inert
stones, and, guided by the volition, the skill, and possibly at times
by the whip of the architect, placing them in their proper positions.
The blocks, in this case, were moved and posited by a power external
to themselves, and the final form of the pyramid expressed the thought
of its human builder.

Let us pass from this illustration of constructive power to another of
a different kind. When a solution of common salt is slowly
evaporated, the water which holds the salt in solution disappears, but
the salt itself remains behind. At a certain stage of concentration
the salt can no longer retain the liquid form; its particles, or
molecules, as they are called, begin to deposit themselves as minute
solids--so minute, indeed, as to defy all microscopic power. As
evaporation continues, solidification goes on, and we finally obtain,
through the clustering together of innumerable molecules, a finite
crystalline mass of a definite form. What is this form? It sometimes
seems a mimicry of the architecture of Egypt. We have little pyramids
built by the salt, terrace above terrace from base to apex, forming a
series of steps resembling those up which the traveller in Egypt is
dragged by his guides. The human mind is as little disposed to look
without questioning at these pyramidal salt-crystals, as to look at
the pyramids of Egypt, without enquiring whence they came. How, then,
are those salt-pyramids built up?

Guided by analogy, you may, if you like, suppose that, swarming among
the constituent molecules of the salt, there is an invisible
population, controlled and coerced by some invisible master, placing
the atomic blocks in their positions. This, however, is not the
scientific idea, nor do I think your good sense will accept it as a
likely one. The scientific idea is, that the molecules act upon each
other without the intervention of slave labour; that they attract each
other, and repel each other, at certain definite points, or poles, and
in certain definite directions; and that the pyramidal form is the
result of this play of attraction and repulsion. While, then, the
blocks of Egypt were laid down by a power external to themselves,
these molecular blocks of salt are self-posited, being fixed in their
places by the inherent forces with which they act upon each other.

I take common salt as an illustration, because it is so familiar to us
all; but any other crystalline substance would answer my purpose
e