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,
the emerald and red of alpha Herculis, the yellow and rose of eta
Cassiopeiae, and so on. It is at the present time under
discussion in astronomy how far these colours are objective at
all, or whether, if they are real, they may not be due to causes
other than temperature.
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