SPECTEA OE IGNITED GASES AND YAPOUES. 
9 
entirely stereotype ; all apparent changes result from the different intensity of light. 
The middle part of the spectrum, on the contrary, may much differ from that which we 
have described ; you may even say that this part varies more or less essentially on 
replacing one spectral tube enclosing nitrogen by any other. Sometimes the traces of 
the less refracted bands are seen far beyond H/3, spreading over the channeled part of 
the spectrum ; in other cases the channeled appearance goes in the opposite direction 
as far as the sodium-line, disturbing the character of the bands. 
20. Now, instead of the direct discharge of Ruiimkorff’s large induction coil, let us 
send through the very same spectral tubes the discharge of the interposed Leyden jar. 
The spectrum then obtained (Plate II.) has not the least resemblance to the former one. 
The variously shaded bands which we have hitherto described are replaced by brilliant 
lines on a more or less dark ground. Neither the distribution of these new lines nor 
their relative brightness gives any indication whatever of a law. Nevertheless the place 
occupied by each of them remains under all circumstances invariably the same. If 
exactly determined, not only does each line undoubtedly announce the gas within the 
tube, but the gas may even, without measuring, be recognized at first sight by charac- 
teristic groups into which the lines are collected. 
21. The new spectrum of nitrogen extends towards the red slightly beyond the 
hydrogen-line Ha, which if the gas be not dried with care will be seen simultaneously, 
enclosed by two red nitrogen-lines, the less refracted of which is twice as distant as the 
more refracted. There are in the spectrum five groups of brilliant lines especially 
remarkable. The orange group, slightly less refracted than Na, is formed by four lines, 
the second of which is the brightest ; the third, not quite so bright, is closely followed 
by the fourth, which is very faint. The second (yellow) group contains seven lines, 
among which the fifth is brightest. The third (light-green) and the fourth (dark-green) 
group contain each nine lines. The third and sixth lines of the light-green group and 
the sixth and seventh (both near to each other) of the dark-green group are brightest. 
The fifth (light-blue) group (the distance of its middle part from H/3 and Hy is about 
in the ratio of 3 : 4) is formed by six lines, the second of which is the brightest, the first 
slightly less bright ; the last four lines, nearly equally distant from each other, are 
slightly less bright again. Two groups, of three fainter lines each, fall between the two 
green groups and between the dark-green and the blue. We may mention also two 
bright single lines, placed out of the groups — a green line preceded by an expanded 
one, and a light-violet line followed at a short distance by a bright band. Besides, 
there are in the spectrum more or less faint bands or expanded lines extending beyond 
Hy nearly as far as the distance between this line and H/3, i. e. about to Fraunhofer’s 
line H. 
22. We may denote the orange, yellow, light-green, dark-green, and blue groups by 
I, ii, hi, iv, and v, and the single lines of them by the arabic numbers, the place 
they occupy in each group being reckoned from the less to the more refracted. Thus 
by adding the chemical symbol of the gas we get a general method of denomination, 
mdccclxv. c 
