Multiple Spectra of Gases. 137 



the spectroscope shows that the red hands are relatively much 

 lower in intensity than before. By increasing the size of 

 this air-gap to its utmost limit, the red hands almost, if not 

 wholly, disappear, while the blue and green ones retain their 

 positions. Under these conditions the capillary tube is filled 

 with a pure blue glow, less intense and vivid than that of 

 argon, however. 



When the condenser is introduced, the whole appearance 

 of the tube is utterly transformed. The blue colour of the 

 tube at once changes to a rich bluish green, and the chan- 

 nelled spectrum gives place to bright lines, already well 

 known and mapped. This line spectrum corresponds to the 

 blue spectrum of argon. When the oscillations of the con- 

 denser-discharge are damped by means of a suitable resistance 

 or self-induction interposed between the condenser plates, a 

 channelled spectrum reappears ; but in this case the glow in 

 the tube is of a bluish-white colour, the positive and negative 

 lights being of a bright yellow. Whether or not this chan- 

 nelled spectrum is, as it seems, exactly like the one obtained 

 by means of a continuous discharge, photographic measure- 

 ment will show. This last appearance is probably the usual 

 one obtained by means of the Ruhmkorff coil, for then the 

 oscillations induced by the primary condenser are damped by 

 the impedance of the secondary coil and the resistance of the 

 tube. 



The spectrum of hydrogen is usually supposed to consist of 

 four bright lines :— H a (J563-0 (C), H /3 4861-5 (F), H y 

 4340-7 (G;, H 8 4101-9 (H), as well as several in the extreme 

 violet and ultra-violet *. 



Other spectra have been observed also ; but owing to the 

 partial understanding of the conditions required to produce 

 them, the voluminous literature f upon the subject leaves a 

 confused idea in the mind of the reader. The continuous 

 discharge of a high tension accumulator through hydrogen 

 gas at tensions varying from 0'05 mm. to 3 mm. and more 

 yields a beautiful white glow in the capillary of a Geissler 

 tube, while the strata in the positive and negative light are 

 often alternately pale pink and pale blue. When examined 

 by a spectroscope with a broad slit, the light from this dis- 

 charge appears to consist of bands similar to that of nitrogen, 

 as well as of bright lines ; but when the slit is narrowed every 

 band is resolved into a multitude of sharp lines of varying 



* 4mes, Phil. Mag. [5] xxx. p. 48 (1890). 



t Angstrom, Vogel, Lockyer, Fievez, Wiedemann, Higgins, Wiillner, 

 Ilasselberg, Balmer, Grunwald, Villari, Schuster, SaJet, Smyth, and 

 others. For references see 0. Damnjer, Anovgan. them. i. p. 369, 



