Electrodeless Ring Discharge in certain Gases. 12b 



increased and about 50 were measured, distributed amongst 

 the red and the blue spectra. At the lowest pressures, all the 

 lines belonged to the blue spectrum, but there was practically 

 nothing to be seen in the region between wave-lengths 5879 

 and 5144. An afterglow having the same orange colour, and 

 giving the same spectrum as the afterglow described in the 

 case of air, was observed in this purified argon at all pressures 

 except the higher and lower limits. 



In addition to the above gases were tried hydrochloric and 

 hydrobromic acids, sulphur dioxide, and carbon disulphide. 

 In the case of hydrochloric acid at medium pressures the ring 

 was bluish on the outer edge and reddish on the inner, the 

 difference in colour being due, apparently, to the presence of 

 the hydrogen secondary spectrum in the inner part of the 

 ring. At low pressures the red colour disappeared and the 

 blue extended nearly to the centre of the bulb. The spectrum 

 of the blue part of the ring was the four-line spectrum of 

 hydrogen and the chlorine line spectrum. Hydrobromic 

 acid behaved in a similar manner. The sulphur compounds 

 always gave the sulphur line spectrum and never the band 

 spectrum. In the case of carbon disulphide, the bulb was 

 coated inside with a deposit of sulphur after the discharge 

 had been running. The spectrum of the carbon was the 

 ordinary band spectrum, and not the Swan. 



Conclusion. 



These experiments clearly indicate a dependence of the 

 spectrum of a gas on the electric field responsible for ionizing 

 the gas. In most cases the results support those obtained 

 previously from observations of the discharge spectra of 

 gases in tubes with metal electrodes *. In such tubes the 

 intensity of the electric field has been shown to be greater 

 round the cathode than in the positive column, and should 

 also be greater in the intermittent spark discharge with 

 a leyden-jar in circuit than in the continuous discharge. 

 Now in the case of oxygen, the presence of four different 

 emission spectra under different conditions has been shown | ; 

 the elementary line spectrum in the leyden-jar discharge, 

 the band spectrum in the negative glow of the continuous 

 discharge, the positive line spectrum in the positive column 

 in a narrow tube, and the continuous spectrum in a wide 

 tube with a weak discharge. In the ring discharge the 

 elementary line spectrum is characteristic of the discharge at 



* Stead, Proc. Roy. Soc. lxxxv. (1911). 



t Schuster, Phil. Trans, clxx. p. 37 (1879), and others. 



