VII. Further observations on the spectra of the sun, and of some of the stars and nebulæ, with an attempt to determine therefrom whether these bodies are moving towards or from the earth

Abstract

The author states that at the time of the publication of the “Observations on the Spectra of the Fixed Stars,” made jointly by himself and Dr. W. A. Miller, Treas. R. S., they were fully aware that the direct comparisons of the bright lines of terrestrial substances with the dark lines in the spectra of the stars, which they had accomplished, were not only of value for the more immediate purpose for which they had been undertaken, namely, to obtain information of the chemical constitution of the investing atmospheres of the stars, but that they might possibly serve to reveal something of the motions of the stars relatively to our system. If the stars were moving towards or from the earth, their motion, compounded with the earth’s motion, would alter to an observer on the earth the refrangibility of the light emitted by them, and consequently the lines of terrestrial substances would no longer coincide in position in the spectrum with the dark lines produced by the absorption of the vapours of the same substances existing in the stars. The method employed by them would certainly have revealed an alteration of refrangibility as great as that which separates the lines D. They had, therefore, proof that the stars which they had examined, among others Aldeharan, α Orionis, β Pegasi, Sirius, α Lyræ, Capella, Arcturus, Castor, Pollux, were not moving with a velocity which would be indicated by such an amount of alteration of position in a line.