produced that complex combination of tissues and organs constituting the
adult animal or plant. This is the history of all organisms whatever. It
is settled beyond dispute that organic progress consists in a change
from the homogeneous to the heterogeneous.

Now, we propose in the first place to show, that this law of organic
progress is the law of all progress. Whether it be in the development of
the Earth, in the development of Life upon its surface, in the
development of Society, of Government, of Manufactures, of Commerce, of
Language, Literature, Science, Art, this same evolution of the simple
into the complex, through successive differentiations, holds throughout.
From the earliest traceable cosmical changes down to the latest results
of civilisation, we shall find that the transformation of the
homogeneous into the heterogeneous, is that in which Progress
essentially consists.

With the view of showing that _if_ the Nebular Hypothesis be true, the
genesis of the solar system supplies one illustration of this law, let
us assume that the matter of which the sun and planets consist was once
in a diffused form; and that from the gravitation of its atoms there
resulted a gradual concentration. By the hypothesis, the solar system in
its nascent state existed as an indefinitely extended and nearly
homogeneous medium--a medium almost homogeneous in density, in
temperature, and in other physical attributes. The first advance towards
consolidation resulted in a differentiation between the occupied space
which the nebulous mass still filled, and the unoccupied space which it
previously filled. There simultaneously resulted a contrast in density
and a contrast in temperature, between the interior and the exterior of
this mass. And at the same time there arose throughout it rotatory
movements, whose velocities varied according to their distances from its
centre. These differentiations increased in number and degree until
there was the organised group of sun, planets, and satellites, which we
now know--a group which represents numerous contrasts of structure and
action among its members. There are the immense contrasts between the
sun and planets, in bulk and in weight; as well as the subordinate
contrasts between one planet and another, and between the planets and
their satellites. There is the similarly marked contrast between the sun
as almost stationary, and the planets as moving round him with great
velocity; while there