produced by the same object upon the same individual,
truth either has no existence, or else it can hardly ever be
attained to by mortal beings. To return, however, to the
doctrine of atoms, Leucippus and Democritus maintained
that, as bodies are distinguished by forms, and forms are
infinite, elementary bodies must be infinite also; but then,
with the exception of fire, which was said to be spherical,
they forgot to specify what the forms are; and they denned
elementary bodies by greatness and smallness as well as
form. Thus, form motion and size are, according to
them, the constituents of these formative atoms, and,
accordingly, the larger atoms which are said to go to the
formation of bodies, are distinguished from the smaller
ones or motes (held to be visible only in the sun-beams),
which, as being endowed with vital properties, are alluded
to, in a succeeding passage, as supporting, through respi-
ration, the life of the animal. In fine, this doctrine of
atoms varying in form and size, constantly moving, and,
through attraction and repulsion, combining with and
separating from one another, prevailed in all the schools
of antiquity; and there may perhaps be traced in it a
faint outline of the present matured theory of atomic
proportion.
Note 2, p. 19. Hence, too, they make breathing,
&c.] This description conveys, under a rude exterior, so
to say, a description of the process of breathing or respi-
ration, as well as the purposes which it has to fulfil in the
animal economy—"the contraction of the chest (expiration)
