Abstract
VI.
IN the first place, then, what does the spectroscope tell us with regard to the radiation from the sun and the stars? And here I ask you to neglect and banish from your minds for a time any idea of those dark lines in the solar spectrum that I drew your attention to on a former occasion. I hope I shall be able to explain them satisfactorily to you afterwards, but for the present I wish you merely to take the fact that our sun, but for the dark lines, would give us a continuous spectrum. The spectrum of the stars is very much like the spectrum of the sun. In Fig. 34 is seen a representation of the spectra of two stars, a Orionis and Aldebaran, mapped with the minutest care by Dr. Miller and Mr. Huggins. In both cases we should have a continuous spectrum but for the presence of the dark lines. I think you will see in a moment what I am driving at. Suppose the sun or stars composed of only sodium vapour, for instance, it is clear that their light analysed by the prism would give us no great indication of a continuous spectrum, we should merely get one bright line in the orange. But neglect the dark lines for a moment: dealing merely with the continuous spectrum of the sun and star, it shows that we have a something, whether it be solid or liquid, or whether it be a dense gas or a vapour, competent to give us a continuous spectrum. So we are justified in assuming that sunlight and starlight proceed from thr incandescence of a solid, a liquid or a dense gas or vapour. Again, suppose that instead of looking at the sun or the stars we observe the moon, as Fraunhofer did, as has been (before stated, what will happen? We get a second edition of sunlight, in exactly the same way as we should get a second edition of the sunlight in the case of a reflection of it from a mirror; and therefore, if proof of such a thing were needed, the spectroscope is perfectly competent to show us that the moon gives us sunlight second-hand. The same in the main with Jupiter, Venus, Mars, and the other planets. If we study them and observe the dark lines we find that the lines which we observe are generally the same as those which we find in the spectrum of the sun. There are other points to which I shall have to draw your attention on a future occasion, but on the whole, the teaching of the spectroscope is, that all those planets are lit up by sunlight as we know them to be. FIG. 37.-Spectrum of the Nebulae-i, z, 3, lines observed. Above, the solar speclrum is shown from l· to?; below, the bright lines of magnesium, nitrogen, barium, and hydrogen, in the corresponding part of the spectrum.
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LOCKYER, J. On the Spectroscope and its Applications . Nature 7, 406–408 (1873). https://doi.org/10.1038/007406a0
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DOI: https://doi.org/10.1038/007406a0