Atigust 5, 1880] 



NATURE 



311 



In a photograph of the spectrum of the electric arc (with 

 a weak battery) between carbon poles in an atmosphere 

 of chlorine, the blue flutings alone are visible, whilst, when 

 the spark is similarly photographed, the ultra-violet 



flutings and the blue line (4266) are also visible, whilst 

 the blue flutings become fainter. 



From this we may assume, in accordance with the 

 working hypothesis of a series of dift'erent temperature 



Highest temperature. 

 Intermediate. 

 Lowest temperature. 



Fig. 3. — Action of three different temperatures on a hypothetical substance, assuming three stages of complete dissociation. 



furnaces, as set forth in the paper of December, 1878 (see 

 Fig. 3), that the different flutings and the line correspond 

 to different temperature spectra, the blue flutings to the 

 lowest and the blue line to the highest temperature, whilst 

 the ultra-violet flutings occupy an intermediate position. 

 According to this working hypothesis there should be a 



Inter- /' 

 mediate) 2 



series of horizons forming a perfect gradation between the 

 spectrum which contains the blue line alone and that which 

 contains the blue fluting alone (Fig. 4). In comparing the 

 spectra of carbon under different conditions, I find this to 

 be true. The bliti line tiever appears in conjunction -with 

 /he blue flutings, unless the ultra--riokt flutings are also 



lighcjl Tempeiature.p 



Inter- /' 

 mediate I 2 



FlG.'4.— Spectra of the byj-cl 



present. In other words, the highest and the lov^est 

 h\pothetical temperature spectra are never visible to- 

 gether without the spectrum of the intermediate hypo- 

 thetical temperature. 



But this is not all. By placing the spectra of the sub- 

 stances at different heat-levels, so to speak, I was enabled 



Highest temperature. 



Lowest lemperatiu-e 



Lowe't Temperature. 



net ccnpletely disrcciyte 



to construct a map, which not only indicates the^mere 

 presence or absence of the lines and their relative 

 intensities, but shows a perfect gradation between the 

 spectrum which contains the line alone [and that which 

 contains the blue flutings alone (Fig. 5). I woifld point 

 out that there is nothing theoretical in this map. All the 



Spark in CuHg 

 and CHIg. \ 



Spark CO. 



„ CO.. 



„ CN. 



„ CS. 



Arc in CI ( b). 

 „ CI (C). 



Fig. <;.— The photographed spectra of some carbon compounds, 



horizons depicted are copied from photographs of carbon 

 under the conditions indicated, and theory has merely 

 enabled me to arrange them in order. 



seen that, while the blue line gradually thins out, the ultra- 

 violet flutings appear first and grow in intensity. As 

 these increase the blue ^flutings become visible, and 



This map I submit, therefore, bears out the hypothesis ' further, as the latter augments and the line disappears, 

 of differences of temperature indicated above, for it is ■ the ultra-violet flutings gradually die out altogether. 



