346 Professor Liveing, On Differences 



still absent. At still higher pressure the blue and violet bands 

 appeared at the anode as well as at the kathode. By this time 

 the whole tube had become very black with the products of 

 decomposition which could not be removed by pumping. The 

 best observations were obviously those made at first, from which 

 I gather that all the bands above mentioned belong to the kathode 

 glow. In no case, when once the carbonic acid had been 

 thoroughly removed, did I see anything of the spectrum either of 

 carbonic oxide, or of the candle-flame, though the latter is always 

 very brilliant in the flame of cyanogen fed with oxygen. 



The series of bands less refrangible than the blue, so bright in 

 the flame of cyanogen, are not connected with the series in the 

 blue and violet. The latter are very bright, in both arc and 

 spark, between carbon electrodes in nitrogen, without a trace of 

 the former. The latter are degraded on the more refrangible side, 

 while the former are degraded on the less refrangible side, which 

 is such an important difference that I feel sure that the vibrating 

 molecules in which they originate are different. This is probable 

 enough because of the rapid decomposition of cyanogen in the 

 discharge, and the ease with which paracyanogen is produced, but 

 at present I have no evidence for attributing the orange bands to 

 any particular product of cyanogen. 



Coming to the theoretical considerations which the facts 

 observed suggest, we have to account for (1) the two perfectly 

 distinct spectra, at the kathode and anode respectively, of hydrogen, 

 nitrogen, and the halogens, (2) the absence of any anode light in 

 oxygen and sulphur, (3) the identity of kathode and anode 

 spectra in the metallic vapours, and in carbonic oxide, (4) the 

 absence of visible spectra which can be ascribed to the compound 

 molecules of hydrochloric acid and water, while the compound 

 molecules of carbonic oxide and cyanogen give very characteristic 

 spectra, (5) the identity of the spectra of the two oxides of 

 carbon. 



The appearances of the positive column in hydrogen and 

 nitrogen agree well with Professor Thomson's theory 1 that the 

 light of the column is excited by association of the ions, and 

 arises in the positive ions. The head of the column nearly coin- 

 cides with a region in which the strength of the electric field is a 

 maximum, and this would occur where the association of ions is a 

 maximum. Moreover, the spectrum of the head of the column, 

 especially the brightest part of the head of each stria when 

 striation occurs, is essentially that of the anode, and the head of 

 the column is driven from the kathode as the exhaustion proceeds 

 and the free path of the negative ions lengthened, until, when 



1 Phil. Mag. [5], L. 278, 1900, and Conduction of Electricity through Gases,- 

 Cambridge University Press, 1903, 



