1864.] 



Ignited Gases and Vapours. 



155 



ment of which, however, while similar for the different hands, is quite 

 different from that observed in the channeled spaces belonging to the more 

 refrangible region. 



If, instead of sending the direct discharge of the induction coil through 

 the capillary tube containing nitrogen, a Leyden jar be interposed in the 

 secondary circuit in the usual way, the spectrum obtained is totally differ- 

 ent. Instead of shaded bands, we have now a spectrum consisting of bril- 

 liant lines having no apparent relation whatsoever to the bands before 

 observed. If the nitrogen employed contains a slight admixture of oxygen, 

 the bright lines due to oxygen are seen as well as those due to nitrogen, 

 whereas in the former spectrum a slight admixture of oxygen produced no 

 apparent effect. 



The different appearance of the bands in the more and in the less refracted 

 portion of the spectrum first mentioned suggested to the authors that it 

 was really composed of two spectra, which possibly might admit of being sepa- 

 rated. This the authors succeeded in effecting by using a somewhat wider 

 tube. Sent through this tube, the direct discharge gave a golden-coloured 

 light, which was resolved by the prism into the shaded bands belonging to 

 the less refrangible part of the spectrum, whereas with a small jar inter- 

 posed the light was blue, and was resolved by the prism into the channeled 

 spaces belonging to the more refrangible part. 



By increasing the density of the gas and at the same time the power of 

 the current, or else, in case the gas be less dense, by interposing in the 

 secondary circuit at the same time a Leyden jar and a stratum of air, the 

 authors obtained lines of dazzling brilliancy which were no longer well 

 defined, but had become of appreciable breadth, while at the same time 

 other lines, previously too faint to be seen, made their appearance. The 

 number of these lines, however, is not unlimited. By the expansion of 

 some of the lines, especially the brighter ones, the spectrum tended to 

 become continuous. 



Those spectra which are composed of rather broad bands, which show 

 different appearances according as they are differently shaded by fine dark 

 lines, the authors generally call spectra of the first order, while those 

 spectra which show brilliant coloured lines on a more or less dark ground 

 they call spectra of the second order. 



Incandescent nitrogen accordingly exhibits two spectra of the first, and 

 one of the second order. The temperature produced by the passage of an 

 electric current increases with the quantity of electricity which passes, and 

 for a given quantity with the suddenness of the passage. When the tem- 

 perature produced by the discharge is comparatively low, incandescent 

 nitrogen emits a golden-coloured light, which is resolved by the prism into 

 shaded bands occupying chiefly the less refrangible part of the spectrum.. 

 At a higher temperature the light is blue, and is resolved by the prism into 

 channeled bands filling the more refrangible part of the spectrum. At a 

 still higher temperature the spectrum consists mainly of bright lines, 



N 2 



