The veil is growing thicker; the
life is ebbing from the great frame. Then the star sinks below
the range of visibility, and one would think that we can follow
the dying world no farther. Fortunately, in the case of Algol and
some thirty or forty other stars, an extinct sun betrays its
existence by flitting across the light of a luminous sun, and
recent research has made it probable that the universe is strewn
with dead worlds. Some of them may be still in the condition
which we seem to find in Jupiter, hiding sullen fires under a
dense shell of cloud; some may already be covered with a crust,
like the earth. There are even stars in which one is tempted to
see an intermediate stage: stars which blaze out periodically
from dimness, as if the Cyclops were spending his last energy in
spasms that burst the forming roof of his prison. But these
variable stars are still obscure, and we do not need their aid.
The downward course of a star is fairly plain.
When we turn to the earlier chapters in the life of a star, the
story is less clear. It is at least generally agreed that the
blue-white stars exhibit an earlier and hotter stage. They show
comparatively little absorption, and there is an immense
preponderance of the lighter gases, hydrogen and helium.
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