Lectures de Potentia Restitutiva, or of Spring

in its natural state and balance in the universe. These particles are all of the same nature—that is, they have equal mass and equal motion. Because of this, they readily coalesce and join together to form one solid body. This body is not perfectly solid in every part, nor does it completely exclude the surrounding ambient fluidThe "ether" or fluid medium thought to fill all space in 17th-century physics. mentioned previously. Instead, the solid allows this fluid to pass through it in a regular order in many places, yet the particles are close enough that they prevent the fluid from passing between every side of the compounding particles.

The parts of all springy original: "springy"; meaning elastic bodies would recede and fly away from each other if they were not kept together by the heterogeneous original: "Heterogeneous"; meaning diverse or originating from outside the body compressing motions of the surrounding medium, whether that medium is fluid or solid.

Having hinted at these principles, I shall next provide a specific explanation of how they serve to clarify the phenomena original: "Phænomena" of elastic bodies, whether they are solid or fluid.

First, consider solid bodies such as steel, glass, wood, and so on. These have a "spring" or elasticity that acts both inwards and outwards, depending on whether they are compressed or stretched beyond their natural state.

Let the line A B represent a section of such a body, composed of eight vibrating particles, labeled 1, 2, 3, 4, 5, 6, 7, 8. Suppose each of those particles performs a million single vibrations—and consequently a million collisions original: "occursions" with one another—within a single second of time.