h color. It had then three bright
hydrogen lines, the strong double sodium line, and others, which
made, it strongly resemble the spectrum of the chromosphere of our
sun. An entirely different result appeared in the fading of these
two stars. In the case of the star in the Crown, the extraordinary
light was the first to fade, leaving the usual stellar spectrum. In
the case of the star in Cygnus, the part of the spectrum belonging
to stellar light was the first to fade, leaving the bright lines;
that is, the gas of one gave way to regular starlight, and the
starlight [Page 226] of the other having faded, the regular light of
the glowing gas continued. By some strange oversight, no one studied
the star again for six months. In September and November, 1877, the
light of this star was found to be blue, and not to be starlight at
all. It had no rainbow spectrum, only one kind of rays, and hence
only one color. Its sole spectroscopic line is believed to be that
of glowing nitrogen gas. We have then, probably, in the star of
1876, a body shining by a feeble and undiscernible light, surrounded
by a discernible immensity of light of nitrogen gas. This is its
usual condition; but if a flight of meteors should raise the heat of
the central body so as to outshine the nebulous envelope, we should
have the conditions we discovered in November, 1876. But a rapid
cooling dissipates the observable light of all colors, and leaves
only the glowing gas of one color.

_Movements of Stars._

We call the stars _fixed_, but motion and life are necessary to all
things. Besides the motion in the line of sight described already,
there is motion in every other conceivable direction. We knew Sirius
moved before we had found the cause. We know that our sun moves
back and forth in his easy bed one-half his vast diameter, as the
larger planets combine their influence on one side or the other.

The sun has another movement. We find the stars in Hercules gradually
spreading from each other. Hercules's brawny limbs grow brawnier
every century. There can be but one cause: we are approaching that
quarter of the heavens. (See [Symbol], Fig. 72.) We are even [Page
227] able to compute the velocity of our approach; it is four miles
a second. The stars in the opposite quarter of the heavens in Argo
are drawing nearer together.

This movement would have no effect on the apparent place of the
stars at either pole, if they were all equally distant; but it
m