Lectures de Potentia Restitutiva, or of Spring

By Congruity and Incongruity, then, I understand nothing else but an agreement or disagreement of Bodies as to their Magnitudes size or physical extent and motions.

I suppose those Bodies to be congruous whose particles have the same Magnitude and the same degree of Velocity, or else an harmonical proportion a mathematical relationship often compared to musical intervals of Magnitude and an harmonical degree of Velocity. And I suppose those to be incongruous which have neither the same Magnitude, nor the same degree of Velocity, nor an harmonical proportion of Magnitude or Velocity.

I suppose, then, the sensible Universe to consist of body and motion.

By Body, I mean something receptive and communicative of motion or progression. Nor can I have any other idea of it; for neither Extension the property of taking up space nor Quantity, hardness nor softness, fluidity nor fixedness, Rarefaction becoming less dense nor Density are the properties of Body itself, but rather of Motion or of something being moved.

By Motion, I understand nothing but a power or progressive tendency of Body according to several degrees of Velocity.

These two always counterbalance each other in all the effects, appearances, and operations of Nature. Therefore, it is not impossible that they may be one and the same; for a little body with great motion is equivalent to a great body with little motion regarding all its sensible effects in Nature.

I further suppose, then, that all things in the Universe that become the objects of our senses are compounded of these two—which we will for the present suppose to be distinct essences, though possibly they may be found hereafter to be only differing conceptions of one and the same essence—namely, Body and Motion. And I suppose that there is no one sensible Particle of matter but owes the greatest part of its sensible Extension to Motion, whatever part of it owes to Body according to the common notion of it: which is, that