SPECTBA OF IGNITED GASES AND VAPOURS. 
27 
giving the distances of Ha and Na on one side and of Hy on the other side from H/3, 
by the following numbers of divisions of an arbitrary scale : 
139-6, 100-5-101, 88-5. 
In the first Plate portions of all the coloured spectra are represented as they appear 
by making use of two additional prisms of 45°. 
PLATE I. 
contains spectra of the first order. The first spectrum, N, belonging to nitrogen, is 
taken under such conditions that both its extremities appear equally developed. To 
the whole spectrum is added a representation of two bands, C, of its more refracted 
part, obtained by means of the four prisms. Here a determined number of subtle dark 
transverse lines produce the channeled appearance. Likewise the configuration of two 
orange bands, A, and two green ones, B, is represented, exhibiting the character of the 
less refracted part of the spectrum (15-19, 27, 28). 
S represents the spectrum of sulphur, as obtained by means of an exhausted bent 
spectral tube enclosing sulphur moderately heated by an alcohol lamp, and traversed by 
the charge without an interposed jar (35, 36). 
Two green and two blue shaded bands, as seen by means of the four prisms, are repre- 
sented by A and B. 
C I shows the spectrum of vapour of carbon obtained by the combustion of cyanogen 
in oxygen. It exhibits within the large shaded fields groups of peculiar bright lines, 
the brilliancy of which it was impossible to represent. These groups are denoted by 
a , b , c , d, e, f\ g , h. The red extremity becomes fainter when the heat of com- 
bustion increases, and even appears more distinct if the combustion takes place in air 
(41-46). 
The configuration of One of the red bands, as seen when the four prisms are employed, 
is represented by A. 
C ii exhibits the spectrum of vapour of carbon obtained by means of spectral tubes 
enclosing oxide of carbon, the gas being decomposed by the electric discharge (49, 50). 
On taking away all characteristic groups, the remaining part of the spectrum, consisting 
only of three large shaded fields, is that obtained if the density of the gas be greater 
and the discharge too strong (51), as well as in the case of imperceptible traces of 
decomposed carbonic combinations (8). 
C hi shows the less refracted part of the brightest of the large shaded fields (51). 
C iv exhibits a peculiar distribution of light and shade within the violet, scarcely indi- 
cated in Ci, but well developed when olefiant gas instead of cyanogen is burnt in 
oxygen (48). 
