﻿422 M. A. Wiillner on the Spectra of 



of it several lines stand out on each side of this place, which, 

 however, cannot be arranged in groups, and are not of great 

 brightness. 

 7th. In the violet part of the spectrum there are- — 



A bright violet line at 66 45 00 



A feebly bright group 6' broad, from 67° 3' to 67 9 00 

 A bright violet line at 67 36 30 



If the discharges of a small Ley den jar be passed through a 

 Geissler's tube filled with highly rarefied oxygen, just the same 

 spectrum is obtained; with a stronger charge it becomes more 

 brilliant without otherwise changing. 



When the spectrum obtained with a Holtz's machine is com- 

 pared with that described in § 9 as obtained with the RuhmkorfPs 

 coil, it is at once seen that both are identical, although, owing to 

 the greater brightness in individual groups with the Holtz's 

 machine, a few lines become visible which could not be seen in the 

 former case. 



It therefore follows that in this case, as also with hydrogen, 

 three distinct spectra may be obtained with induction-currents, 

 according as the gas in the tube has greater or less density. That 

 this difference in the spectra is solely due to the different tem- 

 peratures of the gas follows from the experiments with the Holtz's 

 machine. The same considerations which in § 7 led to the 

 continuous spectrum being regarded as that corresponding to 

 the lower temperature, and that consisting of groups of lines as 

 corresponding to the highest temperature, lead here to the same 

 conclusion. The continuous spectrum belongs to the lowest 

 temperature (although it is not seen with gas of great density), 

 because it is formed by the continuous discharge of the Holtz's 

 machine. The spectrum described by Plucker, which with gas of 

 suitable density may also be produced in its essential features 

 with the small KuhmkorfPs apparatus, belongs to a higher tem- 

 perature. The last mentioned, which is attained with gas of the 

 least density by the aid of the RuhmkorfFs coil and of a Leyden 

 jar, belongs therefore to the highest temperature. 



III. Nitrogen. 

 13. In investigating the spectra of nitrogen, Geissler's tubes 

 were filled with dry air, after what Plucker states had been con- 

 firmed, that dry air furnishes the same spectrum as pure nitro- 

 gen. With air in Geissler's tubes no traces of oxygen-lines are 

 seen ; and there is here no difficulty in getting the spectrum 

 free from hydrogen-lines ; the tube need only be filled a few 

 times with air which has been dried by sulphuric and phospho- 

 ric acids. 



