10 
DBS. J. PLUCKER AND J. W. HITTORP ON THE 
according to which N n 5, N iv 6, N iv 7, and N v 2, for instance, indicate the brightest 
lines of the groups of the nitrogen-spectrum. 
23. Not only is the general character of the two kinds of spectra we obtained when 
nitrogen was heated in our tubes, either by the direct discharge or by the discharge of 
the interposed Leyden jar, quite different, but the difference is even so great that the 
bright lines of one of the spectra do not in the least fall within the brighter part of the 
bands constituting the other. Thus, for instance, the bright yellow line (N ii 5) falls 
within the nineteenth band, the darkest of all the bands constituting the less refracted 
part of the spectrum ; the bright blue line (N v 2) falls into the darker part of one of 
the channeled spaces. Accordingly it appears by no means probable that by increasing 
the temperature the shaded bands of one spectrum may be transformed gradually into 
the bright lines of the other ; nevertheless it would be desirable to prove by experiment 
that the passage from one spectrum to another is a discontinuous and abrupt one. 
24. For a given nitrogen-tube which without the Leyden jar gives the spectrum of 
bands, and by means of the commonly used jar the spectrum of bright lines, you may 
easily select a jar of smaller covering, which, if intercalated, exhibits the curious phe- 
nomenon of two rival spectra disputing existence with each other. Sometimes one of 
the spectra, sometimes the other appears ; and for moments both are seen simultaneously. 
Especially the brighter lines of the second spectrum abruptly appear in the blue and 
violet channeled spaces of the first, and, according to the fluctuation of the induced 
current, either suddenly disappear again or subsist for some time, and constitute with 
the added fainter lines the second spectrum. 
We obtain in an easier and a continuous way both spectra simultaneously by making 
use of a small Leyden jar, and increasing its charge by an intercalated stratum of air 
the thickness of which increases till the bright lines appear within the bands of the 
primitive spectrum. 
25. By these and other experiments it is evidently proved that ignited nitrogen shows 
two quite distinct spectra. Each bright line of one of these spectra, each of the most 
subtle lines into which, by means of the telescope, the bands of the other are resolved, 
finally depends upon the molecular condition of the ignited gas, and the corresponding 
modification of the vibrating ether within it. Certainly, in the present state of science, 
we have not the least indication of the connexion of the molecular constitution of the 
gas with the kind of light emitted by it ; but we may assert with confidence that, if one 
spectrum of a given gas be replaced by quite a different one, there must be an analogous 
change of the constitution of the ether, indicating a new arrangement of the gaseous 
molecules. Consequently we must admit either a chemical decomposition or an allo- 
tropic state of the gas. Conclusions derived from the whole series of our researches 
led us finally to reject the first alternative and to adopt the other. 
26. The same spectral tube exhibits, in any succession whatever, as often as you like, 
each of the two spectra. You may show it in the most striking way by effecting the 
intercalation of the Leyden jar by means of a copper wire immersed in mercury. As 
