the hand has not energies sufficient, within itself, to resist
effectually both the stone and earth.--Action cannot exist in bodies
without re-action. A body that experiences an impulse, an attraction, or
a pressure of any kind, if it resists, clearly demonstrates by such
resistance that it re-acts; from whence it follows, there is a concealed
force, called by these philosophers _vis inertia_, that displays itself
against another force; and this clearly demonstrates, that this inert
force is capable of both acting and re-acting. In short, it will be
found, on close investigation, that those powers which are called
_dead_, and those which are termed _live_ or _moving_, are powers of the
same kind; which only display themselves after a different manner.
Permit us to go a greater distance yet. May we not say, that in those
bodies, or masses, of which their whole become evident from appearances
to us to be at rest, there is notwithstanding, a continual action, and
counter-action, constant efforts, uninterrupted or communicated force,
and continued opposition? In short, a _nisus_, by which the constituting
portions of these bodies press one upon another, mutually resisting each
other, acting and re-acting incessantly? that this reciprocity of
action, this simultaneous re-action, keeps them united, causes their
particles to form a mass, a body, and a combination, which, viewed in
its whole, has the appearance of complete rest, notwithstanding no one
of its particles really ceases to be in motion for a single instant?
These collective masses appear to be at rest, simply by the equality of
the motion--by the responsory impulse of the powers acting in them.

Thus it appears that bodies enjoying perfect repose, really receive,
whether upon their surface, or in their interior, a continual
communicated force, from those bodies by which they are either
surrounded or penetrated, dilated or contracted, rarified or condensed:
in fact, from those which compose them; whereby their particles are