SPECTRA OF IGNITED GASES AND VAPOTJRS. 
13 
(N ii 5, N iv 6, N jv 7) were specially observed. When we made use of twelve of Grove’s 
elements ranged into three sets of four combined ones, the current even passed after 
we interposed the Jar, and we got a most dazzling second spectrum of the gas. The 
bright lines of this spectrum, rising from a ground itself brighter than it usually is, 
ceased at an increased brilliancy to be well defined. The two brilliant green lines both 
expanded, and were united into a single broad line ; the double yellow lines, though 
expanded, yet remained double. The spectrum was progressing towards a continuous one . 
33. In recapitulating, we get the following results: — 
Nitrogen in the state of greatest rarefaction, such as may be obtained by Geissler’s 
exhauster, like other gases does not allow the induction current to pass through. But 
when its tension is only a small fraction of a millimetre, the current begins to pass and 
renders the gas luminous. Below a certain limit of temperature ignited nitrogen sends 
out a golden-coloured light, giving the spectrum of bands. Above this limit the colour 
of the light is replaced by a bluish violet, the spectrum of channeled spaces replacing 
simultaneously the spectrum of bands. When, by means of the intercalated jar for 
instance, the temperature rises to a second higher limit, the light of the gas, becoming 
white and most brilliant, gives, if analyzed by the prism, a spectrum of quite a different 
description : bright lines of different intensity, with the colour indicated by the place 
they occupy, rise from a dark ground. By increasing the power of the discharge these 
lines become more brilliant, but the brilliancy does not increase in the same ratio for 
them all. New bright lines appear, which formerly, on account of their extreme faint- 
ness, were not visible ; but the number of such lines is not unlimited. By increasing 
the heat of the ignited nitrogen to the last extremity, the lines, especially the brighter 
ones, gradually expand, approaching thus to a continuous spectrum. 
34. Those spectra which are composed of larger bands showing various appearances 
according to their being differently shaded by subtle dark lines , we generally call spectra 
of the first order. In the same spectrum the character of the bands is to a certain extent 
the same, the breadth of the bands varies in a more or less regular way. On the con- 
trary, those spectra in which brilliant coloured lines rise from a more or less dark ground, 
we call spectra of the second order. 
Ignited nitrogen therefore exhibits, if its temperature increase, successively two 
spectra of the first and one of the second order. 
35. In the case of sulphur, which we may select as another instance, there are two 
different spectra, one of the first and one of the second order. 
In common air the flame of sulphur gives a continuous spectrum ; if fed with oxygen 
we get a spectrum of the first order, but it is faint and its bands are not well defined. 
In order to get the sulphur-spectrum most perfect, we must recur to our spectral tubes. 
A doubly bent short tube (6), into which we introduced a small quantity of sulphur, was 
evacuated by means of Geissler’s exhauster, and while attached to it heated by a lamp, 
in order to expel as much as possible the moisture it contained. Finally, the mano- 
meter showing no more tension of the remaining gas, the tube was hermetically sealed 
