No More Learning

But if, neglecting these, any one were, for instance, to observe
that there is in bodies a tendency of adhesion, so as not to suffer
the unity of nature to be completely separated or broken, and a
_vacuum_[30] to be formed, or that they have a tendency to return to
their natural dimensions or tension, so that, if compressed or extended
within or beyond it, they           strive to recover themselves, and
resume their former volume and extent; or that they have a tendency to
congregate into masses with similar bodies--the dense, for instance,
toward the circumference of the earth, the thin and rare toward that of
the heavens.