156 On the Spectra of Ignited Gases and Vapours, [Mar. 3, 



which at the highest attainable temperature begin to expand, so that the 

 spectrum tends to become continuous. 



The authors think it probable that the three different spectra of the 

 emitted light depend upon three allotropic states which nitrogen assumes 

 at different temperatures. 



By similar methods the authors obtained two different spectra of sul- 

 phur, one of the first and one of the second order. The spectrum of the 

 first order exhibited channeled spaces, like one of the two spectra of that 

 order of nitrogen ; but the direction in which the depth of shading in- 

 creased was the reverse of what was obsei'ved with nitrogen, the darker 

 side of each channeled space being in the case of sulphur directed towards 

 the red end of the spectrum. 



Selenium, like sulphur, shows two spectra, one of the first and one of the 

 second order. 



Incandescent carbon, even in a state of the finest division, gives a 

 continuous spectrum. Among the gases which by their decomposition, 

 whether in flame or in the electric current, give the spectrum of carbon, 

 the authors describe particularly the spectra of cyanogen and defiant gas 

 when burnt with oxygen or with air, and of carbonic oxide, carbonic acid, 

 marsh-gas, defiant gas, and methyl rendered incandescent by the electric 

 discharge ; they likewise describe the spectrum of the electric discharge 

 between electrodes of carbon in an atmosphere of hydrogen. The spectrum 

 of carbon examined under these various conditions showed great varieties, 

 but all the different types observed were represented, more or less com- 

 pletely, in the spectrum of cyanogen fed with oxygen. The authors think 

 it possible that certain bands, not due to nitrogen, seen in the flame of 

 cyanogen, and not in any other compound of carbon, may have been due 

 to the undecomposed gas. 



The spectrum of hydrogen, as obtained by a small Ruhmkorff^s coil, 

 exhibited chiefly three bright lines. With the large coil employed by the 

 authors, the lines slightly and unequally expanded. On interposing the 

 Ley den jar, and using gas of a somewhat higher pressure, the spectrum 

 was transformed into a continuous one, with a red line at one extremity, 

 while at a still higher pressure this red line expanded into a band. 



The authors also observed a new hydrogen spectrum, corresponding to 

 a lower temperature, but having no resemblance at all to the spectra of the 

 first order of nitrogen, sulphur, &c. 



Oxygen gave only a spectrum of the second order, the different lines of 

 which, however, expanded under certain circumstances into narrow bands, 

 but very differently in different parts of the spectrum. 



Phosphorus, when treated like sulphur, gave only a spectrum of the 

 second order. 



Chlorine, bromine, and iodine, when examined by the electric discharge, 

 gave only spectra of the second order, in which no two of the numerous 

 spectral lines belonging to the three substances were coincident. The 



