area in it; the ring would become a sphere; we should have the
first, and outermost, planet circling round the sun. Other rings
would successively be detached, and form the rest of the planets;
and the sun is the shrunken and condensed body of the nebula.

So simple and beautiful a theory of the solar system could not
fail to captivate astronomers, but it is generally rejected
to-day, in the precise form which Laplace gave it. What the
difficulties are which it has encountered, and the modifications
it must suffer, we shall see later; as well as the new theories
which have largely displaced it. It will be better first to
survey the universe from the evolutionary point of view. But I
may observe, in passing, that the sceptical remarks one hears at
times about scientific theories contradicting and superseding
each other are frivolous. One great idea pervades all the
theories of the evolution of worlds, and that idea is firmly
established. The stars and their planets are enormous
aggregations of cosmic dust, swept together and compressed by the
action of gravitation. The precise nature of this cosmic dust--
whether it was gas, meteorites and gas, or other particles-- is
open to question.

As we saw in the first chapter, the universe has the word
evolution written, literally, in letters of fire across it. The
stars are of all ages, from sturdy youth to decrepit age, and
even to the darkness of death. We saw that this can be detected
on the superficial test of colour. The colours of the stars are,
it is true, an unsafe ground to build upon. The astronomer still
puzzles over the gorgeous colours he finds at times, especially
in double stars: the topaz and azure companions in beta Cygni,