Complete Works, Volume Three

of Sections, Parts, and Books

...must be considered natural because of the aforementioned uniformity. All horizontal motion seems by its nature uniform and perpetual. This is understood by the example of a globe of uniform material. If it were moved across a perfectly round and polished surface of the earth, it would seem to revolve both uniformly and perpetually. 488

11. If the downward motion of a stone is violent and comes from an external principle, it must therefore be caused by pushing, pulling, or both. The pushing force can be nothing other than the air pressing down from above. Just as the air resists a stone striving upward, it pursues one tending downward. The force of air in pushing, though it is a fluid, is proved by various effects. It is seen especially in fire-based original: "pyriis," referring to gunpowder-based artillery and air-powered catapults. However, the force of air alone is not sufficient to produce that downward motion. 489

12. The attracting cause can be none other than the Earth itself. The Earth possesses an infinite power to hold and pull back all its parts, as listed here. The analogy, or rather the identical nature, of the Magnet and the Earth is explained briefly. It does not seem that the action of either upon attracted things occurs except by the emission of very subtle corpuscles term: corpuscles (minute physical particles that Gassendi believed mediated all physical forces) that entice them. No physical action occurs without contact or at least the intervention of some physical organ. This is illustrated by the example of a scent original: "halitus," a breath or vapor transmitted from a fragrant object into the nostrils. 491

13. The same occurs regarding the other senses. The corpuscles that soothe the senses are shaped differently than those that irritate them. This is again argued from the sense of smell. The inexpressible subtlety of these corpuscles is shown to be probable. Sympathy and antipathy do not exist except through these particles acting as little organs. Analogous particles must correspond in the receiving organ. For example, there are specific particles in the nostrils, and not in other parts, that respond to the corpuscles of scent. There must also be analogous little pores in the objects that are moved by them. 492

14. The chief difficulty is how the attraction of iron by a magnet occurs through emitted corpuscles. It happens perhaps by rays created by the constant emission of those corpuscles. These are refracted original: "refractisque," meaning turned or bent back in the attracted object toward the perpendicular line. One should also consider how compression and attraction in the magnet follow from angles made like elbows in the iron. The reason for certain effects is given here. The action of electrical things term: electricorum (referring to the attractive properties of amber and similar materials, then called "electrics") can be understood from this. 493

15. The attractive force of the Earth is exerted just like the force of a magnet. It is greater nearby than far away. A stone placed in "imaginary spaces" This refers to the infinite void outside the created universe, a common concept in seventeenth-century physics. would remain at rest there, whether the World existed or not. It would even rest in the middle of the air if that space were made entirely empty. It moves now only because it is pulled. Even a huge rock would be very easily moved if this attraction were restrained. Downward motion is slowest at the very beginning. The force impressed on a projectile is weakened because the attraction of the Earth continually counteracts original: "refringat," literally breaks or refracts the motion it. Therefore, weights, whether large or small and especially if they are of the same material, fall with equal velocity. 494

16. If motion were once impressed on a stone placed in imaginary spaces, it would be uniform and perpetual because of the lack of counteracting attraction. This is confirmed by the earlier points about the uniformity of horizontal motion. It is also seen in the constancy of motion in a hanging object a pendulum. Its swinging out and back are gradually slowed and finally cease primarily because of the resistance of the cord itself and its parts. 495

17. The simple attraction of the Earth can move a stone from rest in the air and overcome the resistance of the air beneath it. If a moving object is struck by one blow and then struck continually by several similar blows, its velocity will continually increase. A stone in the air receives continual "blows" from the Earth, the air, or both. It cannot help but be continually accelerated. If it were moved by only one simple cause, its velocity would increase in a simple sequence (1, 2, 3). However, it actually increases according to the series of odd numbers starting from one (1, 3, 5, 7). 496

18. Both causes are to be joined. In the first moment, there is one blow from the attracting Earth. In the second moment, there are two: one from the attracting Earth and another from the pushing air. Consequently, there are two in each moment. Thus, since all the impulses remain, there is 1 in the first moment and 3 in the second.