Spectrum analysis in its application to terrestrial substances, and the physical constitution of the heavenly bodies / Familiarly explained by the late H. Schellen. Trans. from the 3d enl. and revised German edition by Jane and Caroline Lassell.

  • Heinrich Schellen
Date:
1885
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Licence: Public Domain Mark

Credit: Spectrum analysis in its application to terrestrial substances, and the physical constitution of the heavenly bodies / Familiarly explained by the late H. Schellen. Trans. from the 3d enl. and revised German edition by Jane and Caroline Lassell. Source: Wellcome Collection.

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    thallium melting at a low temperature is quickly volatilized, and the presence of the vapour immediately lessens the resistance in the arc, and consequently lowers the tempera- ture to such an extent that the silver is not volatilized. When the thallium is nearly burnt out, the resistance to the current rapidly increases, and the temperature is thereby so considerably raised that the silver becomes volatilized. The characteristic feature of spectra obtained from luminous vapours or gases is the want of continuity in the succession of the colours. Such a spectrum being composed of isolated coloured bands, irregularly arranged, and separated by dark spaces, is therefore called a discontinuoiis spectrum, a brigJit liue Spectrum, or a vapour spectrum. In the coloured plate (Plate XIV.), Nos. 2, 3, 4, and 5 give the spectra of the vapours of sodium, magnesium, Chloride of Strontium, and hydrogen under great pressure. No. 6 gives the spectrum of the vapour of hydrogen under a low pressure. They exhibit at a glance the great difference that exists between the continuous spectrum (No. i) of incandescent solid and liquid bodies and the discontinuoiis spectra of gases. The vapour of sodium (No. 2) under ordinary circumstances, and when not exposed to an ex- tremely high temperature, gives a spectrum consisting only of one bright orange line shown to be double by the use of sufficient dispersive power.* The spectrum of luminous magnesium vapour (No. 3) consists of very brilliant isolated green and blue lines; but the spectrum of chloride of Strontium is much more complete, and it may serve as an example of the spectrum of a compound substance. The fine lines in the blue green belong solely to the metal Strontium, the broad stripes or channelled spaces to the compound substance, chloride of Strontium. We have seen in the case of brass that when two metals * [There are two other lines in the infra red of the spectrum.]
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