rature. 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. They (Sirius, Vega, etc.) are, in fact, known as
"hydrogen stars," and their temperature is generally computed at between
20,000 and 30,000 degrees C. A few stars, such as Procyon and Canopus,
seem to indicate a stage between them and the yellow or solar type.
But we may avoid finer shades of opinion and disputed classes, and
be content with these clear stages. We begin with stars in which only
hydrogen and helium, the lightest Of elements, can be traced; and the
hydrogen is in an unfamiliar form, implying terrific temperature. In
the next stage we find the lines of oxygen, nitrogen, magnesium, and
silicon. Metals such as iron and copper come later, at first in a
primitive and unusual form. Lastly we get the compounds of titanium
and carbon, and the densely shaded spectra which tell of the thickly
gathering vapours. The intense cold of space is slowly prevailing in the
great struggle.

What came before the star? It is now beyond reasonable doubt that the
nebula--taking the word, for the moment, in the general sense of a
loose, chaotic mass of material--was the first stage. Professor Keeler
calculated that there are at least 120,000 nebulae within range of
our telesco