Drs. Plucker and Hittorf on the Spectra of Ignited Gases. 67 



of sulphur, one of the first and one of the second order. The spec- 

 trum 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 increased was the reverse of what was observed 

 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 decomposi- 

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

 carbon, the authors describe particularly the spectra of cyanogen and 

 olefiant gas when burnt with oxygen or with air, and of carbonic oxide, 

 carbonic acid, marsh-gas, olefiant gas, and methyle rendered incan- 

 descent by the electric discharge ; they likewise describe the spec- 

 trum 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 completely, in the 

 spectrum of cyanogen fed with oxygen. The authors think it pos- 

 sible 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 em- 

 ployed 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, correspond- 

 ing 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 dis- 

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

 numerous spectral lines belonging to the three substances were coin- 

 cident. The authors were desirous of examining whether iodine 

 would give a spectrum of the first order the reverse of the absorption- 

 spectrum at ordinary temperatures. The vapour of iodine in an 

 oxyhydrogen jet gave, indeed, a spectrum of the first order, but it 

 did not agree with what theory might have led us to expect. 



In the electric discharge, arsenic and mercury gave only spectra 

 of the second order. The metals of the alkalies sodium, potassium, 

 lithium, thallium show, even at the lower temperature of Bunsen's 

 lamp, spectra of the second order. 



F2 



