136 Messrs. Trowbridge and Richards on the 



not damped by the resistance of the tube, or other resistance 

 or impedance, produces the blue spectrum. 



It became now a matter of great interest to determine 

 whether the same conclusions apply to other gases, a subject 

 which has already been studied in detail by Wiillner and 

 others. The chief differences between our work and the earlier 

 investigations are : first, the use of a high-tension accumulator 

 instead of an electrical machine or RuhmkorfT coil as the 

 source of electricity ; and secondly, the introduction . of 

 varying ohmic resistance or impedance between the plates of 

 the condenser in order to study the damping of the spark. 

 It is the object of this paper to emphasize anew the importance 

 of the electrical conditions of the circuit, and to call attention 

 once more to the fact that the behaviour of most elementary 

 gases is in every respect similar to that of argon. 



With regard to the spectrum of nitrogen, it has been 

 known for a long time that two spectra could be obtained by 

 means of appropriate changes in the density of the gas, as 

 well as by the introduction of the condenser; but not all 

 investigators have put the same interpretation upon their 

 results. So varying are the views that Angstrom * and 

 Thalen f believed the familiar channelled spectrum to be due 

 to impurities in the gas. PJiicker and Hittorf f, Wiillner § 

 and Salet || have proved this view to be false, but they had 

 not at hand the constant current of high tension at our 

 disposal, and their nitrogen was obtained from air containing 

 argon, so that a revision of their work promised to be of great 

 interest. 



With our Plante battery of ten thousand volts we have 

 obtained the usual two different spectra of nitrogen by 

 varying suitably the electrical conditions of the discharge. 

 By means of a continuous discharge with no spark-gap or 

 brush-discharge in the circuit through nitrogen under varying 

 pressure we always obtained the channelled spectrum. The 

 glow in the capillary tube, as well as the positive and negative 

 light, was of a delicate pink colour under these conditions — 

 a colour not unlike the red glow of argon. When an air-gap, 

 over which the battery discharges in a brush, is introduced 

 into this circuit, the glow becomes more violet in tinge, and 



* Pogg. Annalen, cxliv. p. 300. 



t Bull. Soc. Chim, [2] xxv. p. 183. 



X Hoy. Soc. Proc. xiii. p. 153 ; Phil. Mag. [4] xxviii. p. 64. 



§ Pogg. Ann. cxxxv. p. 497, cxxxvii. p. 337, cxlyii. p. 321, cxlix. 

 p. 103, cfiv. p. 149. mm - _ . „ 



|| Ann. Chim. Phys. [4] xxvni. p. 52. Hasselberg, Ames, and others 

 have also studied the nitrogen spectra. 



