SPECTRA OF IGNITED GASES AND VAPOURS. 
23 
61. On sending the direct discharge of Ruhmkorff’s coil through a tube of glass from 
one-fourth to one-eighth of an inch in diameter, provided with electrodes of platinum 
or of aluminium, enclosing hydrogen at a tension of 5 to 10 millims., a luminous thread 
of light of a bluish-white colour was seen passing along the axis of the tube, without 
touching the glass. When analyzed by the prism, it gave a faint spectrum of the 
above-mentioned numerous bright lines, especially within the red and the yellow. 
Among these lines neither Ha nor Hy were seen ; H/3 only appeared, but less bright 
than many of the other lines. By interposing the Leyden jar and gradually increasing 
its charge (12), all lines became brighter, H/3 surpassing all other lines in brilliancy ; 
Ha appeared beautifully, Hy fainter. Hence we conclude that the numerous bright 
lines belong neither to the vaporized metal of the electrodes, nor to the decomposed 
interior surface of the glass, but solely to the hydrogen, constituting a new spectrum of 
it. This spectrum may be seen simultaneously with the three characteristic lines Ha, 
H/3, Hy ; but at an increased temperature, when these lines begin to expand, it entirely 
disappears. 
62. We got only one spectrum of oxygen in operating exactly in the same way as we 
did in the case of nitrogen, with merely this difference, that under the same con- 
ditions a spectrum of equal brightness was obtained only by means of a stronger 
discharge. Accordingly if oxygen, enclosed in the spectral tube, be replaced by com- 
mon air, the spectrum of the oxygen it contains does not appear until after interposing 
the Leyden jar. 
We do not enter here into the detail of the oxygen-spectrum, but conclude with a 
general remark. Nearly all luminous lines of the spectra of the second order expand 
when the temperature of the ignited gas increases beyond a certain limit ; but neither 
do all lines reach the same brightness before expanding, nor do the lines in the different 
parts of the spectrum expand at the same temperature. That is seen best in the spec- 
trum of the second order of oxygen. The bright lines constituting the characteristic 
groups of its middle part oppose the greatest resistance to expansion. If they are best 
defined, the luminous lines towards the red extremity, most distinct at a lower tem- 
perature, are already expanded, while towards the violet extremity the luminous lines 
are scarcely developed ; they will be brightly developed, become well defined, and 
extend very far, after the ignited oxygen reaches a temperature at which the groups of 
the middle part are expanded. Hence arises the difficulty of representing the oxygen- 
spectrum. A drawing exhibiting the well-defined lines successively developed in its 
different parts is rather an ideal image than a true representation of nature. 
63. Water introduced into a small spectral tube was kept boiling till the last traces of 
air were expelled, and then, before all the water was evaporated, the tube was hermetically 
sealed. The direct discharge, if passing, scarcely rendered the tube luminous, but with 
the intercalated jar the peculiar red light of hydrogen appeared, exhibiting the charac- 
istic lines Ha, H/3, Hy well defined. When these lines became gradually expanded, 
the lines of the oxygen-spectrum successively appeared with an increasing intensity, 
