490 



Prof. A. Smithells on the 



T). 



77, 1858, and vol. cvii. 



Wiillner (Togg. Ann. vol. cv 

 p. 533, 1859). 



Wiillner gave no maps, and his readings are merely those 

 of the scale of his instrument ; it is therefore a considerable 

 labour to follow and test his detailed verbal descriptions. 

 The descriptions are complicated chiefly by the fact that one 

 of the spectra involved is developed in various degrees of 

 detail according to the pressure of the gas. This is the oxy- 

 carbon spectrum, mapped in its fullest development by 

 Angstrom & Thalen. Besides this spectrum there are also 

 involved the Swan spectrum, the carbon line spectrum, and 

 the oxygen spectrum. The oxycarbon spectrum can always 

 be recognized at once by the edges of its principal bands, and 

 in the following description I do not distinguish between the 

 different degrees of its development. 



An ordinary Pliicker tube, sealed to the pump, was filled 

 with carbon dioxide prepared from the liquefied gas and dried 

 over phosphoric oxide. The pressure was reduced, and the 

 following table marks the chief consecutive changes : — 



Stages of 

 Edit mixtion. 



4. 



5. 



Ordinary discharge. 



Faint oxycarbon (linear 

 discbarge). 



Bright oxycarbon (glow). 



Brighter oxycarbon. 



Very bright oxycarbon. 



Fading oxycarbon. 



Later stages. The oxycarbon fades slowly. 



Condensed discharge. 

 (Jar and air-gap.) 



Carbon line and oxygen 

 line. 



As in previous stage. 



With medium gap 

 bright Swan; with 

 wide gap as in pre- 

 vious stage. 



The spectrum changes 

 from oxycarbon to 

 Swan to carbon and 

 oxygen line as the 

 gap is widened. 



The spectrum changes 

 from oxycarbon di- 

 rect to carbon and 

 oxygen line as the 

 gap is widened. 



As before, fading 

 slowly. 



Explanation of the Remits obtained with the Oxides of Carbon. 



The usual explanation of the results just described is as 

 follows: — The two oxides of carbon yield under different 

 conditions three spectra in which carbon is involved. Two of 



