So we get the descending scale
of spectra. The dark lines are thinnest and least numerous in the
blue stars, more numerous in the yellow, heavy and thick in the
red. As the body of the star sinks in temperature dense masses of
cool vapour gather about it. Its light, as we perceive it, turns
yellow, then red. The next step, which the spectroscope cannot
follow, will be the formation of a scum on the cooling surface,
ending, after ages of struggle, in the imprisonment of the molten
interior under a solid, dark crust. Let us see how our sun
illustrates this theory.
It is in the yellow, or what we may call the autumnal, stage.
Miss Clerke and a few others have questioned this, but the
evidence is too strong to-day. The vast globe, 867,000 miles in
diameter, seems to be a mass of much the same material as the
earth--about forty elements have been identified in it--but at a
terrific temperature. The light-giving surface is found, on the
most recent calculations, to have a temperature of about 6700
degrees C. This surface is an ocean of liquid or vaporised
metals, several thousand miles in depth; some think that the
brilliant light comes chiefly from clouds of incandescent carbon.
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