the parts
into which they may be divided are conceived as fragments of the
things, and as of the same general nature as the wholes of which they
are parts. Yet the chemist and the physicist tell us that these same
extended things are not really continuous, as they seem to us to be,
but consist of swarms of imperceptible atoms, in rapid motion, at
considerable distances from one another in space, and grouped in
various ways.

What has now become of the world of realities to which the plain man
pinned his faith? It has come to be looked upon as a world of
appearances, of phenomena, of manifestations, under which the real
things, themselves imperceptible, make their presence evident to our
senses. Is this new, real world the world of things in which the plain
man finds himself, and in which he has felt so much at home?

A closer scrutiny reveals that the world of atoms and molecules into
which the man of science resolves the system of material things is not,
after all, so very different in kind from the world to which the plain
man is accustomed. He can understand without difficulty the language
in which it is described to him, and he can readily see how a man may
be led to assume its existence.

The atom is not, it is true, directly perceivable by sense, but it is
conceived as though it and its motions were thus perceivable. The
plain man has long known that things consist of parts which remain,
under some circumstances, invisible. When he approaches an object from
a distance, he sees parts which he could not see before; and what
appears to the naked eye a mere speck without perceptible parts is
found under the microscope to be an insect with its full complement of
members. Moreover, he has often observed that objects which appear
continuous when seen from a distance are evidently far from continuous
when seen close at hand. As we walk toward a tree we can see the
indefinite mass of color break up into discontinuous patches; a fabric,
which presents the appearance of an unbroken surface when viewed in
certain ways may be seen to be riddled with holes when held between the
eye and the light. There is no man who has not some acquaintance with
the distinction between appearance and reality, and who does not make
use of the distinction in common life.

Nor can it seem a surprising fact that different combinations of atoms
should exhibit different properties. Have we not always known that
things in combination