Perhaps it will be admitted that this is true of such sciences as those
above indicated, but doubted whether it is true of all the sciences,
even of all the sciences which are directly concerned with _things_ of
_some_ sort. For example, to the plain man the world of material
things consists of things that can be seen and touched. Many of these
seem to fill space continuously. They may be divided, but 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