sun-spot, or the observation
of spots of different sizes, and the long series of successive
steps that mark the rise and decay of stellar life, resemble the
changes that the experimenter brings about as he increases and
diminishes the current in the coils of his magnet or raises and
lowers the temperature of his electric furnace, examining from
time to time the spectrum of the glowing vapors, and noting the
changes shown by the varying appearance of their lines.

[Illustration: Fig. 36. Titanium oxide in red stars.

The upper spectrum is that of titanium in the flame of the electric
arc, where its combination with oxygen gives rise to the bands of
titanium oxide (Fowler). The lower strip shows the spectrum of
the red star Mira (Omicron Ceti), as drawn by Cortie at Stonyhurst.
The bands of titanium oxide are clearly present in the star.]

[Illustration: Fig. 37. Titanium oxide in sun-spots.

The upper strip shows a portion of the spectrum of a sun-spot
(Ellerman); the lower one the corresponding region of the spectrum
of titanium oxide (King). The fluted bands of the oxide spectrum
are easily identified in the spot, where they indicate that titanium
and oxygen, too hot to combine in the solar atmosphere, unite in the
spot because of the cooling produced by expansion in the vortex.]

Astronomical observations of this character, it should be noted, are
most effective when constantly tested and interpreted by laboratory
experiment. Indeed, a modern astrophysical observatory should be
equipped like a great physical laboratory, provided on the one hand
with telescopes and accessory apparatus of the greatest attainable
power, and on the other with every device known to the investigator
of radiation and the related physical and chemical phenomena. Its
telescopes, especially designed with the aims of the physicist and
chemist in view, bring images of sun, stars, nebulae, and other
heavenly bodies within the reach of powerful spectroscopes, sensitive
bolometers and thermopiles, and the long array of other appliances
available for the measurement and analysis of radiation. Its electric
furnaces, arcs, sparks, and vacuum tubes, its apparatus for increasing
and decreasing pressure, varying chemical conditions, and subjecting
luminous gases and vapors to the influence of electric and magnetic
fields, provide the means of imitating celestial phenomena, and of
repeating and interpreting the experiments observed at the telescope.