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XLIX. Atomic Hydrogen and the Balmer Series Spectrum. 

 By P. W. WoODj Professor of Experimental Physics, Johns 

 Hopkins University *. 



Part I. Atomic Hydrogen. 



IN the present paper an explanation will be given of 

 practically all of the very curious spectroscopic phe- 

 nomena observed with very long vacuum tubes containing 

 hydrogen, which I described in two previous communications 

 (Proc. Roy. Soc. vol. xcvii. ; Phil. Mag. vol. xlii. p. 729). 



The explanation has apparently been found of the 

 necessity for water vapour or oxygen for the development 

 of the Balmer spectrum — a matter which has always been 

 a mystery. Very remarkable effects have been obtained, 

 which show how important is the role played by the wall of 

 the tube and the gas film adsorbed on it. It has been found 

 possible to pump practically pure atomic hydrogen gas out of 

 the discharge tube and study its chemical and physical pro- 

 perties. Wires of certain metals and certain oxides, when 

 introduced into the stream of atomic hydrogen, come 

 spontaneously to incandescence and cause the formation 

 of molecular hydrogen. 



To make the present paper intelligible, it will be 

 necessary to recapitulate very briefly the subjects taken up 

 in the two earlier communications. 



It was found that if a hydrogen vacuum tube of moderate 

 bore (4 to 6 mm.), and a metre or two in length, was 

 excited by the discharge of a high-potential transformer 

 (or the direct current from a battery of dynamos), the 

 central portion of the tube showed only the lines of the 

 Balmer series, the secondary spectrum appearing only in 

 the vicinity of the electrode bulbs at the ends of the tube. 

 By using the central portion (suitably bent) " end-on/' 

 the series was photographed to the 20th line — a gain of 

 eight lines over previous laboratory records. 



The hydrogen was introduced moist from an electrolytic 

 generator through a long fine capillary, and continuously 

 withdrawn from the tube by a mercury pump. 



With small currents (0*5 to 1*5 amps.) in the primary of 

 the transformer, the luminosity of the tube was low, and 

 the secondary spectrum predominated, the Balmer lines 

 being very weak. As the current was increased, the 

 Balmer lines increased, and the secondary spectrum de- 

 creased in intensity, reaching its minimum value with a 



* Communicated by the Author. 



