. ibid.