[ 240 ] 



XXVII. The Spectrum of Hydrogeri Positive Rays. By 

 G. P. Thomson, M.A., Fellow and Lecturer Corpus 

 Christi College, Cambridge *. 



[Plate IV.] 

 1. Introductory. 

 A S is well known, hydrogen gives rise to two spectra. 

 XIl One, the Balmer series, is a group o£ lines of which 

 only a small number are easily obtainable under ordinary 

 conditions and whose frequencies follow a simple law ; the 

 other, the so-called second or many-lined spectrum, consists 

 of a large number of lines whose frequencies have not yet 

 been reduced to any law. 



The theoretical researches of Bohr make it seem very 

 probable that the Balmer series is produced by the neutrali- 

 zation of a positively charged hydrogen atom by an electron 

 moving through successive orbits. If this is true, it would 

 seem natural to ascribe the more complicated second 

 spectrum to the neutralization of the more complicated 

 molecule. Starkf has obtained results from the spectra of 

 different parts of the striae of the positive column in a 

 hydrogen-filled discharge tube, which lead him to the same 

 conclusion, but the evidence is not so direct as could be 

 desired. 



On the other hand, Fabry and Buisson J from measure- 

 ments of the width of spectral lines came to the conclusion 

 that the second spectrum was atomic in origin ; while 

 Wolfke § showed that a formula closely resembling that of 

 Bohr could be obtained for the Balmer series on the 

 assumption that it was due to the molecule. In addition, 

 there is the difficulty, which will be dealt with more fully 

 later, that, according to both Stark || and Wilsar IT, the 

 second spectrum of hydrogen shows no Doppler effect when 

 hydrogen positive rays are examined in the direction of 

 their motion ; while it is well known that when the positive 

 rays of hydrogen are analysed electro-magnetically by 

 Sir J. J. Thomson's method, a considerable proportion 

 generally consists of rapidly moving hydrogen molecules 

 with a positive charge. 



* Communicated by Sir J. J. Thomson, O.M., P.R.S. 



t Annalen der Physik, vol. lii. p. 221 (1917). 



X Journal de Physique, vol. ii. p. 442 (1912). 



§ Physikalisher Zeitschrift, vol. xvii. p. 71 (1916). 



II Annalen der Physik, vol. xxi. p. 425 (1906). 



«f[ Log. cit. vol. xxxvii. p. 1251 (1912). 



