1880.] Note on the History of the Carbon Spectrum. 493 



On the ground of observing these two characteristic groups of lines 

 ,f and 6 (our seven blue and six violet nitrocarbon bands) in the spark 

 spectra of carbonic oxide, cyanogen, and naphthaline, Dr. Watts was 

 entitled at the time to infer that they must be due to the common 

 element carbon. Dr. Watts has, however, made many experiments on 

 the carbon spectrum since the date of that paper, and to neglect to 

 take into consideration papers published by him since 1869 is to mis- 

 represent his position. In the "Phil. Mag." for 1874, he wrote in a 

 "Note on the Carbon Spectrum" as follows : — " In the ' Phil. Mag.' 

 for October, 1869, I described four different spectra as spectra of 

 carbon. One of them was the ordinary spectrum from hydrocarbon 

 flames, first described by Swann ; the second was the spectrum ob- 

 tained from vacuum tubes inclosing carbonic oxide, carbonic anhy- 

 dride, or defiant gas ; the third was the spectrum of the Bessemer 

 flame ; and the fourth, the high tension spark in carbonic anhydride 

 or carbonic oxide. 



" I have since shown (' Phil. Mag.,' 1873) that the Bessemer flame 

 spectrum, instead of being a spectrum of carbon, is the spectrum of 

 manganese oxide ; and I have had now to add the result of recent 

 observations, which show that the second spectrum also is due, not 

 to carbon itself, but to some oxide of carbon. This spectrum was held 

 to be a spectrum of carbon because it was common to compounds of 

 carbon, with hydrogen and with oxygen. 



" I have now found that it is not given by spectral tubes inclosing 

 olefiant gas if special care be taken to exclude all traces of oxygen. 



. We have therefore only one spectrum which can be proved 

 to be due to carbon — that, namely, which is common to the flame of 

 olefiant gas or cyanogen, the electric discharge in cyanogen or carbonic 

 oxide at the ordinary pressure, and to the electric discharge in vacuum 

 tubes inclosing cyanogen, olefiant gas, or hydrocarbons, such as benzol." 



We infer from this, that the groups £ and 6 (our seven blue and six 

 violet nitrocarbon bands), which are certainly not common to all the 

 spectra here enumerated, are not included in the one spectrum which 

 Dr. Watts at that time assigned to carbon. However that may be, it 

 is unnecessary to say more about it here, for we have quoted enough 

 to show that Dr. Watts' conclusions, in 1869, were not so certain that 

 they could now be quoted as authoritative against the inferences drawn 

 from later observations, and that we did our subject no injustice in 

 making no more particular allusions to them than we did. 



But, further, after describing an experiment with carbon tetra- 

 chloride, Mr. Lockyer says: — "This result, which entirely endorses 

 the work of Attfield and Watts, has been controlled by many other 

 experiments." If we may assume that the work of Attfield and Watts 



cyanogene, qui est remarquable par l'eclat vif des raies, n'est pas pur, mais mel6 

 des raies des carbures d'bydrogene, dont le splendeur est encore plus raagnifique." 



