apparently an endless variety of spectra
When we apply the spectroscope to celestial objects we find
apparently an endless variety of spectra. We shall illustrate
some of the leading characteristics of these spectra as in
Figs. 13 to 18, inclusive, and Figs. 21, 22, 23 and 24. The
spectra of some nebulae consist almost exclusively of isolated
bright lines, indicating that these bodies consist of luminous
gases, as Huggins determined in 1864; but a very faint
continuous band of light frequently forms a background for the
brilliant bright lines. Many of the nebular lines are due to
hydrogen, others are due to helium; but the majority, including
the two on the extreme right in Fig. 13, which we attribute to
the hypothetical element nebulium, and the close pair on the
extreme left, have not been matched in our laboratories and,
therefore, are of unknown origin. Most of the irregular nebulae
whose spectra have been observed, the ring nebulae, the
planetary and stellar nebulae, have very similar spectra,
though with many differences in the details.[1]
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