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212 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, 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, as well as the purposes which it has to fulfil in the animal economy—"the contraction of the chest (expiration)