Dissertation on a Solid Body Naturally Contained Within a Solid

DE SOLIDO INTRA SOLIDVM &c.

They are public; they are those which all, from every household, proclaim: Peripatetics, Academics, Stoics, Cynics. And truly, those principles of Natura Nature cannot fail to be best which are common, which are public, and which all, from every school—both those eager for novelty in everything and those studious of ancient dogmas—are bound to admit.

Therefore, I do not determine whether the particles of a natural body can be changed in regard to their figure or cannot be changed; whether there are or are not small empty spaces; whether there is, in those particles, besides extension and hardness, some other thing unknown to us. For these are not public voices, and it is a weak argument to deny that there is something else in a certain thing simply because I do not observe something else there.

But, without hesitation, I assert:

1. That a natural body is a collection of insensible particles accessible to the operations emanating from a magnet, fire, and sometimes even light, in whatever way—whether between the particles, within the particles themselves, or both—open passages may be found.

2. That the solid differs from the fluid in this: that in a fluid the insensible particles are in perpetual motion and move away from one another, whereas in a solid, although the insensible particles may move, they almost never move away from one another as long as that solid remains solid and intact.