The most promising method of determining the wave lengths of the stellar spectra is to interpose some absorbent medium.

Theoretical chemistry: an introduction to quantum mechanics, statistical mechanics, and molecular spectra for chemists.

We may thus observe three principal absorption spectra.

This last will include a classification of the spectra, a determination of the wave lengths of the lines, a comparison with terrestrial spectra, and an application of the results to the measurement of the approach and recession of the stars.

To go deeper into this matter, to speculate upon the possible germs, the first vague intimations to the mind of Coleridge of the weird spectra of "The Ancient Mariner," the phantasmagoria of "Kubla Khan," would be, perhaps, over-refining.