the Nature of Spectra. 89 



Displacement of the Spectra in Solutions. — I am inclined to 

 attribute, at least in part, to chemical influences those dis- 

 placements which the absorption-streaks of various materials 

 undergo according to the substance in which they are dis- 

 solved — especially in the case of organic colouring matters, 

 the quickly commencing decomposition of which in solutions 

 indicates the chemical influence of the solvents. The influ- 

 ence of the dispersion of the solvent may be checked, since 

 solutions, for instance, of potassio-chromic oxalate in water 

 and in glycerine show the absorption-streak in exactly the 

 same place in the spectrum, although the dispersions of these 

 two substances are sensibly different. 



The question, finally, which has lately been repeatedly dis- 

 cussed, of the difference of the spectra, both of emission and 

 absorption, of one and the same substance under different 

 conditions (H. W. Vogel and J. Moser), it appears to me may 

 be solved thus (provided the above considerations are true): — ■ 

 Within the molecules of any chemical compound, which are 

 withdrawn from the influence of the molecules in their vici- 

 nity, perfectly definite vibrations take place, conditioning 

 completely determined spectra ; but as soon as these molecules 

 come nearer to one another, or, in liquids or solids, form more 

 complex (multiple) molecules, or, finally, in solutions are in- 

 fluenced also by the action of another substance, the spectra 

 may change their appearance. That two different substances 

 give perfectly identical spectra is thinkable only when the 

 forces acting between the atoms in their molecules are iden- 

 tical. 



It is my intention to test by experiments, and pursue fur- 

 ther, the views which have now been unfolded, and which very 

 well explain a great number of the facts that have hitherto 

 been observed. But for this, it is before all things necessary 

 to examine the spectra under completely determined condi- 

 tions of temperature and pressure. 



The most convenient means for the production of elevated 

 temperatures, such as are necessary to call forth gas-spectra, 

 is, decidedly, the electric spark. Hence the temperatures 

 generated by it must be exactly ascertained ; and, above all, 

 we must accurately settle whether it calls forth the luminous 

 phenomena by elevation of temperature alone. 



In order first to decide the last point, I tried whether, in 

 mixtures of two gases through which a discharge passes, the 

 spectra of both substances constantly make their appearance, 

 or only one of them. 



