THE 

 . LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



FEBRUARY 1879. 



XL Investigations on the Nature of Spectra (1. Theory ; 

 2. Spectra of Mixed Gases). By Eilhard Wiedemann*. 



SINCE the path-opening investigations of Bunsen and 

 Kirchhoff the spectra of incandescent gases have been 

 subjected to a more searching elaboration ; and it has been re- 

 peatedly endeavoured to ascertain theoretically the reasons for 

 the occurrence of line and band spectra, to discover relations 

 between the individual lines which compose them, as well as 

 to explain the variations which they undergo through pressure 

 and change of temperature. 



As, however, the physicists in question mostly enter more 

 closely only into particular points, and but cursorily touch 

 upon the causes for the spectral lines without bringing them 

 into connexion with other data resulting from the mechanical 

 theory of gases, I have tried, partly in continuation of their 

 considerations, to form for myself a theory of spectral pheno- 

 mena, which should be useful in enabling me to get, first of 

 all, fixed points for a series of experimental investigations, the 

 first part of which I take leave to communicate supplementary 

 to the above theory. 



Theory. 



According to the kinetic theory of gases, the individual mo- 

 lecules contained in them move rapidly in all directions. As 

 Stefan and Van der Waals have inferred from the experiments 

 of Joule and Thomson, between these molecules attractive 



* Translated from a separate impression, communicated by the Author, 

 from Wiedemann's Annalen, vol. v. pp. 500-524. 



Phil. Mag. S. 5. Vol. 7. No. 41. Feb. 1879. H 



