of many others of which we know nothing, because they have not yet
become accessible to our senses. From the continual action and re-action
of these beings, result a series of causes and effects; or a chain of
motion guided by the constant and invariable laws peculiar to each
being; which are necessary or inherent to its particular nature--which
make it always act or move after a determinate manner. The different
principles of this motion are unknown to us, because we are in many
instances, if not in all, ignorant of what constitutes the essence of
beings. The elements of bodies escape our senses; we know them only in
the mass: we are neither acquainted with their intimate combination, nor
the proportion of these combinations; from whence must necessarily
result their mode of action, their impulse, or their different effects.

Our senses bring us generally acquainted with two sorts of motion in the
beings that surround us: the one is the motion of the mass, by which an
entire body is transferred from one place to another. Of the motion of
this genus we are perfectly sensible.--Thus, we see a stone fall, a ball
roll, an arm move, or change its position. The other is an internal or
concealed motion, which always depends on the peculiar energies of a
body: that is to say, on its _essence_, or the combination, the action,
and re-action of the minute--of the insensible particles of matter, of
which that body is composed. This motion we do not see; we know it only
by the alteration or change, which after some time we discover in these
bodies or mixtures. Of this genus is that concealed motion which
fermentation produces in the particles that compose flour, which,
however scattered, however separated, unite, and form that mass which we
call BREAD. Such also is the imperceptible motion by which we see a
plant or animal enlarge, strengthen, undergo changes, and acquire new
qualities, without our eyes being competent to follow its progression,
or to perceive the causes which have produced these effects. Such also