Studies in spectrum analysis / by J. Norman Lockyer.

  • Norman Lockyer
Date:
1904
Catalogue details

Licence: In copyright

Credit: Studies in spectrum analysis / by J. Norman Lockyer. Source: Wellcome Collection.

    63/302 (page 45)
    the giving out of light by a body, whether simple or compound, which retains the solid or liquid form while in a state of incandescence. A white-hot poker and glowing fluid iron are familiar instances of such a light source. In 2-8 we have examples of so-called line or band spectra produced by vapours or gases giving out light. These require detailed examination. In 2, 3, we have spectra belonging to two elementary metallic bodies— sodium and magnesium. It will be seen how different they are, and how easy it is to bear in mind or to map such an allocation of lines, so that when produced from an unknown body the existence of either can be detected by such spectral examination. This part of the plate might have contained the spectra of all the metallic bodies in a state of vapour, and it would still have been abundantly apparent that each was so distinct from all the rest, that there would be little difficulty in recog- nizing the dissimilarity. In 4 we have a specimen of the spectrum of a compound body, in this case a salt of strontium—other salts have equally characteristic spectra. Here again is a complete separation from 2 and 3, and an equally complete dissimilarity is observed even in the spectra of compounds which ordinarily occur in the state of gas. In 5 and 6 we have bands of light occupying the same position in the spectrum, but they are wide in one case and narrow in the other. We are dealing with the same substance—hydrogen—at differ- ent pressures. In 7 and 8 we have left the earth and have sought for