66 Royal Society : — 



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

 through the capillary tuhe containing nitrogen, a Leyden jar he 

 interposed in the secondary circuit in the usual way, the spectrum 

 obtained is totally different. Instead of shaded bands, we have now 

 a spectrum consisting of brilliant 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 separated. This the authors succeeded in effect- 

 ing 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 interposed the light was 

 blue, and was resolved by the prism into the channeled spaces belong- 

 ing 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 inter- 

 posing 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, how- 

 ever, is not unlimited. By the expansion of some of the lines, espe- 

 cially 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 pas- 

 sage 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 temperature produced by the discharge is com- 

 paratively 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, which 

 at the highest attainable temperature begin to expand, so that the 

 spectrum tends to become continuous. 



The authors think it probable that the three different spectra 

 of the emitted light depend upon three allotropic states which 

 nitrogen assumes at different temperatures. 



By similar methods the authors obtained two different spectra 



